Actin

[G1SG2]

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Cytochalasins interrupt actin polymerization by binding to the growing end of actin filaments. These drugs would most directly affect which of the following processes?

I. Cell crawling movements
II. Muscle contraction
III. Mitotic spindle formation

A. I only
B. III Only
C. I and II only
D. I, II and III

The answer is A, but why not C? We need actin filaments in sarcomeres, so why wouldn't it affect muscle contraction?

 

[capn jazz]

Microfilaments in sarcomeres aren't growing. One end is fixed to the Z line and the other likely has a cap because their length is constant.

 

[G1SG2]

Microfilaments in sarcomeres aren't growing. One end is fixed to the Z line and the other likely has a cap because their length is constant.

I know, but I was thinking we would need new ones? Do the microfilaments ever get replaced?

 

[capn jazz]

Even if that were so, it wouldn't affect muscle contraction immediately. If you add cytochalasin, muscles can still contract. I don't see any reason to think sarcomeres are dissembled and reassembled. Seems like it would be a waste of time/energy for the cell.

 

[matth87]

Cytochalasins interrupt actin polymerization by binding to the growing end of actin filaments. These drugs would most directly affect which of the following processes?

I. Cell crawling movements
II. Muscle contraction
III. Mitotic spindle formation

A. I only
B. III Only
C. I and II only
D. I, II and III

The answer is A, but why not C? We need actin filaments in sarcomeres, so why wouldn't it affect muscle contraction?

It wouldn't inhibit muscle contraction because it only inhibits actin formation. If the actin is already formed in the muscle inhibiting the formation of already formed actin would do nothing, so therefor it wont affect muscle contraction. It would affect muscle growth though.

 

[matth87]

I know, but I was thinking we would need new ones? Do the microfilaments ever get replaced?

Yes they actually do get broken down for example after you work out. You then build new sarcomeres which make your muscle stronger. Even inhibiting this though would only prevent your muscles from building up. It wouldn't inhibit their ability to contract. You still would have alot more sarcomeres and myofibrils.

 

[G1SG2]

Got it, thanks guys!

 

[matth87]

keep them coming! haha, btw I remember working this problem yesterday