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Lecture 28: Mitosis 2018 - Biology

Lecture 28:  Mitosis 2018 - Biology


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Lecture 28: Mitosis 2018

Biology Eleven


last period, we went over these notes on evolution ,
On monday, I would like for you to review the concepts in this set of notes:
How evolutionary change occurs
and these slides which show illustrations
natural selection

Furthermore, view this video on the steps of speciation and take notes on this. You will be given a work period mark out of 5 for making notes in your own words for "How evolutionary change occurs" and also for the Speciation video below.


Here's the crash course discribing Darwin's journey on the Beagle


Interesting. Mental thirst quenchinly good. Interconnected. Just enough info. Dr.kevin fun lectures.

ok. could use improvement please include that Kinesin and Dynein are ATPases that use energy. also that only Kinesin is displayed here. I was so busy looking for Dynein information, that Kinesin info went out the other ear. This could be better by improving the diagram.

This course is an excellent presentation of biochemistry. Professor Ahern presents the material in a clear, concise, easy to understand format that is easy to follow. I really like that I can pick and choose the lectures I need to watch, particularly those that I need to prepare for my upcoming exam. I find the review questions very helpful. Overall, I am finding the course very helpful and I am looking forward to completing more of it.

Like the step-by-step discussion. Make it easier for me.

See all 263 user reviews with text

Interesting. Mental thirst quenchinly good. Interconnected. Just enough info. Dr.kevin fun lectures.

ok. could use improvement please include that Kinesin and Dynein are ATPases that use energy. also that only Kinesin is displayed here. I was so busy looking for Dynein information, that Kinesin info went out the other ear. This could be better by improving the diagram.

This course is an excellent presentation of biochemistry. Professor Ahern presents the material in a clear, concise, easy to understand format that is easy to follow. I really like that I can pick and choose the lectures I need to watch, particularly those that I need to prepare for my upcoming exam. I find the review questions very helpful. Overall, I am finding the course very helpful and I am looking forward to completing more of it.

Like the step-by-step discussion. Make it easier for me.

not very engaging with the viewer, and it could be even more dynamic

I love it! It's clear and concise! Dr.Ahern is a gem to learn from. He breaks it down to where I can understand.

Nice speaker and illustrations. The lectures were engaging. Thank you!

Kevin Ahern is a really good teacher, I really enjoy his lectures, but sometimes it's hard to follow the lecture due to the presentation picturing one thing and him talking about something else. And also when he's talking about about the presentation I wished he had some sort of pointer so I would be easier to know what structure he's talking about.

I love her course. She explains in a very understandable way.

Beautiful and very good explanation . easy slides. thankyou. study matter also provided

The presentation is very nice and helpfuly The organization of topics was very good

I am no longer scared of metabolic pathways. thank you so much.

I'm impressed with how high yield the information is. The professor touches very important aspects in just the shortest time that one video has, and that is really impressive. I do have a degree in Biochemistry and molecular biology and so this is really making me master the course gradually. For sure I'm recommending this course to my friends from same college already who aspire studying medicine like me.

The videos are shorts and specific an also great explanations

I liked these explanations, but if you are a college student this may not be for you

Great explanation with great examples . Knowledgeable in subject matter , content up to date

THE TRANSLATION IS NOT CORRECT, THERE IS NO CONSISTENCY IN THE SENTENCES

Thankyou so much for the opportunity to relearn most of the important and key concepts related to this cornerstone foundation to Medicine & Life Sciences! Wish I had this tool in my undergrad days!!

He is the best here , I swear Idk but I like him

Great course for introductory level biochemistry. Prof. Kevin Ahen is a great teacher, knowing not only the topic but it's historical background.

He's a legend ooh I don't know what else should I say to complete 10 words

biochemistry was tough as I havent chemistry before. Had to keep reviewing, loved the tests and course presentation and so satisfying when i got the answers right. Great system for people like me . cant wait to do other subjects when i finish this one.

what an amazing lecture god bless u sir and i wish to meet u someday

Thank you so much Nonetheless, i really need to let you know your vocabulary is above my reach

I understand very well, thank you Professor Kevin, these help me a lot

It was much needed review for me in general. Thank you.

Enjoyed these videos very much. They helped me understand concepts I was struggling with.

Great work here. I’m so happy for the clearly understandable English

Nice course very complete in every sense, I like it, keep like that.

Awesome overview! Thank you! Particularly liked the gluten example. Also graphics were good - will stick in my brain longer.

I dont know if its the diagram or what the doctor is saying but i just cant understand the MAP kinase and the GEF and everything else afterwards

I just find the need for an extra time revising this, particularly offline. I always find my self making some notes unlike Anatomy!

Explica las cosas super simples y puntuales, se memoriza rapido de esa manera

I think it’s too fast, and not with details so please correct these problems

Magnificent lecture about polysaccharides and their functions for storage and release

The video highlights the important concepts about the hydrophobic amino acids group

I recommend include the cc out of slides screen, the letters do not allow to watch the information

adioasd oiaj doias ds dioas jdoias jdoas djoi asdjoia sd o

It's is just good that's why 4. I dislike that it's doesn't explain clinical too much

It's okay. But somehow hard to comprehend. I will love if you can make the teaching much easier to grasp.

Hi I appretiate her lectures about biochemistry, l hope the following lectures would offer me more interesting information.

this video is short and easy to understand. Thanks Teacher

Good explanation. Pretty bad diagram. Animation probably would work better.

Me encantan las clases son muy explicativas y muy detalladas , simplemente excelente.

i enjoyed every second of this video and it opened my mind to study more and become what i have always wanted to be a radiologist

Concise and clear exactly what I needed for this topic, thank you.

Good amount of detail in digestable amounts. Very much appreciate able to run the videos at different speeds.

No explanation at all just reading , sorry for that , No interaction

It's great to learn from someone who's enthuisiastic about their specialty and even better at teaching it. Thank you Dr. Ahern (:

I like the short videos. They described what’s important and later you get questions about the video.

Me agrada como explica las cosas la Dra, creo que lo hace que sea entendible de forma sencilla para cualquiera

I love having access to such rich learning material, thanks for making this an available resource. My only criticism would be that the quiz questions could use improvement and the professor could talk slower to make note taking easier. Overall, very grateful to have found this!

It is a good explanation for a complex topic, with only the most important

complicated topic but I think I got it, though the Tyrosine kinase itself is a bit complex

I like the format - the lectures are "short and sweet". The lecturer is reasonable easy to listen to. Perhaps it is just because this is a foundation course, but it does feel this material may not be in-depth enough for USMLE step 1. (Or perhaps because it's re-used for non-USMLE students?). The questions are just "okay". There are a few errors, and a couple questions could be worded better. It also seems that some of these questions are testing material that seems only marginally important, and may not be very "high-yield". I wish there was an option to flag review questions to not be included in the "spaced repetition". The "spaced repetition" idea should be for memorizing the most important details, and I don't really want to be memorizing questions that I think are of little importance, incorrect, or poorly worded. (It'd also be a good way your you at Lecturio to decide which questions should be revised - if many people flag it as "don't review again", the question probably needs revision.)

