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MCB - Dr. Zaidi > White Cyto 2 > Flashcards

White Cyto 2 Flashcards

1
Q

Actin accessory proteins have three types of affects. What are they?

A
  1. Affect actin subunits.
  2. Affect actin filaments.
  3. Affects filament bundling, cross linking, and attachment to membranes.
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2
Q

The four proteins that affect actin SUBUNITS are?

What are their functions?

A
  1. ARP Complex: nucleates assembly of weblike, highly branched chains. Associated with (-) end.
  2. Formin: nucleates assembly of long, UNBRANCHED chains. Associated with (+) end.
  3. Thymosin: binds actin subunit/monomer, prevents assembly.
  4. Profilin: binds actin subunit/monomer, promotes assembly by speeding elongation.
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3
Q

The ARP complex consists of two Arp proteins, ___ and ___.

When the complex binds to an activation factor, inducing a conformational change, the complex mimics what end of actin?

This is a FAST process because it bypasses the rate-limiting step of actin growth, which is what?

A

Arp2 and Arp3.

(+) end.

rate-limiting step = filament nucleation.

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4
Q

The reason why Listeria can move around so fast in a cell utilizing actin filaments is because of this protein, which does what?

A

ActA.

ActA is another activating factor of the ARP Complex, allowing nucleation and growth of actin filaments.

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5
Q

What actin filament structure allows the most efficient functioning of the ARP complex?

A

ARP is most efficient when bound to the side of a preexisting actin filament, cross-linked at 70 degree angle.

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6
Q

The ARP Complex and Formins help regulate cell movement by forming these two types of cell projections…

A

Lamellipodia: flat, protrusive veils.

Microvilli/filopodia: long, spiky bundles.

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7
Q

The formin protein has a ____ structure. Each formin subunit binds ____, at this end, ___, of the actin filament.

A

dimeric.

each subunit binds one actin monomer, therefore the formin dimer captures two monomers.

(+) end, or growing end.

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8
Q

This protein keeps actin polymers available for actin polymerization. How does it do this?

The result of thymosin binding with actin monomer is what?

A

Thymosin.

By keeping actin monomer SOLUBLE, thymosin allows the monomer to be readily available for generating filaments.

Thymosin bound to actin monomer results in no growth of actin filament.

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9
Q

This protein binds to actin monomers, recruiting them to the actin filament for polymerization.

The result of profilin binding to actin monomer results in what?

A

Profilin.

Profilin binding results in rapid growth of actin filament.

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10
Q

Name the five proteins that affect actin FILAMENTS.

Which ones stabilize the actin filament?

Which ones are involved in disassembly?

A
  1. Tropomodulin
  2. Tropomyosin
  3. Capping protein
  4. Cofilin
  5. Gelsolin

Stabilize: Tropomodulin, tropomyosin, capping protein.

Disassembly: Cofilin, Gelsolin.

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11
Q

What does Tropomodulin do?

A

Prevents assembly/disassembly at (-) end. This stabilizes the actin filament (muscles).

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12
Q

What does Tropomyosin do?

A

Stabilizes filament by preventing binding with other proteins.

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13
Q

What does Capping protein do?

What protein serves this same function, but at the other end of capping protein?

A

Prevents assembly/disassembly at (+) end by reducing the rate of polymerization and depolymerization.

Tropomodulin also prevents assembly/disassembly, but at (-) end.

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14
Q

What does Cofilin, also known as ____, do?

What protein could be considered to have the opposite function of cofilin?

A

Cofilin is also called Actin Depolymerizing Factor.

Cofilin finds to ADP-actin filaments and disassembles filaments by forcing the filament to twist tightly, weakening contact points between actin subunits.

Tropomyosin stabilizes while cofilin disassembles.

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15
Q

What does Gelsolin do?

What end does Gelsolin bind to?

A

Gelsolin severs actin filaments, making smaller filaments available for elongation or disassembly.

Gelsolin binds to (+) end.

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16
Q

What 5 proteins are involved with actin filament bundling, cross-linking, and membrane attachment?

