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Home Q & A Board Biology-Related Homework Help Biochemistry
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wrote...
13 years ago
which of the following are true about microfilaments?

1. polymerization of actin generally occurs more slowly at the (-) end of the actin polymer.
2. microfilaments are larger in diameter than intermediate filaments.
3. microfilaments are motor proteins
4. polymerizing microfilaments contain more bound ATP whereas older microfilaments contain more bound ADP.
5. the monomeric form of actin is called G-actin.

I thought that 1,3, and 5 were the only ones correct; However, this is wrong.  Then I thought that all except 2 were right, but it is also wrong.  But could the correct answer be 1,4,and 5.  Thank you very much for your help! Slight Smile
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wrote...
#1
Educator
13 years ago
which of the following are true about microfilaments?

1. polymerization of actin generally occurs more slowly at the (-) end of the actin polymer.
2. microfilaments are larger in diameter than intermediate filaments.
3. microfilaments are motor proteins
4. polymerizing microfilaments contain more bound ATP whereas older microfilaments contain more bound ADP.
5. the monomeric form of actin is called G-actin.

Slight Smile
nickname Author
wrote...
#2
13 years ago
Hi. Thank you for replying, but I cheked your answer and it is incorrect.

The hint they give me is:
consider that the action of motr proteins is responsible for the movement of organelles within a cell.  consider that actin contains a cleft where ATP may bind. after actin polymerizes, the bound ATP hydrolyses into ADP and Pi.  So I was thinking that maybe the correct answers are 2,3,4, and 5. what do u think?  thank you so much for your help! Slight Smile
wrote...
#3
Educator
13 years ago
I always thought that actin exists as a globular monomer called G-actin. Microfilaments are formed by the head-to-tail polymerization of actin monomers (also known as globular or G-actin).
wrote...
#4
13 years ago
i agree with bio_man answer about G-actin

they are not motor proteins.. the motor proteins for actin filaments are myosin.
regarding the 4th answer, polymerization of actin filaments requires ATP, and in order for it to occur ATP should be hydrolyzed to ADP, so i guess we can say that this answer is correct since in polymerizing microfilaments ATP is just starting to hydrolyze, where as in older microfilaments ATP has already been transformed into ADP, but im not sure that it is correct to assume that ATP wouldn't be hydrolyzed instantly when it binds to its receptor.
wrote...
#5
13 years ago
and i checked my book.. they say that " this reaction ( talking about polymerization ) occurs mainly at one extremity which is referred to as plus end ". So they didn't say entirely, so i guess polymerization does happen to a lesser extent on the (-) end, so this could be also right, but i doubt it.
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