Understandable. Easy to remember! And pretty useful. You really need to learn basics topics in Med career it surely make you to be highlighted over another students

It helped me clarify some topics I had been having trouble with.

Sorry, the following videos have the information that I was looking for, sorry again

the instructor is very clear and is easy to follow

Dr. Cornwall did a very great job with this.. The big picture simplified everything and made studying into little details easy.

el contenido esta muy bueno, solo que la traducción tiene falencias y dificulta entender los conceptos adecuadamente.

Everything is confusing. The diagrams and what she was saying didnt allign. ALso she never gave the answer to the number of chromosomes in each stage of meiosis and mitosis

I loved it, really interesting and easy to comprehend, thank you very much :)

Need more mcq 's for practice and good content. Very clear concept s

The lectures are great. But I just feel like they are too expansive. Not very suitable for a dedicated study period

Very good Thanks Really it doesn't take much time and its really good

the lecrure is detailed and very comprehensive it is well presented i also liked the quiz that comes afer the lecure.

It almost always fails to explain 'why'. These lists are available in any textbook. I was looking for an explanation to understand it. Also, visually it is looking at a table for 5 minutes, pictures could have explained better.

Dear sir/madam In regard to the Biochemistry basics,I am much satisfied by the cours.In fact,the videos concerning biochemitry basics are well summarized and are full of useful information in the regard of médical studies.Because of this,I am enjoying the course and continuing either to learn much more . Yours sincerely Asher Hategekamungu

Dr. Ahern is a fantastic lecturer. All the course is simply awsome.

The video episodes are way too short, need to go back and start over every 3-4 minutes. I think there should be a option to view the topic in one full video. Otherwise the subjects are well covered in an understandable manner. Many thanks

The way of teaching of Georgina is really impresive, i understanded everything. The best classes ever.

The course was easy to follow and has good illustrations of the concepts. I also like the quiz portion of the course.

Very comprehensive lecture . It' s clear and simple. Thank you for your work .

Great professor and easy biochemistry topics to learn with good explanation.

I work in a large public hospital biochemistry routine department, when I studied this subject there where no computers, only text books. So this is a refresher and update of the subject. I am enjoying this 'new' way of learning and it enhances my work knowledge as understanding theory is important for performing work well.

Great lecture! Very simplified and friendly explained. Thanks so much !

I like his style and respect his effort. I've been using these lecturers to review my knowledge

Dr. Cornwall makes the topics easy to understand and retain. Her approach is not overwhelming but yet not so simple you are bored.

Very detailed. Moves through information and a good pace. Sifts out the important information versus stuff we don't need to know for the exam.

the concepts are clear and the time is enough, examples are short.

hi Biochemistry's videos are interesting and give me information, the orator pronounce correctly. As you know I do my best to prepare ecfmg exam and board examination next, of course after having sufficiently training and advices under your guidance I would like to apply ecfmg examination this year, now would you please give me more information for preparing step one and step 2 exam.

I believe the term is entropy is misused in this lecture.

Misuse of the words fludity and stability as if they were synonyms makes answering the question at the end confusing. Other than that, it's a good lecture.

Awesome analogy great lecture! Very nice lectures overall I really enjoyed them. even though I have taught this topics and I know them fairly well. I enjoy little gems of information I received through these lectures, and new understanding

I like how Dr. Cornwall recaps chemistry and relation to energy to cells. Her hand motions help with my learning and understanding. Thank you.

two stars just for the effort. But its ore like reading fro book. Nothing different. Very boring. No interaction.

I like the practical comparisons used for better understanding and remembering the topic, makes it much easier and more entertaining!

Concise and to the point for basic understandment of the subject.

Talks clearly and explains all the key points so that you can understand the lecture in simple terms

Studying Biochemistry lectures helps me to understand and hold in memory every each case. so this is the best ever

It was a great lesson thanks for everyting short and briefly everyting.

It’s not a bad lecture but it’s bulky stuff that isn’t simplified to hold ones attention, don’t get me wrong, it has its highlights but it could be more interesting.

Great lectures, very clear and understandable! Thank you, Dr Georgiana Cornwall!

Great lecture which allowed me to understand the topic much better than I was taught

All the explanation are precise to the point. and covers all the important concepts

Explains concept very well with good analogies that further enhances my understanding.

Dr Cornwall has the gift for teaching!! She explains things very well, thank you!

The professor is excellent. I like how he explains things. Some of the professors move their arms around a lot which can be distracting or spend the whole time looking down at the computer. With others it feels like all the do is read from the slides. However the biochem lectures are very well done and by far my favourites so far.

The module is complete but the questions can get too easy

I really enjoyed the video and it made me learn, also I liked that are short videos

They are so awesomely explained and very helpful thank you. I’d love the videos to have that ten second rewind or fast forward arrows like YouTube does, and then it would be perfect.

Very concise. Great illustrations. Thank you. Thank you. Thank you

Thank you for your knowledge and for spreading it in this way for us, the students.

The lecturer makes the topic interesting, easy to understand. One begins to appreciate how these things link with everyday human existence and how they play a pivotal role.

Good, where are the rest of the organelles (like peroxisome)

Need lot of detailed explanations.. especially in videos. The teacher is really good but the script is lacking too much.

its good and thorough, also covers minor lipid types! good to learn

Explains it completely from the start to the end , everything is clear and simple . The structure is very easy to understand.

I love this app but can get a little confusing when the professor uses the wrong words or accidentally says the wrong thing. Do you not edit errors out? It’s a great platform just needs a few tweaks here and there.

I am a student at Downey High and I really want to be a cardiothoracic surgeon, and I didn't know what to learn but I know this website will help me.

This is pretty good introduction! haha how to control the cell cycle

just basic to litle details course.easy to understand it.

I think it is an entertaining way to learn the history of Biochemistry.

I love this guy. The way he explains makes Biochem look easier

He is clear, short, and simplify the most important points

he is very clear and is a nice teacher, and he use a appropiated nivel of technicims

I like so much the content of this course and how the doctor provide the information

I really liked this site ,and it's seems helpful for me . I am a high school student. I am in the 10th grade right now. I just want to become a surgeon doctor because I want to save peoples lives. I know that I have to right a commit to this site and I do not have to introduce myself for you people. I do not need to study this because I did not understand today's subject.I just want to be ready for the medical school. I hope this website will help me being ready and ,Good Luck.

