Cell Biology: Cytoskeleton

Front 1

Which cytoskeleton subunit is the strongest?

Back 1

Intermediate Filaments

Front 2

Which cytoskeleton subunit is the thickest?

Back 2

Microtubules (25 nm)

Front 3

Which cytoskeleton is composed of alpha and beta subunits?

Back 3

Microtubules

Front 4

What are intermediate filaments made of?

Back 4

Keratin filaments and lamins

Front 5

What are the types of Actin Filaments & Microfilaments and their responsibilities?

Back 5

alpha = contractile structures
beta = movement
gamma = stress fibers (associated with integrin receptors)

Front 6

G actin? F Actin?

Back 6

-G actin has ATP associated to it, can add to growing F-actin
F-actin = composed of G actin, double helix

Front 7

Describe actin filament structure.

Back 7

-s1 myosin head - decorates actin filaments
-polarity (+ and - ends)

Front 8

Test tube experiment of isolated actin

Back 8

-observed polymerization of actin filaments
-nucleation --> elongation --> steady state
-sigmoidal shaped
In the steady state:
-The length of the actin filament stays the same
-There is a preferential (net) addition of G-actin to the + end
-There is a preferential (net) loss of G-actin to the – end
-Treadmilling occurs

Front 9

What is the CRITICAL CONCENTRATION?

Back 9

-applies to F actin and myosin
-it is the G actin concentration at which there is no net change in filament length
-Cc+ = 0.12 uM
-Cc- = 0.6 uM

Front 10

What is "treadmilling" ?

Back 10

-occurs when one end of a filament grows in length while the other end shrinks
- b/c of constant removal of the protein subunits from filaments at one end of the filament while protein subunits are constantly added at the other end

Front 11

Poisons of actin and microfilaments?

Back 11

- cytochalasin D = fungus, inhibits polymerization at the + end

- phalloidin = "angel of death", binds to F-actin with high affinity --> promotes polymerization; cure = eat raw meat; flourescent label

Front 12

Actin binding proteins of actin and microfilaments?

Back 12

- thymosin beta-4 = protein that binds to G actin; increases the G-actin pool in cells

- profilin = promotes F actin assembly by promoting the exchange of ADP to ATP; protein

- cofilin = severs F-actin

Front 13

Severing/Capping Proteins of actin and microfilaments?

Back 13

- Cap Z = caps/stabilizes the + end
- tropomodulin = caps/stabilizes the - end
- cofilin - severing protein
- gelsolin - severing protein
- formin - dimer; nucleates G actin to form F actin; caps the + end

Front 14

What are optical traps of actin/microfilaments and what do you need?

Back 14

- method of studying F-actin; need actin, myosin, and infrared laser

Front 15

What is Listeria monocytogaves and how does it work? What is the function of the protein, Act A?

Back 15

- bacteria
- food poisoning
- can cross to the fetus if pregnant
- comes in via phagocytosis, doesn't go through lysosomes
- can mobilize G actin into F-actin --> allows this to enter another cell = BAD!


Act A is found on the bacterium cell surface and activates the Arp2/3 complex to nucleate new filament assembly from preexisting filaments.

Front 16

Diaphenous gene

Back 16

Large family in costa rica - 50% deaf
- actin assembly defect in hair cells

Front 17

Hair cells

Back 17

Transducer = sound waves to Vm (info)

Front 18

When hair cells are bent by soundwaves...

Back 18

the "doors" open --> increase in [K+] influx

Front 19

When hair cells are NOT bent by soundwaves...

Back 19

the "doors" close --> no K+ influx

Front 20

What are the FIVE types of genes that encode for intermediate filaments?

Back 20

I+II = keratins
III - skip it
IV - neurofilaments - structure (axons)
V - lamins - structure; connects DNA with nuclear envelope, triggers nuclear dissolution (mitosis)

Front 21

What is/are the role(s) of lamins?

Back 21

- connect DNA with nuclear envelope
- triggers nuclear dissolution (mitosis)
-once phosphorylated by MPF --> it breaks down and cannot hold chromosomes together --> chromosome separate

Front 22

Mesenchymll cells

Back 22

-replace cells --> reconstitute through tissue repairment; paracrine factory --> repair damaged tissue

Front 23

New Neural Company

Back 23

- nerve cell regeneration
- take smart mouse --ablation --> dumb mouse now --> take bone marrow cells --> neurons --> take mesenchymal stem cells --> smart mouse now

Front 24

IF3

Back 24

- human specific anti-IF3 Ab
- neurons (mesenchymal cells ) were HUMAN, NOT mouse

Front 25

Epidemolysis Bullosa

Back 25

- defect in keratins
- genetic disease
- skin shears off, but the basal lamina is fine
- problem lies in above basal lamina

Front 26

What does colchicine do?

