Cell cycle Flashcards
Cell cycle doctrine states “ “
-rudolf Virchow
“Every cell
comes from another cell.”
Times of cell cycle Early Frog embryo cells Yeast cells Intestinal epithelial cells Mammalian fibroblasts in culture Human liver cells
30 minutes 1.5 - 3.0 hours ~12 hours ~20 hours ~1 year
Moral: cell division times vary greatly
Phases of the cell cycle, start with m
m –> G1 –> S –> G2 –> m
m phase:
Stands for mitosis
takes < 1 hr in mammals
cytokinesis:
Cytoplasmic division: occurs near end of the M phase
s phase:
Stands for synthesis
DNA synthesized
Requires 10-12 hrs
G1 and G2:
Both involve growth monitoring intracellular conditions
Interphase:
G1, S, G2. Requres ~23 hrs
G(0)
specialized resting state, lasts days - years.
Many cells will stay in G0 permanently.
How far can a cell go and still pause? prophase pro-metaphase metaphase anaphase telophase
A cell can go to metaphase and still pause. Once the cell reaches anaphase it will divide.
Budding yeast:
- Forms a bud to divide.
- Bud will form after the start transition (G1-S transition).
- Bud will continue to grow until it divides
Budding yeast are what genus species.
Saccharomyces cerevisiae
Fission yeast
Used in traditional brewing (pombe swahli word for beer)
Fission yeast are what genus species.
Schizosaccharomyces pombe
Bromodeoxyuridine is what?
Is used for what?
IT is a flourascent dye and a thymadine analogue.
It will incorporated into new DNA, so it can identify which cells are in the S phase.
Arrange in order of duration in that phase.
G1
G2
S
M
FACS (fluorescence activated cell sorter = FACS)
- Cells given dye which stains DNA
- ran through a flow cytometer.
- Which stage of the cell cycle they are in is revealed
Which questions are asked during Start transition (G1-->S)
Is the environment favorable?
Which questions are asked during
G2/M transition
Is all DNA replicated?
Is the environment favorable?
Which questions are asked during
metaphase-to-anaphase transition?
Are all chromosomes attached to the spindle?
what does CCCS stand for?
The cell cycle control system.
Are CCCS protein actually involved in doing the work of dividing the cell?
NO
Evolutionary information of CCCS proteins.
- are evolutionarily conserved in eukaryotes.
- They are over 1 billion years old!
CDK stands for
Cyclin dependant kinase
kinases which require cyclin to work.
What causes the rise and fall of cyclin?
The flow between synthesis and degradation of cyclin.
While cyclin levels rise gradually, CDK activity increases ______. Once what has been reached?
Abruptly
The critical concentration of Cyclin
why did injecting cytoplasm
from an oocyte in M-phase into an unfertilized oocyte
induce the latter to enter into mitosis?
Because the cytoplasm of the M phase oocyte had the appropriate cyclin levels to make the cell enter M phase.
Frog oocytes are used for what reason?
Genus species.
They are large with lots of cytoplasm.
Xenopus Laevis.
G1-CDK does what?
promote passage through check point
G1/S-CDK does what?
Commits cell to DNA replication
M-CDK does what?
Promotes events of mitosis
S-CDK does what?
Required for initiation of DNA replicatoin
Which cyclin is used by this Cdk?
G1-CDK
G1-CDK : cyclin D
Which cyclin is used by this Cdk?
G1/S-CDK
G1-CDK : cyclin E
Which cyclin is used by this Cdk?
S-CDK
G1-CDK : cyclin A
Which cyclin is used by this Cdk?
M-CDK
G1-CDK : cyclin B
Each Cdk-cyclin complex phosphorylates ______ ______ ______.
Substrates of Cdk phosphorylation _____
or _____ major events in the cell cycle.
different protein substrates
initiate, regulate
Different Cdk-cyclin complexes are directed to different substrates by the _____ of the complex.
Different Cdk substrates may vary in ______ during the cell cycle.
cyclin component
availability
What does CAK stand for?
What does CAK do?
CAK stands for Cyclin activating complex.
SOME Cyclin-Cdk complexes are only partially active. CAK phosphorylates them in order to activate them.
M-CDK activity can be suppressed by what?
Phosphorylation by protein Kinase Wee1
Dephosphorylation of M-CDK to activate it is performed by?
dephosphorylation by protein phosphatase Cdc25
CKI stand for what?
Cdk- inhibitory proteins.
What doe CKIs do?
They bind to CDKs suppressing their activity
What is the primary control mechanism for regulation of Cdk activity?
Degradation of cyclin by proteasomes.
Define Polyubiquitination.
Adding of multiple ubiquitins.
Cyclin must be Polyubiquitinated in order to be destroyed. This happens systematically.
True.
Proteasome:
-Large multimeric ATP dependent protein which digests proteins in the cytosol.
Where in the proteasome is there actual protease activity?
In the center of the central 20S core proteasome. So protease activity is in the middle of the middle segment of the protease.
There are 19S caps on each side of the 20S core. How many proteins do they consist of?
~20
What is the function of the two 19S caps?
They selectively bind poly-ubiquitylated proteins.
They utilize ATP hydrolysis to unfold proteins and feed them into inner chamber for digestion into short peptides.
proteasomes
constitute nearly ___% of cellular protein.
Meaning they are ______.
1
highly abundant.
Proteasomes degrade ___% of newly synthesized proteins
33
How substantial
Covalently tagging
proteins with
ubiquitin is called ______ or ______.
ubiquination
ubiquitylation
What does the following ubiquination cause?
Monoubiquitylation:
Multipleubiquitylation:
Monoubiquitylation: a single ubiquitin
-histone regulation
Multipleubiquitylation: multiple single ubiquitins
-Endocytosis
What does the following ubiquination cause?
Polyubiquitylation
- lys48:
- Lys63:
- lys48: Proteasomal Degradation
- Lys63: DNA repair
Explain the real names of the 3 enzymes involved in ubiquitylation.
E1
E2
E3
E1: Ubiquitin-activating enzyme
E2: Ubiquitin-conjugating enzyme
E3: Ubiquitin ligase
Explain the 3 enzymes involved in ubiquitylation.
E1
E2
E3
ATP is hydrolyzed to transfer ubiquitin onto E1 (Ubiquitin-activating enzyme),
E1 it to a thiol on E2 (Ubiquitin-conjugating enzyme)
E2 combines with an E3 (Ubiquitin ligase) and adds ubiquitins.
Where in the E1, E2, E3 ubiquitylation process does enzymatic specificity occur?
E2 has several forms
E3 has many many forms
E2 and E3 decide specificity
Where in the E1, E2, E3 ubiquitylation process does enzymatic specificity occur?
E2 has several forms
E3 has many many forms
E2 and E3 decide specificity
Degron:
Degrons are built in signals in a protein which mark it for degradation by proteasomes.
What does having a degron do for a protein?
It limits it’s ability to act. Giving it temporal precision.
RGS4 is an example of what?
A degron. It is a gap for certain heterotrimeric G-proteins.
