Comprehension L16-L17

Question 1

Individual actin monomers move down the length of the microfilament (actin) from the plus end to the minus end in a process known as

Answer 1

Treadmilling

Question 2

Stimulatory/excitatory neurotransmitters released from the terminal knobs of a presynaptic cell will have which effect?

Answer 2

increased sodium influx into the postsynaptic cell

Question 3

What does Myosin Type 2 do?

Answer 3

Roles in muscle contraction, splitting cell during cell division, and cell motility

Question 4

How is Myosin 2 oriented?

Answer 4

Tails point towards the centre and heads point outside

Question 5

What are 2 characteristics of the Myosin filament?

Answer 5

Bipolar: Reversal of direction at the filament’s centre
Thick: Component of myosin

Question 6

In order of largest to smallest, what are the levels of muscles?

Answer 6

1. Muscle fibre, composed of hundreds of…
2. Myofibrils, composed of repeating contractile units called…
3. Sarcomeres, contractile unit with a characteristic banding pattern

Question 7

What is the Z line?

Answer 7

contains proteins important for sarcomere structure stability

Question 8

What is the M line?

Answer 8

Dark staining in the centre of the sarcomere, contains anchoring proteins.

Question 9

What do I bands contain?

Answer 9

Only thin filaments

Question 10

What is the H zone?

Answer 10

Contains only thick filament

Question 11

What is the A band?

Answer 11

Dark staining overlap of thick and thin, also includes the H zone

Question 12

Each thick filament is surrounded by what?

Answer 12

6 thin filaments

Question 13

How far can a single myosin move an actin filament in a power stroke?

Answer 13

10nm

Question 14

Describe the 5 steps of actin-myosin contraction

Answer 14

1. ATP binds to myosin head and myosin dissociates from actin
2. ATP hydrolysis, ADP and Pi remain bound
3. Energized myosin binds actin
4. Release of phosphate triggers conformational change: power stroke (actin moves to centre of sarcomere)
5. ADP is released

Question 15

Muscle fibres with a (__) are stimulated simultaneously by a single motor neuron

Answer 15

Motor unit

Question 16

What is the neuromuscular junction?

Answer 16

Point of contact between motor neuron and muscle fibre; site of transmission of the nerve impulse

Question 17

What are Transverse tubules?

Answer 17

Membrane folds that propagate an impulse to the interior of a muscle cell

Question 18

What is the Sarcoplasmic Reticulum

Answer 18

Special smooth ER in muscle cells; stores Ca2+ in lumen (pumped in from cytosol

Question 19

What does the arrival of an action potential at the SR do?

Answer 19

Opens Ca2+ channels, release Ca2+ into the cytoplasm

Question 20

Thin filaments contain actin and:

Answer 20

Tropomyosin - rod shaped
Troponin - globular

Question 21

What happens in the absence of Ca2+?

Answer 21

Troponin controls position of tropomyosin which blocks myosin-binding sites on actin

Question 22

What happens in the presence of Ca2+?

Answer 22

Ca2+ binds troponin which moves tropomyosin, exposing the myosin binding site on actin

Question 23

What blocks the myosin binding sites on actin thin filaments in a resting sarcomere?

Answer 23

Tropomyosin

Question 24

What blocks the myosin binding sites on actin thin filaments in a stimulated sarcomere?

Answer 24

Nothing

Question 25

What is the cell cortex and what is it's function?

Answer 25

Actin network on the inner face of the plasma membrane, dynamic remodelling, enable cells to crawl, enable phagocytosis, cellular constriction

Question 26

What do actin-binding proteins do?

Answer 26

regulate the assembly, disassembly, and rearrangements of actin networks

Question 27

What are the 7 steps of actin binding proteins?

Answer 27

1. Filament nucleating 2. Monomer sequestering 3. End blocking (Capping) 4. Monomer polymerizing 5. Depolymerizing 6. Cross linking 7. Filament severing

Question 28

In filament nucleation, what is the Arp2/3 complex?

Answer 28

Binds to the side of an existing filament Remains at the pointed end of new branch Similar structure to actin monomers

Question 29

In filament nucleation, what are formins?

Answer 29

Generate unbranched filaments Stay associated with the barbed end Promote rapid elongation of filaments

Question 30

What happens in monomer sequestering?

Answer 30

Bind to actin-ATP monomers to prevent them from being added to the elongating filament Able to modulate the available monomer pool in certain regions at certain times

Question 31

What happens in end blocking (capping)?

Answer 31

Regulate the length of actin filaments and bind at either end

Question 32

What happens in monomer polymerizing?

Answer 32

Binds to actin monomers to promote growth of actin filament Promotes replacement of ADP w ATP on the actin monomers

Question 33

What happens during depolymerization?

Answer 33

Bind to actin-ADP at the pointed end to promote depolymerization

Question 34

What happens with cross linking and bundling?

Answer 34

Multiple actin binding sites, allowing them to alter the 3D organization

Question 35

What is filament severing?

Answer 35

Break an existing filament in two

Question 36

What happens in membrane-binding?

Answer 36

Actin filaments linked to the plasma membrane Enabling the plasma membrane to protrude outward or inwards

Question 37

What does Arp2/3 do?

Answer 37

branched filament nucleating

Question 38

What is profilin?

Answer 38

Monomer polymerizing (ADP->ATP)

Question 39

What is Cofilin?

Answer 39

Depolymerizing

Question 40

A shift in the [ ] or activity of which types of actin binding proteins can cause a shift in the equilibrium between available actin monomers and filamentous actin?

Answer 40

- Monomer sequestering proteins - Depolymerizing proteins - Nucleating proteins

Question 41

What is the lamellipodium?

Answer 41

The leading edge of a moving cell that extends over the surface, broad and flat

Question 42

What promotes polymerization?

Answer 42

profilin

Question 43

What are the steps (1-4) of dynamic actin network at the site of lamellipodium formation?

Answer 43

1. Stimulus received at cell surface 2. Arp2/3 complex at site of stimulation gets activated 3. Arp2/3 binds the side of an existing filament 4. ATP-actin monomers bind to the Arp2/3 complex, forming a new actin branch

Question 44

What are the steps (5-6) of dynamic actin network at the site of lamellipodium formation?

Answer 44

5. Additional Arp2/3 complexes can bind to the sites of new filaments. Older filaments are capped at barbed end so they remain short and stable 6. Newer filaments continue to grow at the barbed end, pushing the membrane of the lamellipodium outward

Question 45

What are traction forces?

Answer 45

When the cell grips the surface at adhesion points called focal adhesions

Question 46

What are focal adhesions?

Answer 46

Structures in the cell membrane where integral proteins connect to actin

Question 47

What are Integrin proteins?

Answer 47

Transmembrane proteins that mediate the interaction between actin and extracellular components

Question 48

What are Contractile forces?

Answer 48

Pull the bulk of the cell forward Myosin found near the rear of the lamellipodium