Back 26

Inhibits microtubules from working

Front 27

When [cAMP] is decreased in Fish pigment cells in the dark, what happens? and vice versa?

Back 27

you get fish pigment cells in the light

Front 28

What happens when you take fish pigments in the light, increase [cAMP] and add colchicine? Why?

Back 28

Nothing, because the vesicles are already using the microtubules

Front 29

What happens when you cut off a piece of starfish (?) ?

Back 29

The microtubules will spontaneously organize.

Front 30

What is MTOC?

Back 30

Microtubules Organizing Centers

- the site of microtubule nucleation
- organization of eukaryotic flagella and cilia
- organization of the mitotic and meiotic spindle apparatus separating the chromosomes during cell division

Front 31

What are the two most important types of MTOCs?

Back 31

- basal bodies associated with cilia and certain intercellular junctions in epithelial cells
- the centrosome associated with spindle formation

Front 32

What happened in the clamydromonas experiment?

Back 32

Microtubules were taken and cut off from the cell. The microtubules were R123-labeled and allowed to grow with another cell. When the microtubules of the other cell grew, the alpha, beta tubulin was added to the ends of the microtubules. Shows that the information (?) was being shared

Front 33

What are MAPs?

Back 33

Microtubule-associated proteins.

-variety of proteins that typically co-purify with tubulin
- have a variety of functions

Front 34

What does Tau have a major effect on?

Back 34

Axons (they shorten greatly)

Front 35

What does MAP-2 have a major effect on?

Back 35

Dendrites

Front 36

What does Kinesin 13 do?

Back 36

Binds to the positive end, causes depolarization of microtubules

Front 37

What does Sthamin do?

Back 37

It's an oncoprotein, binds to the + end, depolymerizes microtubules

Front 38

Vesicles move in what direction with kinesin?

Back 38

Anterograde

Front 39

Vesicles move in what direction with dynein?

Back 39

Retrograde

Front 40

Kinesin 1,2 is responsible for what?

Back 40

vesicle movement

Front 41

Kinesin 5 is responsible for what?

Back 41

microtubules sliding against microtubule

Front 42

What are the inhibitors of molecular motors?

Back 42

-Colchicine/nocodazole
-taxol/taxotere

Front 43

How does taxol work? How does taxotere work?

Back 43

Taxos polymerizes microtubules. Taxotere (a synthetic alternative) interferes with microtubules in dividing cells.

Treat breast/prostate/ovarian cancer

Front 44

Describe cilia.

Back 44

- have hair like processes that have microtubules
- move in a wave-like motion
- reduces drag

Front 45

Describe flagella.

Back 45

- have hair like processes that have microtubules
- move in an undulating motion
- uses dynein (NOT kinesin)

Front 46

What is nexin?

Back 46

- keeps microtubules in place
- prevents microtubules in the outer layer of axonemes from movement with respect to each other.

Otherwise vesicular transport proteins such as dynein would dissolve the whole structure.

Front 47

What happened in the telescoping experiment?

Back 47

Took isolated cilia, removed outer membrane, added ATP --> get intact cilium with bending

Took isolated cilia, removed outer membrane, removed nexin, added ATP --> get "telescoping" or sliding

shows that nexin keeps microtubules in place

Front 48

What factors affect the polymerization/depolymerization actin filaments?

Back 48

ATP.

When ATP is bound to G-actin, it can polymerize to form F-actin.

Front 49

What happens when the concentration of free units is OVER that of the critical concentration?

Back 49

there would be a subunit addition at both ends of the microtubules

Front 50

What happens when the concentration of free units is BELOW that of the critical concentration?

Back 50

results in subunit removal at both ends

Front 51

Define the Arp2/3 complex and describe its contribution to cell migration and locomotion.

Back 51

- 7-subunit protein
- stimulates nucleation of reaction of actin filaments
- helps with polymerization of actin
- activated by increase in [RAC] at leading edge of cell (part of cell moving forward)

Front 52

What are cdc42, Rac, and Rho, and how to they work together during cell migration?

Back 52

cdc42, Rac & Rho = small GTP binding proteins; regulate cell migration