Week 13: (B) Coupling and Skeletal Muscle Contraction

Question 1

What are the 3 proteins of the thin filament?

Answer 1

Troponin, Actin, Tropomysosin

Question 2

what are the 3 types of Troponin?

Answer 2

Troponin T, I & C

Question 3

what does Troponin T do?

Answer 3

binds to trypomyosin-

Question 4

What does Troponin I do?

Answer 4

bind to actin inhibit contraction

Question 5

What does Troponin C do?

Answer 5

binds to Ca+

Question 6

Structure of Actin?

Answer 6

double stranded alpha-helical

Question 7

Does actin have a binding site?

Answer 7

BS for attachment with myosin cross bridge

Question 8

What happens to troponin when NOT bound to Ca+?

Answer 8

stabilises tropomyosin in its blocking position over the actin cross bridge BS.

Question 9

Tropomyosin structure?

Answer 9

2 stranded helixes wrap around each other to form a ribbon, this wraps around the actin and the troponin attached to this

Question 10

What chains are present in thick filaments?

Answer 10

2 heavy chains, 2 regulatory light chains, 2 chains alkali chains.

Question 11

What does the Alkali light chain do on the myosin head region?

Answer 11

stabilises head region

Question 12

What does the regulatory light chain do on the myosin head?

Answer 12

Regulates ATPase activity of myosin

Question 13

What regulates ATPase activity of myosin?

Answer 13

RLC which is in turn regulated by phosphorylation by kinase

Question 14

what does the heavy chain do on the head region of myosin?

Answer 14

binding site for actin

binding and hydrolysing ATP

Question 15

what can the heavy head region also be called?

Answer 15

S1

Question 16

What do the heads of myosin form?

Answer 16

cross-bridge

Question 17

what type of myosin attached to actin?

Answer 17

Myosin-ii

Question 18

what is step 1 of a muscle contraction?

Answer 18

myosin-ii heads bind to actin, cross-bridge becomes distorted, myosin heads detach from myosin

Question 19

What happens to ATP for myosin heads to move away?

Answer 19

Hydrolysis of ATP

Question 20

How is a muscle contraction triggered?

Answer 20

increase Ca2+ concentration

Question 21

What does increased Ca2+ concentration do?

Answer 21

removes inhibition of cross bridge cycling

Question 22

How does Ca2+ modulate contractions?

Answer 22

regulatory proteins act together to inhibit myosin and actin interactions

Question 23

What does Ca+ bind to to stimulate a contraction?

Answer 23

Troponin C. release inhibition of Troponin I (bound to actin to block cross-bridge)

Question 24

Where does ATP bind on Myosin?

Answer 24

Heavy chain

Question 25

What happens when ATP is bound to Myosin? (pt 1)

Answer 25

Reduce affinity for actin, detachment

Question 26

How is a muscle cell relaxed?

Answer 26

ATP bound to Myosin

Question 27

What happens when hydrolysis of ATP on myosin occurs? (pt 2)

Answer 27

Remains on the myosin, myosin swings back. cocked state lines up with a new actin monomer

Question 28

When is the muscle relaxed?

Answer 28

ATP is bound, Myosin head swings back

Question 29

when will the cross-bridge form?

Answer 29

If intracellular Ca2+ concentrations are high enough

Question 30

What happens to ADP + Pi when cross-bridge is formed?

Answer 30

inorganic phosphate released, triggers power stroke

Question 31

What happens in the power stroke?

Answer 31

Myosin head confo change, move ~45 degrees about the hinge, pulls actin towards tail of myosin

Question 32

what happens after the power stroke?

Answer 32

ADP is released, myosin complex left in a rigid state.

Question 33

How can the myosin-actin complex be relaxed?

Answer 33

ATP binding to heavy chain on head of myosin= relaxed

Question 34

Do the thin of thick filaments move when contracting?

Answer 34

Thin slide over thick

Question 35

Does the sarcomere shorten?

Answer 35

YES as thin filaments move closer together

Question 36

Does the A band change width?

Answer 36

no, stays the same width

Question 37

does the I band width decrease?

Answer 37

Yes, don't overlap thick so shorten

Question 38

does the H zone decrease?

Answer 38

Yes, similarly to the M line

Question 39

Does the Z line decrease?

Answer 39

Yes, distance between decrease

Question 40

What happens in riggor mortis?

Answer 40

Ca2+ rise (starts around 3-4hrs after death, complete in 12hrs) Allow actin to bind to myosin No ATP produced from the death body so stuck in rigid state

Question 41

what happens when Ca2+ binds to Troponin on tropomyosin?

Answer 41

Binds to Troponin C to remove the blocking Troponin I by shifting it to expose the Myosin binding site. Also TnT moved away from binding site into a groove