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BMEG 245 > Ch 17 > Flashcards

Ch 17 Flashcards

1
Q

types of protein filaments

A
  1. intermediate filaments (structure)
  2. microtubules (structure + transportation of cells i.e where motor proteins walk on)
  3. actin filaments (pull chromatids apart in cell division)
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2
Q

function of desmosome

A

connects two cells via adhesion

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3
Q

Structure of intermediate filament proteins

A

alpha helical
- exists as monomer, dimer, or staggered antiparallel tetramers
combines to create symmetric structure (max array of 8 tetramers)

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4
Q

4 major classes of intermediate filaments

A
  1. keratin (epithelial cells)
  2. vimentin (connective tissue, muscle, and glial cells)
  3. neurofilaments
  4. nuclear lamins

(1 - 3) are cytoplasmic

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5
Q

function of intermediate filaments

A

support and strengthen nuclear envolpe (or any plasma membrane)

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6
Q

function of plectin

A

links intermediate filaments to other networks (i.e other filaments such as actin filaments)

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7
Q

function of protein complexes in respect to filaments

A

bridge nucleus + cytoplasm on nuclear membrane

ex. KASH-domain (cytosol)
ex. SUN-domain (Nucleus)

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8
Q

what do KASH-domain proteins bind to?

A

microtubules, plectin, actin (microtubules bind via motor proteins)

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9
Q

what do SUN-domain proteins bind to?

A

nuclear lamina + chromatin

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10
Q

structure of micro tubules

A

13 parallel protofilaments (forms hollow tube)

tubulin dimers add to the plus end more than minus end
beta –> plus end
alpha –> minus end

polymerizes from nucleation sites on centrosome

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11
Q

Key property of microtubules

A

dynamic instability
–> grows when there are more dimers
–> shrinks when there are less dimers
controlled via GTP hydrolysis

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12
Q

Purpose of microtubules capping protein

A

captures microtubule to make it stable (therefore it won’t break down)

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13
Q

function of microtubules

A

guide the transport of organelles, vesicles, and macromolecules
help position organelles

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14
Q

What is Mitotic arrest

A

cells stop dividing (also caused when tubules stop growing)
–> drugs cause this to treat cancer growth

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15
Q

types of motor proteins

A

cytoplasmic denein –> moves towards minus end of microtubules (back towards nucleus)

kinesin –> moves in plus end
(away from nucleus)

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16
Q

How do motor proteins walk?

A
  1. one head gains ATP
  2. changes conformation (P is released)
  3. that head pulls “forward”
  4. binds to microtuble and other head gains ATP to repeat cycle
17
Q

How are microtubules formed in a cilium / flagellum

A

9 + 2 array
9 –> microtubules on outer layer
2 –> microtubules in center

18
Q

Relationship between dyneins + flagellum

A

dyneins cause flagellum to bend

19
Q

Compare and contrast microtubules and actin filaments

A

Differences:
- Actin filaments are shorter than microtubules
- total length of actin filaments is longer than microtubules
- Actin supports movement + structure (ex. filpodia, microvili, contractile ring in cell division)
- Microtubules support structure

Similarities:
- both grow faster at their plus end (dynamic instability for microtubules, tread milling for actin)
- both composed of protein units
- both involved in motor protein movement (dyneins and kinesines move along microtubules, myosins move along actin)

20
Q

How do actin filaments grow based on actin monomer concentration?

A

Concentration is high –> grow rapidly at both ends

concentration is middle –> tread milling (actin goes out at minus end + actin goes in at plus end at same rate)

21
Q

What are the types of actin-binding proteins and their functions?

A
  1. nucleating proteins:
    binds to minus end and stop degradation
  2. monomer-sequestering protein
    prevents polymerization
  3. severing protein
    hydrolyzes long actin filaments
  4. bundling protein
    used in creation of filopodia
  5. cross-linking protein
    - links actin in cell cortex to strengthen membrane

6.capping protein
- stops growth

  1. side-binding protein (tropomyosin)
    - forms coils to block myosin and other proteins from binding to actin
22
Q

How is actin used in cell crawling?

A
  1. actin polymerization protrudes lamellipodium (reach)
  2. attaches to surface by focal contacts that contain integrins (grab)
  3. myosin motor proteins slide along actin filament (pull)
23
Q

Compare and contrast myosin 1 and myosin 2

A

Myosin 1
- moves towards plus end (to plasma membrane)
- associated with movement of vessicles

Myosin 2
- associated with movements of muscles (slides two actin filaments together to contract)
- often forms bipolar (actin filament binding at both ends) filaments

24
Q

Explain the structural differences between lamellipodia and filopodia and their associations with the two actin filament nucleating proteins: formin and the actin-related protein (ARP) complex

A

Lamellipodia (sheet feet) –> contains more ARP complex to form mesh-like structures

filopodia (spike feet) –>
contains more formin to creaate long structures

25
Q

What do the Rho-family GTPases do?

A

promotes formation of rapid assembly of long unbranched actin filaments (Rho),
lamellipodia (Rac),
and filopodia (Cdc42)

26
Q

Describe the structure and movement of a sacromere

A

Structure:
- Z disc: binds sacromeres together
- actin filaments: attaches to Z disc at plus end + myosin filament at minus end
- myosin filament: at centre of sarcomere

Function:
contraction: mysosin pulls on actin filaments –> shortens sarcomere
relaxation: myosin releases actin filaments

27
Q

Describe the ATP-dependent cycle of myosin 2 (how it walks across actin filaments)

A
  1. Attached
    - myosin and actin are binded together (rigor configuration)
  2. Released
    - ATP binds to head of myosin that causes conformation changes –> myosin lets go of actin b/c reduced affinity
  3. Cocked
    - head of myosin tightly clamps around ATP molecule
    - ATP molecule hydrolyzes into ADP and P (but still binded to myosin)
    - myosin head moves 0.5 mm in direction of minus end of actin filament
  4. Rebending + Power stroke
    - ADP + P are released when myosin head weakly binds to new actin filament site –> myosin can now bind tightly to actin filament
28
Q

Describe the mechanics of skeletal muscle contraction

A
  1. triggered by release of Ca2+
    - Ca2+ release channel on Sarcoplasmic Reticulum is connected to voltage gated Ca 2+ channel
    - When T-Tubule membrane is activated by an action potential: voltage gated Ca2+ channels open and also causes the Ca2+ release channel to open
    - both lumen of T-tuble and sarcoplasmic reticulum release ca2+ into cytosol
    –> creates myofibril contraction
  2. controlled by tropomyosin + troponin complex

tropomyosin: string that blocks myosin 2 from binding (prevents premature contraction)

troponin: protein complex with Ca2+ sensnsitive protein

both proteins ensure that contraction occurs only when action potential is released

BMEG 245 (14 decks)

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