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BIOB11H3 Lecture Notes - Kinetochore, Centrosome, Centromere

Biological Sciences
Course Code
Aarti Ashok

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The Cell Cycle
x Centromere
x Kinetochore
x Centrosome
x Chromosome
x Chromatid
An Overview of the Cell Cycle
x Cell division is required for a zygote to develop into an organism
x Go through 200-300 ell differentiation to become what we are
x Without cell division, we Á}v[Z}Ç
x Throughout our life, we need to renew tissues and cells (sometimes by minute basis, sometimes
by day basis)
x We need control of that process
o Need mitosis
o D]}]µo]vZo}]ooAvoo]v}U][]o}]
x Interphase is the majority of the time the cell spends its life
x Mitosis is a small segment, only a blip of the history of the cell
x Most of the time spent in G1, S, and G2 (phases of interphase)
x Cell cycle: stages that occur between one cell division and the next
x G1, S, and G2
x S phase = synthesis
x G = gap
x Follow my mitosis and cytokinesis
Cell Cycles in vivo
x 3 types of cells
1. Differentiated cells that do not divide
a. ***Specialized cells
b. No capacity to be replaced
c. E}µvP}]vP]À]]}vhd][o}l]vZ'ìP~Á in G1, exiting at G1, not
re-entering cell cycle produces differentiated cells that do not divide)
2. Cells that do not divide unless stimulated to do so by a signal
a. Absence of neighbouring cells (take out cells in an organ
b. Removing part of the liver induces cell division of [remaining liver cells]*********
c. Stimulus is lack of neighbouring cells, cells need to replenish organ and go into cell
division form
d. Were in G0, but re entered cell cycle by going back to G1
3. Cells that continually divide
a. Hematopoietic stem cells need to divide and differentiate

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b. RBC & WBC DO NOT divide, need to replace them for ocontinuous supply Æ need pre
cursor cell to first divide than differentiate
Control of Cell Cycle
x Cyclin dependent kinases (CDKs)
o *****the cy;clin proteins form one subunit of the CDKs
o *****=protein levels
x G1 cyclin rises in G1, M cyclin that rises during mitosis, etc...
x W}]voÀoZvPU}]voÀo]}v]v]v]uUÇ}µv]uP]vZ<Z[
vv}vZÇo]v][]À]ÇÁ]oo]e and fall depending on presence/absence of each
cyclin subunit
x Same cyclin can team up with multiple CDK
x CDKs are kinases = phorphorylate things
x Teamed up with kinase, will posphorylate certain protein, allows progression of phases to
x Binding of cyclin to cycin dependent kinase causes conformational change in the enzyme, allows
access of substrate to active site of the enzyme
x As soon as you assemble the cyclin t CDK complex, you shold be able to phosphorylate proteins
x Removes the phosphate group [added by Wee1}******
x Not active until almost entering mitosis
x Cdc25 -Æ Only active when cell is a certain size****** (on diagram)
x Mitotic cyclins peak at G2, BUT complex activated at boundary
x Gap of time between peak of G2 and start of M, during which the complex is formed, it is not
yet active
x Holds true in mammalian cycle as well
x Phosphorylation by CDK can be inhibitory and stimulatory depending on target
x Stop the process [and allow time for the abnormality to be fixed]******
x Genome damaged t }v[Ávo duplicate genome damage
x NO DNA duplication t nothing to separate
x Lined up in metaphase plate and be separated equally
x Will wait until duplication has occurred
x Checkpoint 1:
o Growth factors parent?
o Genome damaged?*************
x Internal stimulus t check whether genome has any damage
x Checpoint 2: properly duplicated genome or damage that has occurred to genome
x Checkpoint 3: chromosomes attached to splindle during M phase
x DNA damage [or unreplicated DNA]******
x Activate of master kinase (ATR) Æ a kinase so wil phosphorylate CHK 1 activation upon
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