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Home Q & A Board Biology-Related Homework Help Cell Biology
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Shamrock Shamrock
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12 years ago
I know that the diameter of a microtubule is 25 nm, but my homework is to show the work calculating this.  I am at a total loss.  Could someone please show me how to calculate it?
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#1
Staff Member
12 years ago
Quote from: Shamrock (12 years ago)
I know that the diameter of a microtubule is 25 nm, but my homework is to show the work calculating this.  I am at a total loss.  Could someone please show me how to calculate it?

I have never come across a question that asks you to precisely calculate the diameter. I always assumed that it was a predication based on the amino acid sequence that make up the microtubule structure. Could you state the question as its shown? Perhaps you're misunderstanding it? Not sure.
- Master of Science in Biology
- Bachelor of Science
Shamrock Author
wrote...
#2
12 years ago
The question is not on a worksheet or in a textbook.  It is just a challenge that our professor gave us in class one day.  He said that the diameter of a microtubule is 25 nm, and then he asked us to show him how one would perform the calculations to get that answer.
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#3
Staff Member
12 years ago
Quote from: Shamrock (12 years ago)
The question is not on a worksheet or in a textbook.  It is just a challenge that our professor gave us in class one day.  He said that the diameter of a microtubule is 25 nm, and then he asked us to show him how one would perform the calculations to get that answer.

Is this advanced biochemistry? Do you have peptide viewing software?
- Master of Science in Biology
- Bachelor of Science
Shamrock Author
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#4
12 years ago
It is advanced cell biology, but we are supposed to be able to calculate it without any outside software.  Do you think it maybe has something to do with figuring out the diameter of tubulin and then finding out how many pieces of tubulin are in each microtubule?
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#5
Staff Member
12 years ago
Yeah, that's a pretty good assumption. Microtubules are hollow, cylindrical structures, approximately 30 nm in diameter, formed from tubulin, a dimeric protein composed of two similar 55-kD subunits known as a-tubulin and b-tubulin. Eva Nogales, Sharon Wolf, and Kenneth Downing have determined the structure of the bovine tubulin ab dimer to 3.7 angstrom resolution. Tubulin dimers polymerize to form microtubules, which are essentially helical structures, with 13 tubulin monomer “residues” per turn.

http://web.virginia.edu/Heidi/chapter17/Images/8883n17_02.jpg

http://web.virginia.edu/Heidi/chapter17/Images/8883n17_02a.jpg

(a) The structure of the tubulin alpha_beta heterodimer. (b) Microtubules may be viewed as consisting of 13 parallel, staggered protofilaments of alternating alpha-tubulin and beta-tubulin subunits. The sequences of the a and b subunits of tubulin are homologous, and the alpha_beta tubulin dimers are quite stable if Ca2+ is present. The dimer is dissociated only by strong denaturing agents.
- Master of Science in Biology
- Bachelor of Science
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