Concise with good use of slides and professional presence and dress.

P53 GeneRate this lecture P53 Gene Rate this lecture P53 Gene P53 Gene P53 GeneRate this lecture

extremely helpful when the amino acids are divided in functional relevance.

Amazing lectures. Simplifies complex pathways and process. Really fantastic! Watched every lessons.

:) Thank you . everything in this lecture is clear. like it very much.

Almost no information really disappointing. Use Step 1 2018 page 46 . Even a student could have presented the topic in more depth as it is important.

just excellent , the content and the preparations were realyy excellent and goes very easy.

I believe that she is a great lecturer but, the issue is the way of delivering the lesson and how much was she ready to record the tuition. anyway it was a good experience for both of us, she let me search a lot for the genetics to unwind condense informations :)

This is only the first lecture and the first time I am delving into biochemistry for the first time, so hard to say, but something about Prof. Ahern's manner makes me curious and creates a fine feeling of anticipation. Great for a first lecture.

Very disorganised way of explaining concepts It would be much better if things were presented in more detail and if the presentations were structured adequately

it was described in a simple and easy way to understand, thank you.

This video did not really show Aspartic Acid or Glutamic Acid?

The lecturer did not appear confident looking into notes too often. Too many hand gestures are a distraction especially when not pointing to the stuff on the slides. The material was not presented in an easy or simple way. Made it more complicated that it actually is. I feel difficulty in continuing to the next lectures without understanding this.

He very easily simplifies things. So this is why I give him a five star review

Amazing, loved it very much. Easy to follow and clear.

Awesome lecture, awesome proffesor. My teacher spent almost 1 hour explaining that. Thank you Dr. Ahern

I feel like she is just reading notes that she has been just handed over.

The presentation is simple, short and concise preparing students for more detailed content. I believe that this is an efficient approach toward a broader base of an audience. Thank you!

as a beginer i didnt couldn't understand anything the lecturer is talking about and the lecturer is way too fast

My name is Barbara, I'm from Colombia and I really like your videos Mr. Kevin, because I think the content is easy to understand.

Dr. Cornwall is very thorough and paces herself very well in relating core concepts.

Very well explained and detailed lecture, but it would be nice for better understanding to have some names and terms (e.g. Ramachandran plot) displayed in the video!

way too fast . I really wish the teacher would talk slower as now I keep having to pause and rewind etc.

So much more simple than my lectures. Thanks for the detailed lecture. You're a life saver.

Direct , and easy to follow. The length of the video also helps.

Great professor but unfortunately the details of this lecture are not important for USMLE Step 1

Easy to understand and the explanation are very clear. Thank you very much good job!

In my school we will take this lecture in 2 hours. Way too short and superficial

Needs more details, and take it slower so that we the audience can get a more thorough understanding of the topic (the video really doesnt need to be that short)

I found it really helpful. Your explanations were clear and easy to understand.

As much as your stories are interesting for the ETC gradient It does not fit my learning style. It would be nice to have clear scientific language about what's happening. I can't write a story on my exam paper. Perhaps this is just me.

Easy to understand and very complete. Thank you for your time, helped me a lot

Thank you for the video's theses are really helpful. look forward to keep learning.

Feels like she is not comfortable with information she is teaching. Accuracy of information (and spelling!) is sometimes questionable.

very nice clear and organized lecture. thank you. it adds alot to my simple knowledge

Great Explanation !! I wish we would have had you as a teacher. :)

thanks for teaching me in such a clear, precise, and yet enriching way

excellent lecture. Cristal clear not too slow not too fast, smooth transitions and a bright ending

It was very precise and up to the point. The presentation was interesting that triggers to study better .

very good lecture. pretty well organized and instructive. He has a deep knowledge of the material making me to pay special attention to all his lectures.

Very nice and informative lecture, easy to understand and remember

I have followed Dr Ahern through all the basics of biochem lectures and he has never failed to deliver.

Great job, Dr. Ahern. Thank you for bettering my understanding of these concepts! Used as a supplement to lectures and powerpoints, your videos on Lecturio have been extremely helpful to me!

Very good lecture, l consider that is one of the most complete themes that l´ve read . good job.

I am a biochemistry student studying in the UK I found this so useful especially as a foundation in my initial year of study.

I love the visuals, her method of speaking and the transcript at the end

You make it much more easier. However, I still understand all important points. Thank you!

Good lecture, but not USMLE focused. This is more of a general biology lecture than a USMLE prep lecture. It seems to me that Lecturio is not making the difference between MCAT prep and USMLE prep. The lectures look more like MCAT prep lectures and not USMLE.

I like the way she expresses, you can easily understand her

best prof in the world explains everything so good that even a kid will understand

Its a little bit dificult to understand but the information its complete and tables and graphics helps a lot

Really great explanations of the whole process. Was not happy that I had to relearn Krebs and ETC but actually found these videos enjoyable and valuable.

Great enzyme analogy! Enzyme is the friend who puts his two other friends in contact with each other so that they can start talking and dating )

Nothing on how p53 relates to RB or how p53 induces p21 to inhibit CDK thus acting as a tumor suppressor by not allowing cell cycle progression. This info is found in the the First Aid for the USMLE so it is probably important.

In terms of studying for something like USMLE, brief intro is fine! Such topics will not be tested on the exam but are necessary to build foundations for other future topics. If you are studying for other exams, this whole module may be a bit light on key information. Great as a refresher though!

Conveyed the process in a short &digestable way.I LIKED THE WAY OF presentation too.

his teaching is clear and it is not allowing me to get even a single doubt

i could understand the concepts better. explanation was good.the charts were self explanatory. it made me feel bio chem much more interesting.

I like the way you link things from one to another. Yuu made these lectures highly appreciated with the concise and comprehensive explanation! Thanks Prof!

This is not a USMLE 1 focused topic, an important material for the step, it's so superficial either the question that is a first order question. Need to going deep in the topics, we're not an undergraduate students.

i like your teaching .sir. it helps me to understand the concepts clearly.

Excellent information and explanation, it's helping me a lot. Congrats, lecturio!

First of all I would like to say that I really appreciate all of the effort by the professors and Lecturio to do great lectures, however, I would like to say, as well, that you need to focus on the exam format (In this case - USMLE Step 1). For example, in this lecture it was asked: "Which of the following is NOT a lysosome related disorder?" that is pretty good, because it has a clinical context with the subject, however this " lysosome related disorder" have never been taught by Professor Cornwall.

Very clear what is going on. I understand it much better.

Loved the lectures, especially the lecture on the electron transport chain. Dr. Cornwall had a really useful analogy of the ETC and kids (electrons and hydrogens) going to the prom (ETC) that really made the concept stick. Very good job!

