Cell cycle

Question 1

normal cell replication depends on…

Answer 1

1. Mitogens (growth factors)
2. anchors (must be anchored to ECM)
3. Contact w/ other cells (contact-inhibited, won’t divide if too crowded)
4. # of previous divisions (cells = mortal!)

Question 2

2 basic functions of cell cycle

Answer 2

1. make 2 copies of all genetic info (DNA duplication)

2. get entire genome to each daughter cell (chromosomal segregation)

Question 3

S phase of cell cycle

Answer 3

replication of DNA/chromosomes

Long time (almost half of whole cell cycle), 
*part of interphase

Question 4

M phase of cell cycle

Answer 4

mitosis (nucleus divides) 
and cytokinesis (cell contents separate)

• lasts ~ 1 hour out of 24 hr cycle!

Question 5

“Restriction Point”

Answer 5

the checkpoint at end of G1 phase.
where cell determines whether has enough GF and size to replicate
(if not, stays in phase –> “Go”)

Question 6

Major cell cycle checkpoints

(4)

Answer 6

1. restriction point (end of G1): to divide or not to divide?
2. S phase checkpoint: is DNA is damaged, and not fixable?
3. G2/M checkpoint: is replication completed?
4. Spindle assembly checkpoint (M): are chromatids properly arranged on spindles?

Question 7

Cyclins (types)

Answer 7

Cdk-activating proteins, no separate activity.
4 types:
(needed to pass through checkpoints in each phase of cell cycle)
A = S-cyclins, B = M-cyclins, D = G1-cyclins, E = G1S cyclins

Question 8

regulation of Cdk activity

Answer 8

1. degrade the cyclin (or the Cdk in some cases)
2. (de)phosphorylate
3. Cdk-interfering proteins (CKIs, CIPs, INKs)
4. transcriptional regulation (of cyclins, CKI, etc.)

Question 9

Activation of M-Cdk

Answer 9

1. Mitotic cyclin and CDK bind/complex
2. Wee-1 – adds P to complex
3. CAK – adds 2nd P to complex
4. Cdc25 activates the complex (removes 1 P, opens substrate binding site)

Question 10

CKI

Answer 10

Inhibitory molec for Cdks, binds to Cdk-cyclin complex;
wraps around so cannot f(x),
(regardless of what other molecs = present)

• counteracted by SCF proteosome

Question 11

cyclin D-Cdk

Answer 11

needed by ALL cells, EXCEPT for Embryonic Stem Cells (“ES”),
to pass restriction point.

–> concern: stem cells = naturally tumorigenic (!)

Question 12

needed for cell cycle “clock”

initiation and progression

Answer 12

outside signals:

• Tyrosine Kinase Rs
• GPCRs
• TGF-B Rs
• NRs AND: nutrient status (will not divide if cell = starving)

Question 13

G1 checkpoint decision (“regulation point”)

Answer 13

• -> divide (onto S phase) or not divide (to Go phase)
  1. external mitogenic signals –> “we need more cells”
  2. DNA damage??
  3. cell has grown enough?

Question 14

Mitogens that stimulate D-Cyclins (–> cell proliferation)

Answer 14

1. Growth factor (via Ras or HERneu…)
2. Wnt pathway
3. cytkines
4. NRs
5. Hedgehog

Question 15

SCF ubiquitin ligase

Answer 15

cell cycle reg. enzyme –> marks CKI for degradation

• • SCF indirectly promotes cell cycle progression **
    1. phosphorylates CKI
    2. CKI = poly-ubiquitinated (by ubiquitin)
• -> CKI = degraded

Question 16

TGF-Beta as tumor suppressor

pathways to inhibiting cell prolif.

Answer 16

3 ways to inhibit cell proliferation: (at restriction point)

1. increase expression of CKIs
2. Block phosphorylation of Rb
3. Prevent Myc expression

Question 17

Rb protein

Answer 17

regulates cell cycle (inhibits progression) by inhibiting EF2
(EF2 = gene enhancer —> + cell prolif.)
* need >1 phosphorylations of Rb to release from EF2
(phosphorylated by Myc)

Question 18

Contribution of Myc to cell cycle regulation

Answer 18

1. increases phosphorylation of Rb (–> frees EF2)

2. promotes expression of EF2

Question 19

what’s different in Embryonic stem cells for G1 checkpoint?

Answer 19

1. Rb = hyperphosphorylated (–> INactive)
2. no need for Mitogens
3. no DNA damage check
4. Cyclin E = constantly present (NOT degraded)
   - –> can blow through checkpoint w/o actual check!

Question 20

check against mitogen over-stimulation

Answer 20

1. feedback from mitogen stimulation –> Arf (chaperone protein)
2. Arf sequesters MDM2

*Arf = “14-3-3” (also = Raf inhibitor!)

