TAMU BIOL 213 - Cell Cycle Control and Apoptosis (5 pages)

Previewing pages 1, 2 of 5 page document View the full content.
View Full Document

Cell Cycle Control and Apoptosis



Previewing pages 1, 2 of actual document.

View the full content.
View Full Document
View Full Document

Cell Cycle Control and Apoptosis

256 views


Lecture number:
24
Pages:
5
Type:
Lecture Note
School:
Texas A&M University
Course:
Biol 213 - Molecular Cell Biol
Edition:
1
Unformatted text preview:

BIOL 213 1st Edition Lecture 24 Outline of Last Lecture I Cyclic AMP a Produced by adenylyl cyclase b Primary target is PKA II Inositol triphosphate IP3 diacylglycerol DAG and Ca2 a IP3 and DAG are generated by phospholipase C b IP3 opens Ca2 channels in the ER and Ca2 and DAG activate PKC c Ca2 can bind to other proteins like calmodulin which can then bind to CaMkinase III Enzyme linked receptors a Receptor tyrosine kinases activate signaling proteins b PIP3 c Ras IV Some pathways are activated only if multiple signals are present V Review VI Plant signaling VII Receptor downregulation Outline of Current Lecture I Eukaryotic cell cycle a Four phases II III IV b Regulation was discovered by observing mitosis of Xenopus frog eggs Cyclin and Cdks control progression through the cell cycle a M cyclin binds to Cdk to create an M Cdk b The sharp decrease in levels of M cyclin after M phase is due to degradation of cyclin by proteasomes S Phase DNA replication G1 phase arrest due to DNA damage These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute V a Outline If DNA damage is detected p53 will be activated which will initiate transcription of the p21 gene The p21 protein a Cdk will bind to the active SCdk and inactivate it so that S phase cannot be initiated Apoptosis programmed cell death a It s mediated by an intracellular proteolytic cascade that cuts the cell up into nice little pieces b High stress to the p53 protein causes the p53 to induce apoptosis Current Lecture I Eukaryotic cell cycle a Four phases i G1 phase cell growth ii S phase DNA replication iii G2 phase cell growth iv M phase mitosis and cytokinesis b Internal and external conditions are monitored during the G1 and G2 phase i If any of these conditions aren t met signals in the cell stop it from going through mitosis ii G1 checkpoint 1 Right before the cell goes into the S phase 2 It checks external conditions a such as whether or not the environment is favorable b If the nutrients necessary and or signals for replication aren t there the cell doesn t go through replication 3 It checks internal conditions a Such as whether or not the DNA is intact b If the DNA isn t intact the cell doesn t want to replicate it iii G2 checkpoint 1 Right before the cell goes through mitosis 2 Checks to see if the DNA is intact and fully and properly replicated c The cell cycle can be arrested at multiple checkpoints d Some cells can forever stop dividing and enter the G0 phase i Cells in the G0 phase never divide ii Cyclin is completely shut of iii Ex neurons skeletal muscles e Regulation was discovered by observing mitosis of Xenopus frog eggs i These eggs are really big so that they can be seen in a microscope and they go through mitosis quickly ii Cytoplasm from an egg going through mitosis was injected into an oocyte 1 Oocyte immature precursor of an unfertilized egg 2 The oocyte was driven into M phase II iii Cytoplasm from an egg in interphase G1 S and G2 was injected into an oocyte 1 The oocyte was NOT driven into M phase iv They found that something in the cytoplasm of an egg going through M phase somehow initiates M phase They fractionated the cytoplasm to determine what the specific protein was 1 They ran the cytoplasm over one column so that a specific kind of protein remained bonded to the column while the other kinds ran past the column and were collected separately a Ex a negatively charged column would bond and hold to the positively charged proteins while the negatively proteins could be collected 2 The diferent solutions were run over other columns with diferent chemistry so that the protein that induced M phase was finally determined cyclin Cyclin and Cdks control progression through the cell cycle a Cyclin dependent kinases Cdks are proteins that are activated and inactivated by phosphorylation and dephosphorylation b Their concentration in the cell is constant throughout the entire cell cycle c They bind to cyclin d The concentration of cyclin varies throughout the cell cycle i It steadily increases during interphase is at its highest during M phase and drastically decreases at the end of M phase e M cyclin binds to Cdk to create an M Cdk i Initially the M Cdk is inactive ii An inhibitory kinase and an activating kinase each phosphorylate the Cdk iii The inhibitory phosphate and activating phosphate cancel each other out so that the M Cdk is still inactive iv Activating phosphatase cuts of the inhibitory phosphate so that the MCdk is active 1 Activating phosphatase is activated by active M Cdk v Active M Cdk initiates M phase 1 This activates activating phosphatase 2 This is a positive feedback loop vi Therefore the level of cyclin determines the progression through the cell cycle vii Eventually the amount of active M Cdk will be just enough more than the inactive M Cdk so that it will cause a cascade of activation of other MCdks and cause mitosis 1 This is amplification f III IV V The sharp decrease in levels of M cyclin after M phase is due to degradation of cyclin by proteasomes i Active M Cdks activate a protein that ubiquitinates the M cyclin 1 Ubiquitin is the protein that tags proteins for degradation by proteasomes 2 This is negative feedback g Each phase of the cell cycle has its own unique cyclin and Cdk i Ex S phase has an S cyclin and S Cdk ii The mechanism is basically the same iii The activated S Cdk triggers DNA replication machinery S Phase DNA replication a How is the DNA not replicated several times b As soon as DNA replication is started the signal protein that initiated replication is degraded c An origin recognition complex ORC sits on the origin of replication d An inactive Cdc6 is bonded to the ORC e S Cdk phosphorylates Cdc6 i This activates it which activates the ORC to initiate replication f Soon after the ORC initiates replication Cdc6 is degraded i This prevents re initiation G1 phase arrest due to DNA damage a Outline If DNA damage is detected p53 will be activated which will initiate transcription of the p21 gene The p21 protein a Cdk will bind to the active SCdk and inactivate it so that S phase cannot be initiated b There are always proteins scanning the DNA for damage c If damage is detected a protein kinase will be activated d This will activate a p53 protein by phosphorylation i Inactive p53s are degraded by proteasomes e The activated p53 will bind to the regulatory region of the p21


View Full Document

Access the best Study Guides, Lecture Notes and Practice Exams

Loading Unlocking...
Login

Join to view Cell Cycle Control and Apoptosis and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Cell Cycle Control and Apoptosis and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?