Leftover material

Question 1

Cytoskeleton

Answer 1

1. Mirofilaments: actin, support to the apical microvilli
2. Microtubules: tubulin, for direction flow or vesicles
3. Intermediate filaments: for structure

Question 2

Microfilaments: actin

Answer 2

1. G-actin:
   -ATPase
   -has an ATP binding cleft
2. F-actin:
   - (-) end: exposed binding cleft
   - (+) end: burried end

Question 3

G-actin polymerization into F-actin filaments

Answer 3

1. Nucleation (lag) phase: inefficient formation of 3 ATP
2. Elongation phase: actin subunits rapidly assemble onto each end of a filament
3. Steady state phase: G-actin monomers exchange with subunits at filament ends but there is no net chance in length

Question 4

Actin treadmilling

Answer 4

ATP actin subunits assemble 10X faster at the positive end of an actin filament

Question 5

Regulation of actin filaments growth

Answer 5

-CapZ blocks + ends
-tropomodulin blocks - ends
-form in nucleate actin assembly

Question 6

Arp2/3 complex nucleates branched filaments

Answer 6

-drives internalized endocytosed vesicles away from the PM

Question 7

Signal induces changes in the actin cytoskeleton via small GTPases

Answer 7

Contributions to cell movement

Question 8

Microtubules: tubulin GTPase dimers

Answer 8

1. Alpha
   -GTP is never hydrolyzed
   -negative end
2. beta
   -GDP exchangeable with GTP
   -positive end
   -where subunits are preferentially added

Question 9

Centrosome (MTOC)

Answer 9

Positive ends outwards

Question 10

Nucleation of microtubules via the gamma tubulin ring complex (y-TuRC)

Answer 10

-augmin mediated branching of microtubules

Question 11

Dynamic instability depends on the presence/absence of a GTP-B- tubulin cap

Answer 11

-catastrophe: rate of GTP hydrolysis is greater than rate of GTP tubulin addition
-rescue: GTP tubulin addition is faster than GTP hydrolysis

Question 12

Microtubules are bundles together by microtubules associated proteins (MAPs)

Question 13

Intermediate filaments

Answer 13

-N terminus and C terminus
-assembled from subunit dimers
- protofilament -> tetramer -> protofibril -> mature filament

Question 14

Microtubules and intermediate filaments can be cross linked via plectin and IFAPs

Answer 15

Microfilaments: tracks for myosins
Microtubules: tracks for kinesins and Dyneins

Question 16

Myosin (on microfilaments)

Answer 16

-head, neck (2 light chains) ,tail (2 heavy chains)
-head has actin binding site and ATPase binding site separate
-walk toward the + end of actin filament
-ATP driven

1. ATP binding causes conformational change = head released from filament
2. Head hydrolyzes ATP to ADP + P = cocked state (stores the energy)
3. Head binds to actin filament
4. Binding to actin causes myosin to release P = power stroke
5. Head remains tightly bound to filament until ADP is released, fresh ATP bound, head released

Question 17

Ca sensitive protein tarpon in prevents binding of myosin to actin in the relaxed muscle

Answer 17

Ca = contraction

Question 18

Kinesins and Dyneins (on microtubules)

Answer 18

1. Kinesins: + end directed
2. Dyneins: - end directed

Question 19

Kinesins uses ATP to walk down a microtubule

Answer 19

1. Leading head with no nucleotide bounds is tightly associated with the microtubule
2. Leading head binds ATP
3. Linker region swings forward = new leading head
4. New leading head bind weakly
5. New leading head releases ADP and binds tightly
6. New trailing head hydrolyzes ATP to ADP + P
7. P release = weak binding

Question 20

Dyneins

Answer 20

-Dynein power stroke
-pre stroke: ADP + P
-post stroke: no nucleotide
-dynactin complex functions with dynein to transport cargo

Question 21

Cell cycle

Answer 21

G1: cell growth
S: DNA synthesis
G2: gap phase, preparing for mitosis
Mitosis:
1. Prophase
- replicated chromosomes condense
-mitotic spindle assembles between the 2 centrosomes (have replicated and moved apart)
2. Prometaphase:
-abrupt breakdown of nuclear envelope
-chromosomes attach to the mitotic spindle via their kinetechores
3. Metaphase: chromosomes align at the equator of the spindle
4. Anaphase: sister chromatids separate
5.telophase: chromosomes decondensate and nuclear envelope reforms
6. Cytokinesis: contractile ring pinshes off the cells in two

Question 22

Mitotic spindle

Answer 22

1. Astral microtubule: project toward the cortex
2. Kinetechore mts: connected to chromosomes
3. Inter polar: project toward the cell center with their distal + ends overlapping

Question 23

Cyclin dependent kinases (CDK)

Answer 23

-Cyclins activate the kinase domain
-G1/S cyclin, S cyclin, M cyclin
-3 important regulators of CDKs:
1. CAK: phosphorylates CDKs; activating kinase
2. Wee1: phosphorylates CDKs: inhibitory kinase
3. CDC25: phosphatase= removes inhibitory phosphate

Question 24

Cancer: abnormal Karyotypes

Answer 24

-Kataegis: antibody diversity
-chromothripsis: entire chromosome parts are shattered and stitched

Question 25

4 stages of carcinogenesis/ oncogenesis

Answer 25

1. Initiation 2. Cancer progression 3. Evasion of cancer cell elimination 4. Tumor growth and dispersal

Question 26

Energy production in cancer cells

Answer 26

Glucose -> pyruvate -> lactate

Question 27

Direct acting carcinogen: p-450

Question 28

Proto-oncogene receptors

Answer 28

HER2 and EGF receptor: constitutively active kinase -RTK pathway components are frequently mutated in cancer -in most tumors, p53 is inactivated (tumor suppressor)