3.7 Cell Cycle Flashcards
Motor proteins use ___ to power transport along the microtubule “railroad”
ATP
ATP binding makes actin ___ more easily at the ___ end
polymerize
+ end
___ enables cytokines
Contractile ring formation of overlapping actin and myosin filaments
ATPase activity increeases once bound in ___
Filaments
Myosin moves what?
Membranes or cell components
Muscle is contracted by
Actin and myosin
Most important cell cycle checkpoints:
Enter S phase
Enter Mitosis
Describe “enter S phase” check point
Is the environment favorable?
Is it ready to replicate?
Describe the “enter Mitosis” phase
Is all DNA replicated?
Is environment favorable?
Phosphorylation allows ___ signals to control ___ protein activity
Extracellular
Intracellular
Reversible covalent modifications turn proteins on, off, or both? What can do this?
Both
Kinase and phosphatase
Extracellular signals can control intracellular protein activity by activating ___ activators or ___
Allosteric activators or inhibitors
The cell cycle is controlled by ___
Cdk
Function of Cdk. How does it become active?
- Cdk phosphorylates cell targets that enter different parts of cell cycle
- Requires cyclin binding to form Cdk complexes (it allosterically binds)
How does Cdk become fully active?
Cdk-activating kinase (CAK) phosphorylates Cdk
G1-Cdk is a cyclin type for what role?
Advance G1
G1/S-Cdk is a cyclin for what phase?
Entry into S phase
S-Cdk is a cyclin for what phase?
DNA replication
M-Cdk is a cyclin for what phase?
Entry into mitosis
What are the 3 ways to control Cdk activity?
- Cyclin concentration
- Cdk phosphorylation controls activity
- Cdk inhibitor proteins can inhibit Cdk-cyclin complex formation (cyclin binding)
Explain the regulation of cyclin concentration
- Cyclin protein expression
- Degradation of existing cyclin
Explain how Cdk phosphorylation controls activity
Activating and inactivating kinases and phosphatases act on Cdk to regulate activity
___ control entry into S phase and mitosis
Mitogens
Steps for mitogen causing release of Myc
- Mitogen binds to receptor on plasma membrane
- Changes conformation and binds to accessory protein (Ras)
- Binds to MAP kinase
- Causes MAPK cascade
- Phosphorylates proteins that can go into nucleus and binds to immediate early genes
- Immediate early gene product binds to promoters of early genes
- Causes expression of genes (gene regulatory proteins like Myc)
- Myc causes expression of cyclins
lmmediate early genes expression upregulates transcription of ___
Delayed genes
The last protein that is phosphorylated by MAP kinase goes where?
Into the nucleus
What happens if you change the phosphorylation state of a Cdk?
It alters Cyclin/Cdk complex activity
Cdk is activated by
Phosphatase
Cdk is inactivated by
Kinase
___ transcription factor causes expression of genes that drive entry into ___ phase
E2F
S phase
___ holds E2F inactive until phosphorylated by G1-Cdk
Rb (retinoblastoma)
Steps for inactivation and activation of E2F
- Rb inhibits E2F activation
- G1 phosphorylates Rb
- E2F falls off
- E2F is active and starts S phase gene transcription
DNA damage halts cell cycle by activating ___
p53
p53 function
detects damaged DNA and stops it G1 from entering S phase in interphase, which prevents replication of bad DNA
p53 activates ___ to do what?
p21 gene, which encodes an inhibitory protein for G1 and S Cdks
What happens if p53 is mutated?
There are more damaged cells
- Malignant tumors have inactive p53
___ patches chromosome ends
Telomerase
Define telomerase
- Maintains chromosome length
- Has its own RNA template and keeps telomeres longer