The chapter about cellular structure has given me clear explanation and enhance my knowledge about the different functions that the plasma membrane assure. The course just makes my understanding of cell dynamic very straightforward.

It's an excellente teacher! She uses easy analogies that you can memorize quickly and gives you a summary of your class (in my case). Greetings from México!

High yield facts and clear explanation, the fundamental elements and efficient route to master biochem!

I am new to this curriculum, however, I would like the lectures to be longer. I am hopeful that other lectures are much more detailed, e.g. gene regulation/expression. Lecturer is very knowledgeable, clearly.

I liked very much this course. It's very interesting and The good teachers.

very good, is complicated, but i understand everything, she is a good teacher

I agree that it was brief if someone was looking for something more comprehensive. It was sufficient for me as I only required this to understand one lecture slide however not enough questions.

Gooood job LoL and really a good story-maker. Thank you very much! Amazing, very impressive!

Thank you very much!! So funny and interesting! I laughed many times LoL also learned A Loooot.

I do not think there can be any simpler explanation of these concepts. Dr. Cornwall takes her time to explain these concepts in a way that they stick with you, and the analogies she uses engrave them into the medulla so that you can relate to the concept. You can't beat this! This is exceptional. Thank you so much!!

First step to refresh and understand different concepts. Highly recommended.

I like the fact that the lectures are detailed and Dr.Cornwall makes it fun and easy to understand.

This lecture was excellent in every way, I must say DR. Cornwall is a Pro in intermediate metabolism. I couldn't understand this processes better in medical school than she has made me.

Based on explaination. I felt there was some lack of informations. In some area needs to be more profound.

Great lecturer who is knowledgeable about the subject. However the animations in both mitosis and meiosis would have been in motion so the explanations were tuff to follow. overall good attempt. keep up the good job.

great lecturer who is very knowledgeable about the subject matter, pitch, diction and pace is terrific. keep up the good job.

Excellent lectures, you can understand in a few minutes the basics of difficults topics

couldnt understand a thing. Please try to use animation to explain better

Classes have an excellent quality, however there are small mistakes when you´re reffering to some specific molecules such as cAMP and cGMP because in some ocasions, you tend to exchange one with the other in just a few ocassions. Nonetheless, the overall course is excellent, with clear explanations.

How I wish I had this when I first started medical school. The explanations were clear and concise. The use of simple words enable me to understand it well as well as the option to pause at anytime allows further internalization of the facts.

u r so good like honestly amazing thank you so much professor

I learned a lot about cell structure in the most simple and efficient way.

It is too much Helping. It is Awesome and helpful

The lecturer uses great analogies to make concepts easier to understand.

Very good explanation of concepts. Animation could be added for excellent explanation.

Every topic was clearly explained and I could understand them very well.

The lecture was very intriguing! Dr. Ahern is so well articulated!

I don't waste my time going to any biochemistry lectures at my medical school because I know that Dr Cornwall explains all of the content more clearly, in more depth, in less time. I always finish her lectures excited for the next one!

Brilliant! I have always found these topics extremely confusing at medical school, but Dr Cornwall is able to explain them in such a way that they seem straight forward and easy. This certainly replaces lectures for me! If anybody is unsure about trying this course, they should definitely try it! Dr Cornwall is the best biochemistry lecturer I have seen!

A great lecture. I am a high school student and i struggle with biology. I get a better explanation from your lectures and I am not even a native English speaker. Thank you so much!

the lecture is good it educates on how bichemistry is related to other fields in life

I think this course is really informative, though I would like some more details in subjects like RTKs and G coupled proteins. And also please add English subtitles to this course! I'm not native and I found it hard to keep up!

The courses are very concisely presented, it is really useful for preping for an exam

Need more details Need to go slower But overall not bad

The lecturer is very good at getting biochemistry across. Well explained and understandable up and until here.

Needs more substance. This was barely long enough to be an introduction.

Professor Dr. Kevin Ahern is very clear in presenting. Love the short but very informative lectures. Would recommend to everyone, those with or without biochemistry understanding. Thank you very much Professor and Thanks to the maker of Lecturio.

Good clear concept review. Could use more specifics regarding cyclin and cdks.

Everything was on point .. Will definitely share with my friends.

Very concisely put, I love the lectures, very helpful indeed. Now all I need to do is work my ass off to get the dollars to pay for this awesome lecture. Thank you Lecturio!

I found the lectures to be very informative and composed of high-yield information for a relatively quick review of the subject. The only reason I give 4* is because of the few technical problems with the course but, in regard to the course material, Lecturio provides a wonderful review of Biochemistry with Dr. Ahern.

I like the way that the AA are presented by a table between essentiel and non essential. I will use it for my memorizing process.

Great/clear explanation, definitely recommend to students. For those that complained, please describe what's needed to be explained, or just keep your pie hole closed. Being ambiguous is pointless.

I like the teaching style and material presented! It is clear and understandable. Thank you!

It's very clearly explained and very useful for my studies. I would like it to be a bit more detailed but not too difficult.

Kevin Ahren explained the part very well. I liked the way he explaining this part. I am from business back ground.

i like this lecture. way of representing and explaining is quiet good.

Very nice but there's some need of detailed explanation and then it would be perfect

Awesome job, I wish you were my teacher at my university! So clear!

What I loved the most about this lecture was how Dr. Cornwall actually took her time to explain the concepts discussed, and even used simple analogies to ensure that the information was easier to digest. This is something you find lacking in many professional lectures. Thanks again Dr. Cornwall!

very good course, i wish i have money to pay the all course

Thank you dr. Georgina Cornwall! Everything was perfectly understood with your lecture!

She spends half an hour explaining the steps of meiosis and doesn't even get into details. I'm not sure how she can manage to explain such simple topics in such a long time (it's half a movie time, for God's sake!). She should base her lectures on Molecular Biology of the Cell, by Bruce Alberts et al., AT A MINIMUM. Lecturio has many excelling lecturers unfortunately, Dr. Cornwall is not one of them.

These lectures are made simple for someone like me who is very vulnerable to biochemistry.

As it's my first lecture, I think I have to work a lot for getting great benefits from your great tutors. hence I had to give this rate. right now there are no such dislikes. well, thanks a lot for the kind assistance.

Great lecturers and thorough explanations for every subject. After watching the lectures, I actually understood and retained because his lectures are extremely well organized.

This is quite helpful. I am a pre-Medical student and I'm fully satisfied by the leacture. I'm able to cover all the syllabus. It's helping me to save time. I dont need all those notes n stuffs. Most important i can practise lots of questions! I'll recommend all Medical students to take this amazing leacture for once so that you'll be able to understand. Thankyou @lecturio! .