Question 21

Types of functional mutations in genes to cause cancer

Answer 21

1. bypass need for mitogens
   (act: RTKs, Ras, Cyclin D, PI-3K; INact: PTEN, p53, TFG-Beta)
2. targeting G1 checkpoints
   (inhibit Rb, p53, CKIs; increase Myc/AP-1)
3. suppress apoptosis (act: PI-3K; INact: PTEN, p53)

Question 22

Dominant vs. Recessive mutations

Answer 22

Dominant: only need mutation in 1 allele

Recessive: must have same mutation in both alleles to exhibit mutation in f(x)

Question 23

Main ways to convert proto-oncogene to oncogene

Answer 23

1. Deletion in DNA – coding gene OR regulatory sequence
2. mut. transcr. machinery –> change gene expression
3. Chromosomal rearrangement
   - new reg. sequence
   - fusion to active transcr. gene –> hyperexpression!

Question 24

Most common causes of conversion of proto-oncogene to oncogene

Answer 24

1. Val –> glut (missense mut): no need for mitogens!
2. single deletion alters transmembrane domain of protein
   - -> R dimerizes w/o ligand!

Question 25

Philadelphia chromosome

Answer 25

translocation of tips of chromosomes 9 and 22 --> BCR-ABL fusion protein (constitutively active tyrosine kinase) ** causes CML (chronic myelogenous leukemia) if in bone marrow

Question 26

Imatinib/gleevac

Answer 26

a drug used to treat CML (chronic myelogenous leukemia), * * specifically targets cancer cells - -> no side effects!

Question 27

ways to have normal allele eliminated in heterozygote, | resulting in oncogene expression

Answer 27

* * usually = LOH ** 1. non-disjunction 4. chromosome loss and duplication 2. Mitotic recombination 5. gene conversion 3. deletion 6. point mutation

Question 28

genetic characteristics of oncogenes

Answer 28

Dominant mutations, gain of function, * in somatic cells -- NOT inherited (fatal in utero) less tissue preference.

Question 29

genetic characteristics of tumor suppressor genes

Answer 29

Recessive mutations (BOTH alleles must be affected), loss of function, in germ cell OR somatic cells ---> CAN be inherited *strong tissue preference

Question 30

why not more cancer w/ all cell divisions over lifetime?

Answer 30

1. need 2+ genetic events for cancer (1 mut. is not enough) | 2. usually* arise from 1 cell w/ multiple mutations (clonal in origin)

Question 31

Multi-Hit model of cancer induction

Answer 31

ALL cells in a tumor should have at least some COMMON genetic alterations. -- evidence: 1. cells from female tumors all have same X-chrom. inactivated; 2. cancer increases w/ age; 3. hard to induce cancer in animals w/ single oncogene; 3. successive muts in pathways

Question 32

Rb regulates which checkpoint type?

Answer 32

Rb: | regulates "Regulatory Point" (checkpoint)

Question 33

p53 regulates which checkpoint type?

Answer 33

p53: regulates DNA Damage checkpoints (aka: "guardian of the genome")

Question 34

dominant negative mutation

Answer 34

a genetic mutation in a single allele which inhibits the function of the other (wild type) allele - -> acts as dominant mutation. ie: Li-Fraumeni syndrome (affects p53 function)

Question 35

meiosis

Answer 35

1 round of DNA synthesis (replication), 2 successive rounds of cell division (w/ chromosomal segregation)

Question 36

major gametogenesis trigger

Answer 36

RA (retinoic acid), binds to nuclear receptors. responsible for regulating the timing of cells entering mitosis

Question 37

Splitting cell organelles in mitosis

Answer 37

* Key: want to split evenly, helped by cytoskeleton. - Mitochondria: double number, (so ubiquitous that this is enough) - All others (Golgi, ER): fragment into small pieces then regrow (Increases chance to split evenly btwn new cells)

Question 38

Cdk (cyclin dependent kinases)

Answer 38

Category of enzymes, for cell cycle regulation. Activated by binding cyclins, Active: phosphorylates cell cycle proteins

Question 39

G1 cyclins

Answer 39

w/ Cdk --> regulate activity of G1S cyclins; - activated by mitogens *D cyclin*

Question 40

G1S cyclins

Answer 40

In late G1, bind to Cdks to help pass restriction point; (Promote commitment into cell cycle) *E cyclin*

Question 41

S cyclins

Answer 41

Right after restriction point, Bind to Cdks to stimulate chromosome duplication. (Control early Mitotic events) *A cyclins*

Question 42

M cyclins

Answer 42

Bind to Cdks, --> stimulate entry into mitosis (M phase) *B cyclins*