# Volume of amino acids

1. Sep 8, 2010

### Krazer101

1. The problem statement, all variables and given/known data
Estimate the volumes of the various amino acids in units of nm^3

2. Relevant equations
V = 4/3*pi*r^3

3. The attempt at a solution
Is it alright to treat the amino acids as spheres? Using this I was thinking of measuring the distance, atomic radii and bond length, between end of R group and C terminus. Is this the right way to go or am I missing the problem completely?

2. Sep 8, 2010

### Staff: Mentor

Assumption about spheres won't hold. But I think you are right that some combination of bond length and atomic radii is the way to go. My guess is that nobody expects exact answer, you are just expected to be creative and find a reasonable way of finding the answer that will be in a correct ballpark.

3. Sep 8, 2010

### granpa

I'd just calculate the volume of the individual atoms and add them up
It wont be very accurate (because of overlapping electron orbitals) but I dont think its meant to be

hint:watch out for hydrogen

4. Sep 8, 2010

### Staff: Mentor

That was my first thought, I just decided to not post it :tongue2:

5. Sep 8, 2010

### Krazer101

I was thinking along the lines of that too, but I was just wondering if there was a better solution. The book solved many of the estimation problems by fitting the molecule, atom, etc into a 3-D shape, so I was thinking along those lines. Thank you for the help though, its much appreciated.

6. Sep 8, 2010

### Staff: Mentor

Fitting into 3-D shape is a good idea, but sphere won't work for all amino acids - for example phenylalanine has rather bulky and flat ring attached.