kiss cell cycle Flashcards
what is the cytoplasm, and what is the cytosol?
Where is PDH, and what does it commit?
Cytoplasm is everything outside of the nucleus including organelles
* Cytosol is the cytoplasm minus the organelles
-PDH is in the mitochondria and commits pyruvate to the citric acid cycle
What does PDH bring in?
What does it convert?
must bring in the pyruvate (thus we must use the pyruvate shuttle to pump pyruvate into the
mitochondria)
* pyruvate is converted into acetyl CoA, by the enzyme PDH
How is PDH regulated?
What stimulates PDH
What is another method of PDH regulation?
-PDH is regulated via hormones (ie. insulin). Insulin would stimulate PDH bc when there is a lot of glucose PDH would want to act to convert glucose to energy
-PDH is also regulated via phosphorylation -> phosphorylated PDH is mediated via PDK (pyruvate dehydrogenase kinase)
What does phosphorlyation of PDH lead to?
What reactivates PDH, and what does insulin activate?
Phosprylation of PDH leads to inactivity, phosphatase (PDK) removes the phosphate and reactivates the PDH
-Insulin activates the phosphatase to lead to the activation of PDH
What does PDK inactivate?
What does PDP activate, what does it stand for?
-what is PDP activated by?
PDK inactivates PDH and PDP which activates PDH. -PDP (pyruvate dehydrogenase phosphatase) is activated by insulin to promote the degredation of glucose and turn it into acetyl CoA to go into the
citric acid cycle or be stored as a fatty acid
What is the rate limiting step of fatty acids (lipogenesis)?
What does insulin activate, and what happens to ACC in dephosphorlytion?
it is an enzyme called ACC
-Insulin activates a phosphatase (ACC phosphatase) so by dephosphorylation ACC insulin is promoting/ driving the pathway. Bc PDH (glycolysis) has pyruvate -> acetyl CoA by activating pyruvate dehydrogenase phosphatases (PDP)
What are the 2 pathways that insullin can activate?
-can activate Acetyl CoA formation by PDP (pyruvate dehydrogenase phosphatase) (glycolysis)
-can also activate formation of fatty acids by ACC-P (lipogenesis)
What is the S phase and the M phase?
What is the g phase, where is it?
-s phase=cell duplicating into DNA
-M phase=time to split (separate chromosomes), includes mitosis and cytokinesis
G1 is before S phase and is the receovery phase
G2 is the waiting phase and is before the M phase
What are the components of M phase specifically mitosis?
PPMAT
P-prophase
P-prometaphase
M-metaphase
A-anaphase
T-telphase
What does cyclin CDK control?
What do CDK depend on to carry out activity, what happens to it when its jobis over?
MANY CYCLIN CDK -> ONE CONTROLS M PHASE (MCDK)
-These are the master kinases that regulate major transition events in the cell cycle
-they depend on cyclin, once job of cyclin is over it gets degraded
What is each cyclin specific for?
-specific for a certain phase
How does CDK get activated by cyclin?
What does cyclin change?
CDK ( ATP binding protein), just there, we do not need ATP energy it just binds it
* When cyclin comes along it changes the conformation of a specific loop in the CDK ( the T loop) the active site of the enzyme
What does CAK do after CDK is partially active?
when a CAK comes along it phosphorylates CDK on a certain location and now CDK is active (CDK needs to bind ATP, cyclin, and CAK)
What occurs at the 2nd phoshphorylation in CDK?
What is the 2nd kinase, what does it control?
when a second kinase (Wee1) comes along and phosphorylates CDK at a second site it inhibits it, thus no matter what state the CDK is in (whether the first activation phosphorylation has occurred or not), by the second site being phosphorylated this
CDK is inactive
-Thus Wee1 controls the activation of CDK cyclin
What does CDC 25 contol, what is it?
Cdc25 is a phosphatase that dephosphorylates this specific phosphate on the CDK leading to an active CDK cyclin complex
* Wee1 and Cdc25 are in competition
what are teh 2 methods that can inactiavte CDK cyclin?
Now another protein p27 comes and wraps around cyclin and CDK which produces an inactive protein
-Thus 2 methods to inactivate CDK cyclin: phosphorylate the inhibiting site with Wee 1 kinase or wrap p27 around it
What are the components of PP2A and what is its job?
- (PP2A= protein phosphate 2A) had 3 subunits: alpha, beta, gamma.
-Catalytic, regulatory,scaffold -> form a heterotrimer - The job is to dephosphorylate and counter activity of kinases
What inhibits PP2A?
What form if PP2A is inactive vs active?
What does the inactive form of PP2A stop?