A ERY INTERESTING COURSE ,BUT REQIURES A LLOT OF STUDY TIME TO UNDERSTAND THE AMINO ACID CHEMISTRY. TO BE HONEST, I AM A RETIRED 85 YR OLD PHARMACIST TREYING TOEEP UP.

I really like the pace and clarity of this lecturer in how he presents the material. It would be nice to have animated pictures in signaling and transport. I also wish there were sections covering enzymatic catalysis & kinetics. Over all, very good! Thank you for making these

She is very detailed but yet not overwhelming with the lecture. It's been great help on my bio knowledge.

Not very hard to understand, sometimes a bit too "shallow". However most often very good. Even great.

I rate this five stars because I like to go over it while I do other things and more than once.

The overview of biochemistry is really helpful! The images are great, and the lecture is really high quality.

I was hoping for a little more details about the chemical makeup of the topic, however, I like how the entire video is layed out and described.

The Dr Georgina did it very well she know detail about the subject matter andinet did not express about her and execelentroll model for me!

I like the way the instructor presents the material , and the examples she uses.

Well, I love the way Dr. G explains, however, the lecture on cell control wasn't the best and needed more explanations and needed to be more simplified . I put five stars because Dr. G has helped me a lot and made Biology a fun course.

This course really helped me understand the cellular structure, I learnt more from one of the 20 minute lectures, than I did in a 3 hour lecture at university, so these really help!

Good and clear explanation, Dr. G makes it fun to learn biology.

Watching these videos from Lecturio is very much like being in my school. The difference is Lecturio is more fun and it encourages us every time we want.

With this introductory course, you will be exposed to the basic aspects of Biochemistry. Professor Ahern emphasizes that an in-depth knowledge of basic biochemistry will aid you tremendously in understanding life processes on a macroscopic level. This one course alone was well worth the one month payment of 24$. Every other course on top of that was an attractive but inessential addition. "icing on the cake"!

Professor Ahern is truly excellent! Amazing choice. He clearly explains concepts and shows sincere enthusiasm for the topics. You need to bring him back for lectures on amino acids and the urea cycle as well as the electron transport chain.

Very easy to follow, good flow and simply explained, exceptional professor! just wish the questions had explanations then I would give the videos a higher score .

it has helped me build my understanding of biochemistry. looking forward to more lectures

Love this course and Professor Ahern's enthusiasm keeps my attention. Being able to watch the videos over and over helps the lessons sink in. For the first time I'm enjoying biochemistry. Thank you for making these videos so affordable and easy to use.

Since is starting this biochemistry, it's help me to remember some of the basic concepts that I have forgotten

This is an amazing course! Prof Kevin has made every single details simple and clear. His deep knowledge and understanding of this subject is well reflected in his teaching style. The materials he used, are very attractive which makes it easy to memorize. I would definetly recommend this for both under and postgradustes students.

This course is well done. It's thorough. I'm reviewing things I've learned, and also moving on to more advanced material very soon. I wish I would have had this during undergrad.

The biochemiThe biochemistry is one of the best because the professor Ahern is a terrific docent who makes one love the lectures


DNA Replication Determines Timing of Mitosis by Restricting CDK1 and PLK1 Activation

To maintain genome stability, cells need to replicate their DNA before dividing. Upon completion of bulk DNA synthesis, the mitotic kinases CDK1 and PLK1 become active and drive entry into mitosis. Here, we have tested the hypothesis that DNA replication determines the timing of mitotic kinase activation. Using an optimized double-degron system, together with kinase inhibitors to enforce tight inhibition of key proteins, we find that human cells unable to initiate DNA replication prematurely enter mitosis. Preventing DNA replication licensing and/or firing causes prompt activation of CDK1 and PLK1 in S phase. In the presence of DNA replication, inhibition of CHK1 and p38 leads to premature activation of mitotic kinases, which induces severe replication stress. Our results demonstrate that, rather than merely a cell cycle output, DNA replication is an integral signaling component that restricts activation of mitotic kinases. DNA replication thus functions as a brake that determines cell cycle duration.

Keywords: CDK1 DNA replication G2 phase PLK1 S phase cell cycle mitosis replication checkpoint.

Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

Figures

Plk1 Activation Correlates to Completion…

Plk1 Activation Correlates to Completion of DNA Replication (A) Schematic of hypothesis. (B)…

Suppression of DNA Replication Initiation…

Suppression of DNA Replication Initiation by Targeting CDC6 and CDC7 (A) Schematic of…

DNA Replication Controls Cell Cycle…

DNA Replication Controls Cell Cycle Duration (A) Asynchronous RPE CDC6 d cells were…

DNA Replication Restricts Activation of…

DNA Replication Restricts Activation of PLK1 (A) Examples of U2OS cells expressing PLK1-FRET…

DNA Replication Restricts PLK1 and…

DNA Replication Restricts PLK1 and CDK1/2 Activity to Prevent Replication Stress (A) Asynchronous…

DNA Replication Limits CDK1/2 Activation…

DNA Replication Limits CDK1/2 Activation upon S Phase Entry (A) Single U2OS cells…

Model for Integral Role of…

Model for Integral Role of DNA Replication in Human Cell Cycle Wiring Proposed…


Chromokinesins

During the cell cycle it is critical that the duplicated DNA faithfully segregates to give rise to two genetically identical daughter cells. An even distribution of the genome during mitosis is mediated by mitotic spindle microtubules, assisted by, among others, motor proteins of the kinesin superfamily. Chromokinesins are members of the kinesin superfamily that harbour a specific DNA-binding domain. The best characterized chromokinesins belong to the kinesin-4/Kif4 and kinesin-10/Kif22 families, respectively. Functional analysis of chromokinesins in several model systems revealed their involvement in chromosome arm orientation and oscillations. This is consistent with their originally proposed role in the generation of polar ejection forces that assist chromosome congression to the spindle equator. Kinesin-12/Kif15 members comprise a third family of chromokinesins, but their role remains less understood. Noteworthy, all chromokinesins exhibit chromosome-independent localization on spindle microtubules, and recent works have significantly extended the portfolio of mitotic processes in which chromokinesins play a role, from error correction and DNA compaction, to the regulation of spindle microtubule dynamics.


CXC CSEC Human and Social Biology - Lecture notes

Here are lecture notes for the CXC CSEC Human and Social Biology exam that have been posted on the internet by Portmore Community College, Jamaica.

They have also posted specimen papers for the CXC CSEC exam in Human and Social Biology as well as the GCE Human and Social Biology exam.

This information will be useful for those students preparing to sit the CXC CSEC Human and Social Biology exam.

