Exam 4 (1)

Question 1

Definition of G1

Answer 1

Period between previous divisions and initiation of DNA synthesis –> Cell is growing

Question 2

Definition of S

Answer 2

DNA/Chromosome Replication

Question 3

Definition of G2

Answer 3

Period between completion of DNA replication + Mitosis

Question 4

Definition of M

Answer 4

Nuclear Division (Mitosis) and Cytoplasmic Division (Cytokinesis)

Question 5

Special Divergence from G1?

Answer 5

G0: resting state for cells (quiescence); time where differentiation processes could take place

Question 6

How is it ensured that everything in each step of the cell cycle goes correctly? That we do not move on with some error?

Answer 6

Checkpoints: Coordinated Gene Expression and Signalling Events

Question 7

Pathway that governs G1 Cell Growth

Answer 7

Phosphotidylinositol 3-Kinase Pathway [PI3K]

Question 8

The 6 Steps of Pathway that governs G1 Cell Growth

Answer 8

Phosphotidylinositol 3-Kinase Pathway [PI3K]

1. Growth Factors induce dimerization of Receptor Tyrosine Kinases (Cross-Phosphorylation)
2. RTKs phosphorylate/activate PI3Ks (anchor on phospho-tyrosine residues; in close proximity to cytosolic phospholipids)
3. Activated PI3K phosphorylates the 3’ position of phosphotidylinositol, yielding PI(3,4,5)P3, along with other phosphotidylinositides
4. Accumulation of PI(3,4,5)P3 lends to activation of Akt (Serine Threonine Kinase)
5. Akt activates mTOR (protein kinase for cell growth) + other proteins
6. mTOR phosphorylates (i) gene-regulatory factors –> ribosome synthesis –> proteins/growth!
   (ii) S6-Kinase –> phosphorylates S6 (protein on ribosome) –> increase mRNA translations
   (iii) 4E-BP (inhibits eIF4e) –> releases eIF4e (translation initiation factor) –> translation initiated