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Lecture 16

Biochemistry- Lecture 16(with chapter).docx

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BCHM 2021
Julie Clark

Biochemistry- Lecture 16 Cell Cycle - All cells come from pre-existing cells. -Cell cycle  cycle of cell growth and division -replicate t he chromosome -and segregated to the daughter cells -replicate the organelles  grow and duplicate  these have to get segregated to the daughter cells -increase in mass so that the cells are coordinated with the division -if we don’t want the cells to get smaller and smaller -S-phase= DNA synthesis -chromosome duplication -M-phase = segregation and cell division -segregation = mitosis -cell division= cytokinesis -there are 4 phases: -gap = G1 and G2 -time for growth and monitor environment  see if conditions are favourable to go ahead -the cell cycle = G1  S  G2  M  G1 -G0= resting phase -exit from G1  G 0 -end of G1= start -commitment to divide  irreversible -G1 + S + G2 = interphase  and then you have mitosis **video- 17.4-Animal Cell Division** **panel 17.1** Principles of Cell Cycle Control -these principles are similar in all eukaryotes  similar proteins found in all organisms -use model organisms -some of the genes comes from the yeast mutants  “cdc mutant”  “cell division cycle” -originally developed in yeast Question: The budding yeast and the fission yeast are sued to study many cellular processes because of their genetics. If cell-cycle progression is essential for cell viability in these yeasts, how is it possible to isolate cells that are defective in cell-cycle genes? Answer: A yeast mutant that is defective in a cell-cycle gene can be isolated if its phenotype is conditionally defective- that is, it can isolated if the product of the mutant gene fails to function under one set of conditions, but functions adequately under another. Most conditional cell-cycle mutants are temperature sensitive; the mutant protein fails to function at high temperature, but performs well enough at low temperature to allow cell division. -Checkpoints: 1) Start= entering the cell cycle proceeds to the S-phase after this point -looks to see if the conditions are favourable -monitor the environment 2)G2/M = enters into mitosis does not stop  if something goes wrong in S-phase = needs to get checked -checks if DNA synthesis is completed appropriated -monitor the environment 3)Metaphase/Anaphase Transition= are the chromosomes attached to the spindle? -spindle attachment check These checkpoints are biochemical switches that initiates the events of the cell cycle and will block the progress if there is a problem. -It checks for a favourable environment to see if the cell should grow forward. The cell cycle cannot go back. -Many of these steps are controlled by cyclin-dependent kineses. Cyclin-Dependent KInases -these are protein kinases=cdk -cyclical changes in the activity of the cdk  drives many events of the cell cycle -active at some points and inactive at other -cyclin is a protein activator of cdks -these are called cyclin their levels go up and down at various points -cylical changes in cyclin levels  these will cause changes in the cdk activity -if there is no cyclin = inactive enzyme -change cyclin and this will change the activity -each cyclin-cdk phosphorylates different substrates **this is a very important figure** Classes of Cyclins 1) G1-cdk: -control the activity of the G1/S cdk -not in all cells 2) G1/S-cdk
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