Michael Dane Lewis (not verified) 11 September 2010 - 9:08am

Math, English A, Social Studies & Office Administration

I love what I see so far, it has helped me alot.

mello (not verified) 17 September 2010 - 5:51pm

Thank you for this site. Im about to start HSB studies for exams in January, anyone willing to guide me more please , I hope I can cover all topics that are necessary!

guest (not verified) 13 August 2011 - 10:00pm

In reply to new by mello (not verified)

Human and social biology

I'm about to start HSB studies for exams 2012 in January anyone willing to guide me more please, I hope I can cover all topics that are necessary!

Elesia (not verified) 18 September 2010 - 1:22pm

Human & Social Biology

I would be doing the HSB exam in January, and I'm just checking for the syllabus so that I would have a clear and precise idea of what to study for

guest (not verified) 14 August 2011 - 9:53am

Whats happening i cant see my

whats happening i cant see my results, why did they even bother to have an online site.thats T and T for ya CRAP all the way.t

mmmm (not verified) 23 May 2012 - 7:17pm

In reply to whats happening i cant see my by guest (not verified)

About cxc

can you utilize H&s/CHEMISTRY alone to enter PREMEDICINE at the college level,without PHYSICS.And if not,what if you obtain CAPE BIO and CHEM.I want to attempt.thk u.

kerry thomad (not verified) 23 August 2012 - 10:11pm

Human and social biology

hmmm going to try and do this subject for the first time

Mad Head (not verified) 9 November 2012 - 4:55pm

Signning up

How do i sign up for this website.

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We are not registering new members at this time.

Human and social biology

i believe this will help me in getting notes on human and social biology.


Biology Eleven


I gave you a colouring book showing the structures of flowers, leaves and fruit.
Use this as a reference.


FLOWER LAB IS OUT OF 20 MARKS
Go into the school garden and find the following specimens. Bring them back for dissection and observation under the dissecting microscope.
Draw each specimen. 2 marks
Identify the flower type and label the parts. 2 marks
Write one interesting observation you notice 1 mark

Each drawing should be at least a half page. You should have three specimens:

Use a big legal size paper to draw your observations.

1. Find a small HEAD type of flower (simlar to a sunflower) It ought to have a disk flower and ray flower within the head. Observations: Count the disc flowers in your specimen. What is the advantage of this kind of flower?

2. a. Find a SPIKE type of flower
b. Find an UMBEL TYPE of flower

3. Find a BASIC FLOWER. Is it hypogynous, perigynous or epigynous? Draw it and label its parts

CONTENT: YOU COMPLETED THE ASSIGNMENT 15 MARKS (5 marks per question)
you answered all the questions with care and you discover something interesting/

CARE IS TAKEN IN DRAWING and observing out of 5
6/5 you make exceptional, careful drawings with clean lines. It is beautifully done and neat, it's in colour. This stands out. Bonus marks
4-5/5 you make exceptional careful drawings. This is beautifully done and neat
2-3/5 your drawings are complete and neat
1/5 you needed more time as your drawings seem a bit rushed and incomplete.


SEED AND FRUIT LAB ALSO OUT OF 20 MARKS

For each specimen, draw it and label its parts. Write a few sentences that describe its role in angiosperm reproduction. Each drawing should be at least half a page and neatly drawn, in colour.

draw three seed specimens 5 marks: Which of these are dicots and which are monocots? How do you know?
soybean sprout
corn nut
coconut


Fruit specimens: 5 marks Classify these according to your colouring book
strawberry
dragonfruit

find one more fruit OR seed specimen in the school garden 5 marks

RUBRIK
CARE IS TAKEN IN DRAWING and observing out of 5

6/5 you make exceptional, careful drawings with clean lines. It is beautifully done and neat, it's in colour. This stands out. Bonus marks
4-5/5 you make exceptional careful drawings. This is beautifully done and neat
2-3/5 your drawings are complete and neat
1/5 you needed more time as your drawings seem a bit rushed and incomplete.

CONTENT: YOU COMPLETED THE ASSIGNMENT 15 MARKS (5 marks per question)
you answered all the questions with care and you discover something interesting/


Advanced Lecture Course on Systems Biology

Systems Biology is one of the most prominent newly emerging interdisciplinary science areas. By connecting fields such as genomics, proteomics, cell biology, medicine, molecular biology, biochemistry and genetics, with mathematics, bioinformatics, engineering and computation, it enables discovery of yet unknown principles underlying the functioning of living cells. At the same time testable and predictive models of complex cellular pathways and eventually of whole cells are generated, which are useful for efficient experimental design and bioengineering and the network-based design of drugs and therapies. This advanced lecture course will cover essential and state-of-the-art aspects of SysBio from principles and methods through the modeling of living systems to applications in biotechnology and medicine.

We were able to commit many leading experts to participate as lecturers, tutors, black-board teachers and informal poster discussants and we are thus confident that this course will be an outstanding lecture course with an exquisite scientific program. It will open the doors for regular student training in Systems Biology in Europe, provide a basis for a human network of young Systems Biology experts, and provide a centre for other Systems Biology discussions between scientists and funders.


PROLIFERATION RATES IN NORMAL TISSUES AND TUMORS

When cultured cancer cells are treated with paclitaxel or a kinesin-5 inhibitor, only cells that enter mitosis are killed or rendered senescent (Baguley et al., 1995 Blagosklonny et al., 2006 Gascoigne and Taylor, 2008 Orth et al., 2008 Shi et al., 2008, 2011). Quiescent cells (cells that are in a temporary state of not dividing) or cycling cells that do not reach mitosis during drug exposure are spared. In this sense both drugs are examples of M phase–specific drugs, at least in cell culture. More classic phase-specific drugs include cytarabine, a nucleoside analogue that directly inhibits DNA replication, and methotrexate, an antimetabolite that prevents dTTP synthesis, both of which are S phase specific (Chabner et al., 2006). The “fractional kill” theory for chemotherapy was developed to try to explain why a single dose of a cell cycle phase–specific cytotoxic drug only kills a fixed fraction of cancer cells, necessitating multiple doses to eradicate the tumor (Berenbaum, 1972). According to this theory, only cells that pass through the relevant cell cycle phase when drug is present above its cytotoxic threshold are killed. It predicts a strong correlation between proliferation rate and drug sensitivity in both cancers and normal tissues. This prediction holds well for paclitaxel in tissue culture (Baguley et al., 1995). Data from treatment of human solid tumors are more mixed. A positive correlation between proliferation rate and clinical response was seen in breast cancer for mostly DNA-targeted chemotherapy (Amadori et al., 1997) but not for doctetaxel (Noguchi, 2006). Fractional kill theory engendered a keen interest in measuring cancer proliferation rates. Table 1 shows some typical values.

TABLE 1: Cell cycle kinetics in human tumors and tissues estimated by pulse labeling with 3 H-thymidine and by doubling time.

