Please enable JavaScript.
Coggle requires JavaScript to display documents.
The cell cycle - Coggle Diagram
The cell cycle
cell phases
S
DNA replication
G2
preparation of chromosome segregation and division
G1
cells grows and the time of this phase varies
where most cells enter cell arrest (G0)
M
chromatin condenses
nuclear envelope breakdown
sister chromatids attach to mitotic spindles and segregate
chromatin decondense and the nuclei reforms before undergoing cytokinesis
can be further divided
prophase
metaphase
anaphase
telophase
G1-G2 is interphase
not much observable change occurs during this time
functions of the cell cycle
to ensure reproduction and passing on genetic information down to the next generation
to ensure the DNA in each chromosome is replicated properly to make 2 copies
to ensure the 2 chromosomes are distributed evenly to 2 genetically identical daughter cells
coordinates the growth/cell mass of the cell with division (ensure cell is big enough to divide/move to next phase)
cell division cycle mutants (cdc)
in both yeast, a temp sensitive mutant exist that stops the cell cycle when the temperature is reached
when cdc2 in S.pombe was lost, it prevented the transition of cell cycle phase from G2 to M
cdc2 is a cyclin dependent kinase
cdc2 is homologous to cdc28 in S.cerevisiae
if problem occurred to either cdc, could rescue with human yeast CDK
suggests that the proteins that control cell cycle in eukaryotes are highly conserved
discovery of 3 key regulators of cell cycle
kinases
adds a phosphate
phosphatases
removes phosphate
cyclins
cell cycle of S. cerevisiae
during division, a bud is formed
this bud indicates the stage of the cell cycle depending on it's size
they have a longer G1 phase
Cell cycle of S.pombe
elongation of ends indicate the cell cycle phase
to undergo cytokinesis, a septum wall is formed separating them
functioning of of CDK (cdc2)
cdc levels remained constant
another protein, mitotic cyclin peaks at G2 and falls off in M phase
mitotic cyclin activates cdc2 (CDK) and forms a heterodimer with it called the MPF
determined that cyclin regulates the amount of CDK expression
cyclin and cdc have strong correlation at times of expression, but not perfectly match as CDK is only PARTIALLY regulated by cyclin
cyclin dependent regulation of cell cycle
cyclins activate CDK
the cyclin present matches the stage of the cell cycle
G1 cyclins
G1/S cyclins
S cyclins
mitotic cyclins
cyclins are regulated on the transcription level and ubiquitin-mediated proteasome for degradation
ubiquitin mediated degradation of cyclin
Ub is a 76 aa protein found in all euk. cells that signals a target protein to be degraded
how it works
ubiquitin ligase has 2 separate sites, 1 for the target protein, other for the Ub conj enzyme
the Ub conj enzyme attaches Ub onto the target protein
the Ub signals signals 26S protease to degrade the protein where the Ub will be recycled for future use
regulation of MPF through phosphorylation
Cdc25
if too little Cdc25, phosphate is not removed, preventing entry to M phase
Too much Cdc25 causes the cell to rush through G2 and divide early without bulking up enough
Is an activator phosphatase that removes the inhibitory phosphate that causes CDK to become active
Wee1
if too much Wee1, phosphate is not removed, preventing entry to M phase
Too little Wee1 causes the cell to rush through G2 and divide early without bulking up enough
is a inhibitory kinase that phosphorylates CDK, stopping it's activation
prevents the early CDK activity
tyrosine 15 and threonine 161 are responsible for MPF activity
CDK
adds a phosphate to threonine 161 to activate CDK (NOT an inhib. phosphate)
is an activating kinase
Max activation when Wee1 not prevent, CAK added phosphate and Cdc removed phosphate at tyrosine 15
activated MPF causes more phosphorylation
can cause chromosome condensation
can disassemble nuclear envelope
microtubule disassembly during interphase and formation of mitotic spindle fibers
remodeling the Goli + ER to shut them down during cell division
turning off MPF
prevents cell to enter another cell cycle
cyclin has a 9 aa destruction both recognized by APC/C, Ub ligase
APC/C causes polyubiquination
Ub marks the cyclin to be degraded for proteolytic degradation with proteosomes
MPF activity drops and cell returns to interphase
regulation of S phase entry
S phase cyclin with CDK is normally supressed by an inhibitor until S phase
G1/S associated with CDK complex causes the inhibitor to be phosphorylated
phosphorylation causes the inhibitor to be marked by SCF to be degraded through polyubiquination
with no inhibitor, the S phase cyclin and CDK complex can be activated, helping with DNA replication
SCF acts to activate S phase CDK and degrading G1 phase cyclins as well as S phase cyclins