Ch 17

Question 1

types of protein filaments

Answer 1

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)

Question 2

function of desmosome

Answer 2

connects two cells via adhesion

Question 3

Structure of intermediate filament proteins

Answer 3

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

Question 4

4 major classes of intermediate filaments

Answer 4

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

(1 - 3) are cytoplasmic

Question 5

function of intermediate filaments

Answer 5

support and strengthen nuclear envolpe (or any plasma membrane)

Question 6

function of plectin

Answer 6

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

Question 7

function of protein complexes in respect to filaments

Answer 7

bridge nucleus + cytoplasm on nuclear membrane

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

Question 8

what do KASH-domain proteins bind to?

Answer 8

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

Question 9

what do SUN-domain proteins bind to?

Answer 9

nuclear lamina + chromatin

Question 10

structure of micro tubules

Answer 10

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

Question 11

Key property of microtubules

Answer 11

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

Question 12

Purpose of microtubules capping protein

Answer 12

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

Question 13

function of microtubules

Answer 13

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

Question 14

What is Mitotic arrest

Answer 14

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

Question 15

types of motor proteins

Answer 15

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

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

Question 16

How do motor proteins walk?

Answer 16

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

Question 17

How are microtubules formed in a cilium / flagellum

Answer 17

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

Question 18

Relationship between dyneins + flagellum

Answer 18

dyneins cause flagellum to bend

Question 19

Compare and contrast microtubules and actin filaments

Answer 19

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)

Question 20

How do actin filaments grow based on actin monomer concentration?

Answer 20

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)

Question 21

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

Answer 21

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

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

Question 22

How is actin used in cell crawling?

Answer 22

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)

Question 23

Compare and contrast myosin 1 and myosin 2

Answer 23

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

Question 24

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

Answer 24

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

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

Question 25

What do the Rho-family GTPases do?

Answer 25

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

Question 26

Describe the structure and movement of a sacromere

Answer 26

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

Question 27

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

Answer 27

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

Question 28

Describe the mechanics of skeletal muscle contraction

Answer 28

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