The ranges refer to median values reported in different studies. The range inside brackets refers to individual patient values in one large study. Data from Skipper and Perry (1970), Skipper (1971), Meyer et al. (1984), Lord (1992), Amadori et al. (1997), and Komlodi-Pasztor et al. (2011).

Table 1 and comparable data from a large literature illustrate that individual patient tumors exhibit large variation in proliferation rate, and there is also likely to be large variation between locations in a single tumor. Despite this variation, it is clear that median proliferation rates in breast tumors are much lower than in bone marrow, somewhat lower than in gut crypts, and much lower than in typical tissue culture lines. Given these data, it is not clear how a few doses of paclitaxel can “melt away” (to borrow a phrase I have heard from clinicians) a large, slow-growing tumor in a responsive patient if it kills only dividing cells. It is also unclear how any cytotoxic drug can have strong anticancer activity at the dose limit set by bone marrow and gut toxicity if relative proliferation rates are the only source of selectivity. These are not new questions—they were posed for DNA-directed drugs in the 1960s and 1970s (Skipper, 1971). I draw attention to them because they have not been answered, and in my view this means that we do not understand how cytotoxic drugs work as medicines. I also feel that many basic cell biologists have a naïve view of human cancers as proliferating as fast as HeLa cells in a dish, as I did until recently.

Paclitaxel has an advantage over DNA-directed drugs for discussion of the proliferation rate paradox because its actions on dividing cells generate morphological biomarkers that can be scored by microscopy (Figure 1). Mitotic arrest reports a positive response to the drug in a dividing cell. Multiple interphase micronuclei, resembling a bunch of grapes, report that a cell has passed through a defective mitosis in the presence of paclitaxel (Figure 1). This nuclear morphology arises because chromosomes are scattered when the cell slips out of mitotic arrest into G1, and separate nuclear envelopes re-form around small clusters of chromosomes. Nuclei do not fuse during interphase, so this morphology cannot be reversed unless the cell reenters mitosis. Mitotic arrest, visualized by conventional histology, was used to show that a fraction of the cells in a tumor arrest in mitosis before going on to die in diverse mouse (Milross et al., 1996) and human breast (Symmans et al., 2000) tumors treated with paclitaxel. The fraction of cells that arrest was lower in human tumors (1–6%) than in mouse tumors (5–25%), presumably reflecting lower proliferation rates. Figure 1 shows images of cells in mouse tumors responding to paclitaxel, visualized by intravital imaging of green fluorescent protein (GFP)–histone. We used this technology to track responses to a single dose of paclitaxel in a human xenograft tumor that is highly paclitaxel sensitive (Orth et al., 2011). A subset of tumor cells (<25%) underwent the typical response seen in tissue culture: mitotic arrest followed by exit into G1 with micronuclei and apoptosis either directly from mitotic arrest or following exit. The rest responded differently: proliferation and mitotic entry ceased, and mononucleated cells died out over many days, apparently without going through mitosis in drug. This proliferation block was not seen when we tracked the same cells responding to paclitaxel in culture, implying the existence of additional drug actions in the tumor environment that somehow target nondividing cells. To be optimistic, we can believe that this unexpected action of paclitaxel captures an important component of the clinical response. What might it be? We discuss four possibilities next and in Figure 2.

FIGURE 1: Chromatin morphology reports responses of dividing cancer cells to paclitaxel in a tumor. HT1080 human cancer cells expressing histone H2B-GFP were grown as xenograft tumors in window chambers in nude mice, treated with paclitaxel, and imaged by laser confocal microscopy. Cells that divided in drug proceeded from mitotic arrest to multiple micronuclei and apoptosis. Next to far right and far right, sequential images of the same cell from a movie. (From Orth et al., 2011.)

FIGURE 2: Potential actions of paclitaxel on tumor cells. Green arrows show cell cycle transitions. Red arrows show the only well-characterized drug action—killing cancer cells that enter mitosis. Blue arrows show hypothetical mechanisms for killing quiescent cancer cells that would provide solutions to the proliferation rate paradox.

Solution 1: Drug retention

Paclitaxel is retained in tumor cells for many days after it has been washed out of the circulation (e.g., Mori et al., 2006). It is thus possible that its only cytotoxic action is to kill cells that enter mitosis (Figure 2, red arrow) and that prolonged drug retention by quiescent cells is sufficient to kill them as they slowly enter mitosis. Drug retention cannot be solely responsible for the efficacy of paclitaxel in the HT1080 xenograft model discussed earlier because the majority of tumor cells appeared to die without passing through a drug-arrested mitosis (Orth et al., 2011). However, the relevance of this finding to responses in human tumors is unclear. Drug retention may be an important factor in clinical efficacy of microtubule-targeting drugs and could help resolve the proliferation rate paradox.

Solution 2: Paclitaxel kills quiescent cancer cells

This is the most straightforward explanation for death of nonproliferating cells in solid tumors. Quiescent cells contain dynamic microtubules, so they will certainly be perturbed by paclitaxel. The question is, does this perturbation kill them? Cancer cells in culture exposed to paclitaxel at therapeutically relevant concentrations rarely die unless they enter mitosis (Baguley et al., 1995 Gascoigne and Taylor, 2008), but perhaps quiescent cells are more sensitive in tumors? Some aspects of the tumor environment, such as nutrient and oxygen deprivation, promote cell death (Weinberg, 2007). Others, such as contact with extracellular matrix, promote survival (Weaver et al., 2002). Paclitaxel could act directly on quiescent cells to tip this balance toward cell death in the tumor environment. This would explain the activity of microtubule-targeting drugs and lack of activity of mitosis-specific drugs in human tumors (Komlodi-Pasztor et al., 2011). It would also explain the mitosis-independent cell death that we observed in the xenograft tumor model discussed earlier, although I am skeptical, given the lack of killing of quiescent cells by paclitaxel in tissue culture.

