Cell growth + division lecture 8

Question 1

Coordination of growth + division

Answer 1

• Need to link
• Certain factor triggers cells to grow then divide once certain size (yeast) vs other factors cause cells to divide in mammals

Question 2

Yeast

Coordination of growth + division

Answer 2

• Divide at same size
• If overexposes cyclins, G1 phase is shortened, enter S phase faster → smaller
• WT cell in nutrient poor phase gives small cells,

Question 3

S pombe

Coordination of growth + division

Answer 3

• Wee1 inhibited by Cdt1, both in midsize
• Pom1 in poles
• Short cells Pom1 = pole + diffuses away, conc in midsize ↑
• Pom1 inhibits Cdt1 so x inhibit wee1 (Cdk phosph + inactive)

Question 4

S cerevisiae

Sense size

Answer 4

• Small bud forms on surface of mother
• Cell cycle inhibitor Whi5 (like Rb)
• ↑ size cell = ↓ conc of Whi5 until reaches threshold → S
• If overexpress Whi5 → bigger cells

Question 5

Uncoupled proliferation + growth

Answer 5

• Egg/neurons have withdrawn from cycle but still grow?

- Schwan cells

Question 6

Increased cell size + faster cell cycle entry

Answer 6

• ↑ size = faster entry

- Drosphilia overexposes Rheb ↑ size ↓ G1 so ↑ growth rate

Question 7

TOR

Answer 7

• Many nutrient sensing systems activate mTORC1
• Tor = either mTOCR1 or mTORC2
• mTORC1 inhibited by rapamycin, prevents substrate access
• mTORC1 = raptor, mTORC2 = rictor
• mTORC1 = activated ds of IGF1 receptor (IGFR → Act → TSC1/2 inhibits → inhibits Rheb → reg mTORC1)
• mTORC1 phosph S6K =, inhibits 4E-BP
• Akt inhibits Tsc1/2 → Rheb-GTP → mTOR active
• AMPK activates TSC1/2 → Rheb-GDP

Question 8

mTORC1 stimulation of cell growth

Answer 8

• S6K activation → phosph SKAR → activation of e1F4 factors → ↑ protein synthesis
• S6k → activates SREBP → ↑ glucose metabolism
• Autophagy inhibited

Question 9

mTORC2

Answer 9

• phosph Akt, ↑ substrates in cell cycle
• phosph PKC (cytoskeleton rearrangement)
• Activates SGK promotes ion transport