Question

1. Which of the following statements is incorrect:

1. A cross section of an “I” band would not contain myosin
2. The zone of Overlap gets bigger when “Z” lines move closer together
3. The Myosin head bonds to the active site of a G actin monomer
4. The “A” band shortens when a sarcomere contracts

2. Depolarization down a T Tubule Results in the activation of:

1. SERCA
2. RyR
3. CSQ
4. DHPR

3. How many “I” bands are present in one sarcomere:

1. 0
2. 1
3. 2
4. 3
5. 4

4. Which region of a sarcomere gets wider during contraction:

1. H zone
2. Zone of overlap
3. A band
4. I band

5. What is the function of the smooth endoplasmic reticulum calcium ATPase (SERCA):

1. Pump calcium out of a t tubule
2. Pump calcium into a t tubule
3. Pump calcium back into the SR
4. Pump calcium out of the SR

Answer 1

1.The incorrect statement is option d - A band shortens when a sarcomere contracts.

Expalnation : During muscle contraction A band remains unchanged.I band shortens.

** Cross section of I band contains only actin. But cross section of A band contain both actin and myosin. Overlapping region is included in A band.

**Myosin head binds to the active site of a G actin monomer is correct statement.

Actin is made up of G actin monomer. Actin contains active site for myosin which is masked by troponin.

**Zone of overlap gets bigger when Z lines move close together is correct statement. The part of myofibril between two successive z lines is called sarcomere - the functional unit of muscle contraction.

2.Correct answer is option d - DHPR

Expalnation : DHPR - Dihydropyridine receptors sense the action potential on T tubule and relays it to the Ryanodian receptors(RyR) on sarcoplasmic reticulum membrane. Release of calcium ions from sarcoplasmic reticulum takes place and these calcium ions trigger the process of muscle contraction.

Contraction is shutoff by reuptake of calcium back into sarcoplasmic reticulum. It is mediated through SERCA receptors

CSQ - Calsequestrin - - > It acts as a calcium sensor for ryanodian receptors.It gives information about calcium load to ryanodian receptors.

3.Correct answer is option C - 1

Expalnation : only one I band in one sarcomere.

In the above diagram, we can see half of I band on both sides of sarcomere - - >both add together to form one I band in sarcomere.

4. Correct answer is option b - Zone of overlap

Expalnation :

During contraction of muscles, actin and mysosin would get overlapped and shortens the length of myofibril.

**H zone either decreases or finally disappears during severe muscle contraction.

**A band remains unchanged

**I band decreases since actin filaments from opposite side overlapp.

5 Correct answer is option C- pump calcium back into the sarcoplasmic reticulum.

Explanation : SERCA mediates the calcium reuptake to sarcoplasmic reticulum. Refer question 2 explanation.