If a cytotoxic drug kills quiescent cells, why does it not destroy every tissue in the human body? The tumor environment could be proapoptotic, but in addition, cancer cells may be intrinsically apoptosis sensitive. Cancer cells are selected for resistance to apoptosis (Weinberg, 2007), so we might then expect cancer cells to be generally more apoptosis resistant than their normal counterparts when challenged with chemotherapy drugs. However, when responses to antimitotic drugs were compared in dividing cells in culture, most epithelial cancer cell lines underwent apoptosis more readily than noncancer immortalized lines and primary cells (Orth et al., 2008 Shi et al., 2008). Proliferating noncancer cells trend to enter a senescence-like state after exit from mitotic arrest rather than initiate apoptosis (Blagosklonny et al., 2006). By these measures, dividing cancer cells are often more apoptosis sensitive than dividing normal cells. Leukocytes, whether normal or cancer derived, are also highly prone to apoptosis during mitotic arrest, which may help account for the bone marrow toxicity of mitosis-specific drugs (Tang et al., 2011). Letai (2008) proposed the “mitochondrial priming” theory to account for enhanced apoptosis sensitivity of cancer cells. His idea is that whereas antiapoptotic pathways are often up-regulated in cancer, concurrent up-regulation of proapoptotic BH3-only BCL-2–family proteins often renders the cancer cell closer to the threshold of apoptosis than its normal counterpart. Concurrent up-regulation of proapoptotic and antiapoptotic regulators “primes” cancer cells to initiate an apoptotic response to chemotherapy drugs that inhibit antiapoptotic pathways. Some cancers evolve apoptosis resistance by mechanisms that cannot be reversed by drugs, such as complete loss of Bax and Bak, but this is less common than drug-reversible mechanisms (Deng et al., 2007). Normal cells survive in drug, or choose senescence over apoptosis, because they lack proapoptotic activation and are not primed. Pretreatment measurements of mitochondrial priming predict clinical responses to chemotherapy and might be useful for guiding treatment (Chonghaile et al., 2011).

Solution 3: Paclitaxel targets noncancer cells in the tumor

Because microtubules are present in most cells, paclitaxel must act on noncancer cells in tumors, including endothelial cells, stromal fibroblasts, and leukocytes (Figure 2). Some of these actions might be important for, and even central to, the therapeutic response.

Endothelium: Tumors depend on blood vessels for oxygen and nutrients, and microtubules play important roles in endothelial cells. Drugs that depolymerize microtubules, notably combretastatin, can promote tumor regression by damaging established blood vessels, with unexplained tumor selectivity (Kanthou and Tozer, 2009). Paclitaxel lacks comparable damaging effects on established endothelial barriers (Verin et al., 2001) but might still cause some kind of endothelial damage in tumors.

Stroma: We know little about how paclitaxel might affect tumor stromal cells and the signals they send.

Leukocytes: These cells depend on microtubules for many aspects of their biology, including organelle transport and chemotaxis. Paclitaxel has complex effects on leukocytes, and there is some evidence that it enhances the ability of the immune system to kill cancer cells (Javeed et al., 2009). Tumor-associated macrophages are very common in solid tumors, where they are believed to mostly help the cancer by enhancing tumor growth and metastasis (Coussens and Werb, 2002). Paclitaxel and other chemotherapy drugs could change this situation. Paclitaxel acts directly on mouse macrophages, in concert with inflammatory cytokines, to induce expression of inducible nitric oxide synthase (iNOS), which can act as a weapon to kill cancer cells (Manthey et al., 1994). Nitric oxide (NO) can react with superoxide (O2 − ) to form peroxynitrite (ONOO − ) when both iNOS and NADPH oxidase are activated in macrophages (Brown and Neher, 2010). Peroxynitrite is more cytotoxic than either nitric oxide or superoxide alone and could play a role in chemotherapy responses. Activated macrophages also secrete inflammatory cytokines that could kill tumor cells directly or summon cytotoxic NK cells. Induction of a cytotoxic phenotype in tumor macrophages by direct action of microtubule-targeting drugs could explain why they show greater antitumor activity than mitosis-specific drugs.

Solution 4: Bystander killing

By this I mean that a drug acts on a subset of cancer cells in the expected way, which for paclitaxel is to damage or kill cells that enter mitosis. Damaged or dead cells then send some new signal or cause some environment change that causes damage or death to neighboring cancer cells. Bystander killing could occur by direct cancer cell–to–cancer cell signaling. It could also occur indirectly, via the immune system or blood vessels (Figure 2, dotted blue line). Bystander effects are well known in radiation biology (Little, 2006). Irradiated cells can damage unirradiated neighbors by signals that are transmitted through gap junctions and by secreted factors. DNA damage triggers secretion of inflammatory cytokines, which comprise an important class of bystander signal that can act directly or indirectly via leukocytes (Prise and O'sullivan, 2009). All cytotoxic drugs, including mitosis-arresting drugs (Orth et al., 2011), cause DNA damage, so we should expect bystander effects in chemotherapy. Bystander killing cannot obviously explain differences between paclitaxel and kinesin-5 inhibitors unless paclitaxel is simply better at killing dividing cells or damaging their DNA, for which there is some cell culture evidence (Shi et al., 2008, 2011).

Bystander effects caused by inflammatory signaling are probably important in chemotherapy. A recent paper examined the response of a mouse tumor to a DNA-alkylating drug, where the primary drug-induced cell death mechanism was necrosis (Guerriero et al., 2011). Necrotic cell death caused release of the proinflammatory chromatin molecule HMGB1 (Andersson and Tracey, 2011). This induced massive recruitment and activation of innate immune cells, which was required for tumor regression. Because the drug was ineffective at promoting tumor regression in the absence of inflammatory signaling, tumor cells were presumably killed in large part by leukocytes as a bystander response. The primary drug-induced death mechanism in paclitaxel is apoptosis, which is less proinflammatory than necrosis. However, inflammatory signaling might result if the rate of apoptotic death overwhelmed phagocytic clean-up mechanisms (“secondary necrosis” Silva, 2010) or if tumor cells exit mitotic arrest into a senescence-like state (Blagosklonny et al., 2006) and this triggers cytokine release and immune clearance (Xue et al., 2007). Taxane treatment induces massive leukocyte recruitment to drug-responsive tumors in mice (Schimming et al., 1999) and humans (Demaria et al., 2001), but it is not clear whether the leukocytes are just cleaning up corpses or playing an active role in therapy. Combining these ideas with solution 3, I speculate that bystander signals from damaged cancer cells could combine with direct action of microtubule-targeting drugs on leukocytes to induce a tumor-killing inflammatory reaction (Figure 2, dotted blue arrow).

An extreme form of bystander effect is induction of adaptive immunity by dying cells. Kroemer, Zitvogel, and colleagues argue that the most effective cytotoxic agents may work by promoting “immunogenic cell death,” a sequence of cellular events that render dying cancer cells highly immunogenic (Kepp et al., 2011). Oxaliplatin is an effective trigger of immunogenic death in mice how paclitaxel acts in this respect is unclear. This exciting potential mechanism harnesses the full power of the immune system to reject the cancer, but its role in current chemotherapy is unclear.

An interesting aspect of bystander effects is their potential for positive feedback. If damage to one tumor cell triggers damage to more than one neighbor, a snowball effect could be set in motion that ends up killing entire tracts of the tumor. Getting this snowball rolling would presumably require some threshold level of direct cell killing by drug, so one could imagine that success versus failure of therapy is balanced on a knife edge. This could help explain large differences in response among patients with similar disease and the need for maximally tolerated drug doses.


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