Biology And Biomedical Sciences BIOL 2960 Lecture Notes - Lecture 7: Disulfide, Carboxylic Acid, Proline
13 Dec 2016
School
Department
3 February 2016
Lectures 7: Proteins
I. Protein Basics
A. Amino Acids
1. Amino acids have a net neutral charge and 19 of the 20 amino acids (AAs) are chiral
(with the exception of glycine)
a. Mainchain or backbone of the amino acid structure is repeating N-C-C (per
residue)
2. There are various groups of amino acids (below taken from L6 notes)
a. Nonpolar hydrophobic (have lots of hydrocarbons)
• Gly (glycine, G), Ala (alanine, A), Val (valine, V), Leu (leucine, L), Ile
(isoleucine, I), Met (methionine, M), Pro (proline, P), Phe (phenylalanine, F),
Trp (tryptophan, W)
b. Polar, uncharged (have polar groups)
• Ser (serine, S), Thr (threonine, T), Tyr (tyrosine, Y), Cys (cysteine, C), Asn
(asparagine, N), Gln (glutamine, Q)
c. Basic (+) charged at physiological pH
• Lys (lysine, K), Arg (argenine, R), His (histine, H)
d. Acidic (-) charged at physiological pH
• Glu (glutamic acid, E), Asp (aspartic acid, D)
e. 3 special cases
• Gly (glycine, non-chiral, has just –H as the side chain)
• Cys (cysteine contains a thiol group and can form disulfide bridges- covalent)
• Pro (proline) side chain comes back to connect to amino group
(conformational restriction preventing N from forming more H-bonds)
3. The Peptide Bond
a. Notice that peptides have directionality: the end with the amino group is the “N-
terminus” and the end with the carboxyl group is the “C-terminus”
b. The peptide bond is formed in a condensation reaction between two adjacent
AAs, the water comes from the oxygen off the (de-protonated) carboxyl group
and 2 hydrogens off the (protonated) amino group
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