-ensa is phosphor. by great wall kinase, phosphorlyated ensa inhibts PP2A
-phosphor. PP2A is inactive
-dephosphor. PP2A is active
-can prevent mitosis from occuring
What activates MCDK?
What does MCDK activate?
-MCDK is activated by proper phosphor. at the correct site
-active MDCK activates greatwall kinase?
How does MCDK interact with PP2A/
-it inhibits PP2A by activating great wall kinase which phosphorlyates Ensa, which acts as an allosteric inhibitor of PP2A
What does CDK1 associatye with, and what goes on the activating site and inhibitory site?
Cdk1 associates with M-cyclin as the levels of M-cyclin gradually rise.
-The resulting M-Cdk complex is phosphorylated on an activating site by Cdk-activating kinase (CAK) and on a pair of inhibitory sites by Wee1 kinase
When and what actiavtes MCDK in the positive feedback mechanism?
The resulting inactive M-Cdk complex is then activated at the end of G2 by the phosphatase Cdc25.
-Cdc25 is further stimulated by active M-Cdk, resulting in positive feedback.
How is the positive feedback mechanism enhanced?
how does active M-CDK lead to inihitbion of wee1?
This feedback is enhanced by the ability of M-Cdk to inhibit Wee1
-active M-CDK leads to PP2A dephosphorylating Wee1 (allowing more MCDK activity since phosphor wee 1 inihibits MCDK)
If we inhibited CAK how would that affect the activity of MCDK?
What if we inihibted CDC25?
-it would mean the phosphor sites never get phosphorylated, thus MCDK never gets activated
-If CDC25 was inhibted, inhibitory phosphate would always be present and MCDK would never become active
WHat is APC/C?
What is the activating subunit of APC/C?
What does activation of APC/C lead to?
APC/C is anaphase promoting complex/cyclosome and it is an E3 Ub ligase
-Cdc 20
-active APC/C, which is an E3 Ub ligase of CDK cyclin, leads to proteasomal degradation
What activates APC-C?
What does an active APC/C-CDC20 lead to?
M-Cdk phosphorylates the APC/C, thereby enhancing its association with Cdc20
-APC/C–Cdc20 also turns itself off by inactivating Cdks, which allows APC/C dephosphorylation. APC/C–Cdc20 is thereby inactivated in anaphase.
How does cdh1 remain inactive?
what causes its activation?
-active M-CDK keeps cdh1 inactive
-When cyclins are destroyed in anaphase, Cdk inactivation allows Cdh1 dephosphorylation, which activates Cdh1 and thereby stimulates formation of APC/C–Cdh1
When does binding MT increase (in what direction of movement?
Why does length of MT not change much?
-as we move towards the spindle pole kinetochore center
-the length of a kinetochore microtubule does not change much because new tubulin subunits are added at the microtubule plus end at the same rate as tubulin subunits are removed from the minus end.
What happens to securin when we activate APC/C?
The activation of APC/C by Cdc20 leads to the ubiquitylation and destruction of securin, which normally holds separase in an inactive state
What does the destruction of securin cause?
destruction of securin allows separase to cleave Scc1, a subunit of the cohesin complex holding the sister chromatids together, allowing the final separation in anaphase to occur
What activates and in activates RhoA in the regulation of contractile ring for cytokinesis?
What is the activator for Rho GEF
RhoA is activated by a Rho GEF protein (called Ect2) and inactivated by a Rho GTPase-activating protein (Rho GAP)
-RhoA at the future cleavage site depends on Ect2 activation by another protein complex called centralspindlin, which comes frmo aurora B
What happens after RhoA is activated, what are the 2 pathways?
pathway 1:it binds to formins, and activated RhoA promotes the assembly of actin filaments in the contractile ring.
pathway 2: By activating Rho-associated protein kinases, such as ROCK, it stimulates myosin II filament formation and activity, thereby promoting contraction of the ring.
What leads to activation of MTORC1 pathway?
occupation of cell-surface receptors by growth factors or by cytosolic amino acids leads to the activation of a complex signaling pathway that results in the activation of the multisubunit protein kinase mTORC1
What are the first 2 things that mTORC1 stimulates in the pathway?
mTORC1 phosphorylates multiple proteins, including 4EBP and the protein kinase S6 kinase 1 (S6K1), to stimulate the activity of the translation initiation factors eIF4E and eIF4B (respectively), thereby stimulating protein synthesis
What are the last 2 pathways that mTORC1 can activate, what does each one lead to?
mTORC1 also acts through S6Kinase 1and Lipin, to activate a transcription regulator called SREBP, which increases the expression of genes involved in lipid synthesis.
-Finally, mTORC1 phosphorylates another protein kinase, Ulk1, reducing its ability to promote protein turnover.
