During lecture, the professor asked why valine does not have two carbons that stick off of it but more?
"Hydrophobic amino acids
Starting with glycine. Glycine is the smallest amino acid - and as a matter fact, it is only a hydrogen, which means that there's no stereocenter on the alpha carbon of glycine. It takes up very little space in protein chains and is good for tight corners and things. Alanine, a very simple straightforward CH3 sticking off of that alpha carbon, that is a nonpolar, hydrophobic group, but it's very small also. Valine is a little bit bigger. Why don't they have one that's just two carbons sticking off of it? Very interesting question. I don't know the answer to that. But basically, it's the same thing as the alanine, just larger. It's a hydrophobic group, it just takes up space. The same could be said for leucine - another carbon has been added on leucine, and the shape is a little bit different. Isoleucine is an isomer of leucine, which we get the name from, if you want to remember, which one is leucine and which one is isoleucine, I just remember at the top of the leucine, the three carbons there make a little "L" and on the top of the isoleucine, the two carbons make a little "I" and the next three carbons make a little "L", so it would be "L" and "IL", in case you're curious about that. "
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