A
  1. alpha-actinin
  2. Fimbrin
  3. Filamin
  4. Spectrin
  5. ERM Family
17
Q

Actin filaments come together in two types of organization. What are they and what proteins are associated with each structure?

A

Bundle: parallel, cross-linked array of either alpha-actinin or fimbrin.

Web-like organization (also called gel-like): creates a looser meshwork and the actin filaments are held together by filamin.

18
Q

Compare/contrast alpha-actinin, fimbrin, filamin.

A

alpha-actinin: cross-links actin filaments into LOOSE bundles. allows myosin-II entry.

fimbrin: cross-links actin filaments into TIGHT bundles. does NOT allow myosin-II entry.
* you usually find alpha-actinin OR fimbrin, mostly based on function.
filamin: loose, highly viscous, gel-like networks. Cells require actin gel to extend membrane/crawl on solid surface.

19
Q

What two proteins attach the cytoskeleton to the membrane? Describe their function

A

Spectrin and ERM Family.

Spectrin: attaches actin to plasma membrane. RBC stability/durability. (Defective Spectrin = hemolytic anemia or Hereditary Spherocytosis (HS)).

ERM: mediates attachment of actin to plasma membrane. Two attachment points on ERM: actin filament and transmembrane protein.

20
Q

Accessory proteins that control assembly and position of cytoskeletal filaments fall into what three major groups?

A
  1. tubulin dimers
  2. microtubules
  3. filament cross linking
21
Q

Describe the three proteins that are associated with tubulin dimers.

A

Stathmin: binds subunits, prevents assembly.

TIPS: plus-end tracking proteins that stay on growing plus end. can attach to membranes.

gamma-TuRC: responsible for nucleation of MT growth.
remains associated with minus end.

22
Q

What location do microtubules nucleate from and what protein is attached to it? In animal cells, this is also known as what?

A

microtubule-organizing center (MTOC), and gamma-TuRCs are attached to MTOC, also known as the centrosome in animal cells.

23
Q

What end of microtubules, + or -, is attached to the centrosome?

A

minus ends attached to centrosome, via gamma-TuRCs. plus ends point outward away from centrosome.

24
Q

What 4 proteins are involved with regulation of stability of MT filaments?

A
  1. Katanin (“sword” severs MTs)
  2. MAPs
  3. XMAP215
  4. Kinesin 13
25
Q

What do MAPs do and where do they bind? Name a specific Xenopus MAP that does this.

A

MAPs stabilize MT against disassembly, stabilizing the free end and inhibiting catastrophe (switch from growth state to a shrinking state). MAPs bind alongside the microtubules.

XMAP215 = Xenopus MAP (same function as above).

26
Q

What does Kinesin-13 do?

A

Kinesin-13 binds to MT ends and prys protofilaments apart by lowering the activation energy that prevents a MT from coming apart.

K-13 helps switch from a growing to a shrinking state, aka catastrophe.

27
Q

What three proteins are involved in MT filament cross linking and what are their functions?

A

Plectin: cross-linking protein, links MTs to intermediate filaments.

MAP2: forms bundles of MTs that are widely spaced apart.

Tau: forms bundles of MTs that are closely packed.

28
Q

The two motor proteins, ____ and ____, use energy derived from ____ to move cargo along filament. Which motor protein moves towards the plus end, or away from the kinetichore?

A

Kinesin and Dynein.

ATP Hydrolysis.

Kinesin moves towards the plus end, away from the kinetichore/centrisome.

29
Q

Both motor proteins contain two regions.

This region, ____, attaches to the MT and hydrolyzes ATP for motion/energy.

This region, ____, attaches the cargo, also the C terminus.

A

motor domain (head).

tail.

30
Q

This motor protein is the largest of the known molecular motors and the fastest.

A

Dynein.

31
Q

Cytoskeleton is also used for cell behavior structures, such as cilia and flagella. What motor protein is responsible for the beating of these structures?

A

Dynein.

32
Q

Cell crawling is important in emryonic morphogenesis, immune surveillance, and cancers. Neutrophils detect bacterial ____ to move towards the bacteria.

A

peptides.

MCB - Dr. Zaidi (12 decks)

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