Cell Cycle part 1

Question 1

What regulates organ and body size?

Answer 1

Cell division, cell growth, and cell death.

Question 2

What are the extracellular signals for cell growth, division and death?

Answer 2

Mitogens: stimulate cell division • Growth factors: Stimulate cell growth • Survival Factors: Promote cell survival by inhibiting apoptosis (cell death)

Question 3

What are the cell cycle phases and their roles?

Answer 3

M phase - includes mitosis (nuclear division) and cytokinesis (cytoplasmic division)
G1 phase - cell growth and monitoring conditions
S phase- DNA replication
G2 phase- cell growth and monitoring conditions

Question 4

What happens to the cell cycle when yeasts are shifted to a higher temperature?

Answer 4

The cell cycle is disrupted at a restrictive high temp, because the gene product required for progression for G1 to S is no longer functional. Differs from permissive low temp.

Question 5

Describe the cell cycle control system.

Answer 5

Checkpoints occur at start causing entry to cell cycle and proceeding to S phase.
G2/M checkpoint causes entry into mitosis.
Metaphase to Anaphase checkpoint triggers anaphase and proceeds to cytokinesis.

Question 6

What regulates the cell cycle control system?

Answer 6

Formation of Cyclin-Cdk Complexes along with

Transcriptional Regulation • • Phosphorylation/ Dephosphorylation • Protein Binding • Proteolysis/Degradation

Question 7

Describe Cyclin-Cdk complexes -

Answer 7

regulate cell cycle events. Cdk activites rise and fall throughout cell cycle but levels stay the same. Cyclins regulate activities of Cdks and direct them to target proteins.

Question 8

What are the major cyclin cdk complexes -

Answer 8

G1, G1/S, S, M Cdks

Question 9

What do G1 cyclins do?

Answer 9

They regulate G1/S cyclins, produce S cyclins.

Question 10

How is cdk regulated by cyclins?

Answer 10

Cyclin partially activates Cdk and Cdk activating kinase fully activates it.

Question 11

How is the cyclin cdk complex regulated by phosphorylation and dephosphorylation?

Answer 11

Wee 1 kinase adds a phosphate, inactivating the complex, Cdc 25 phosphatase removes the complex, activating the complex.

Question 12

How is the cyclin cdk complex regulated by protein binding?

Answer 12

p27 inactivates the complex.

Question 13

What does the SCF complex do?

Answer 13

Causes ubiquitination and degradation of Cdk inhibitor protein in proteasome.

Question 14

What does the anaphase promoting complex do?

Answer 14

Degrades m-cyclin, s-cyclin, and securin through ubiquitination.

Question 15

What are mitogens?

Answer 15

Extracellular signal that stimulates cell proliferation. • Activates Ras/MAPK pathway • Promotes expression of immediate early gene expression.

Question 16

What is the function of Myc -

Answer 16

important immediate early gene, increases expression of G1 cyclins, results in increased active G1-Cdk

Question 17

What does G1-Cdk do?

Answer 17

phosphorylates and inactivates Retinoblastoma (Rb), so E2F proteins can become active.
• E2F protein promotes transcription of G1/S- and S-cyclins for progression into S phase.
Positive feedback occurs when G1/S cdk is bound by G1/S cyclin, keeping Rb off and keeping E2F on.

Question 18

What does the E2F protein do?

Answer 18

It promotes transcription of G1/S and S cyclins for progression into S phase.

Question 19

What is the role of the S-Cdk complex?

Answer 19

It phosphorylates ORC and helicase to start dna replication.

Question 20

What do cohesins do?

Answer 20

Hold sister chromatids together along their length following DNA replication

Question 21

Describe centrosome duplication:

Answer 21

triggered by G1/S-Cdk, occurs during S phase.

Question 22

What is the role of the m-cdk complex?

Answer 22

Triggers assembly of condensin complexes for chromosome condensation • Induces separation of centrosomes and assembly of mitotic spindle • Ensures correct attachment of sister chromatids to the spindle • Breakdown of nuclear envelope (animal cells)

Question 23

What do condensins do?

Answer 23

Execute chromosome condensation.

Question 24

How is mitosis initiated?

Answer 24

Cdc25 activates M-cyclin via dephosphorylation.

It inhibits Wee1 through positive feedback and activates phosphatase through positive feedback.

Question 25

What is the role of M phase?

Answer 25

M Phase consists of mitosis and cytokinesis • Segregation of Chromosomes (correct #) • Production of daughter cells

Question 26

Describe prophase.

Answer 26

Sister Chromatids Condense • Mitotic Spindle begins to form outside nucleus

Question 27

Describe prometaphase

Answer 27

Breakdown of nuclear envelope.

Question 28

Describe metaphase

Answer 28

Chromosomes align at equator of spindle between the poles. • Chromosomes attach to the spindle.

Question 29

Describe anaphase

Answer 29

• Sister chromatids separate and are pulled toward the
spindle poles.
• Kinetochore microtubules shorten and spindle poles move
apart.

Question 30

Describe how the anaphase promoting complex works -

Answer 30

Cdc20 activates it, causing APC to ubiquinate securin, degrading it, and activating separase, which degrades cohesins holding sister chromatids together.

Question 31

Describe different parts of the mitotic spindle -

Answer 31

astral microtubules radiate to cortex, kinetochore microtubules attach to chromatids, and interpolar microtubules interdigitate between poles.

Question 32

Describe anaphase a and anaphase b -

Answer 32

anaphase a causes shortening of kinetochore microtubules and movement of daughter chromosomes to poles. anaphase b causes the poles to move apart.

Question 33

How are chromosomes pulled toward spindle poles?

Answer 33

They use energy from GTP hydrolysis occuring on tubulin subunits.

Question 34

Describe telophase -

Answer 34

chromosomes arrive at the poles of the spindle and decondense. Nuclear envelope reassembles.

Question 35

Describe cytokinesis -

Answer 35

Cytoplasm is divided in two by the action of the contractile ring.

Question 36

What causes contraction that pinches the cell?

Answer 36

Rho triggers actin formation and myosin activation to cause contraction.