amino acids

Question 1

Absolute configuration at the alpha carbon position

Answer 1

the alpha carbon in every amino acid is a chiral center (except in glycine, which is achrial)
every amino acid has S configuration except for cysteine, which is R configuration

Question 2

Effect of pH on amino acids

Answer 2

Amino acids are dipolar ions
at low pH they are positively charged (cationic)
at high pH they are negatively charged (anionic)
at pH=pI they are zwitterionic (neutral)

Question 3

acidic amino acids

Answer 3

aspartic acid (Asp, D) and glutamic acid (Glu, E)

Question 4

basic amino acids

Answer 4

histidine (His, H), arginine (Arg, R), and lysine (Lys, K)

Question 5

polar amino acids

Answer 5

cysteine (Cys, C), asparagine (Asn, N), gutamine (Gln, Q), threonine (Thr, T), serine (Ser, S), and tyrosine (Tyr, Y)
(CNQTS, Y?)

Question 6

non-polar amino acids

Answer 6

leucine (Leu, L), isoleucine (Ise, I), methionine (Met, M), proline (Pro, P), valine (Val, V), alanine (Ala, A), glycine (Gly, G), phenylalanine (Phe, F), and tryptophan (Trp, W)

Question 7

sulfur linkage

Answer 7

disulfide bond forms between two cysteins

Question 8

peptide linkage

Answer 8

peptide bonds link amino acids together
formed by nucleophilic addition-elimination (condensation / dehydration reaction) between the carboxyl group of one amino acid and the amino group of another amino acid
nucleophilic amino group attacks the electrophilic carbonyl
peptide bond has resonance delocalization, making bond rigid and planar although there is still free rotation around the alpha carbon

Question 9

hydrolysis

Answer 9

reaction that breaks peptide bond
nonspecific: acid/base hydrolysis breaks bond
specific: proteolytic enzymes break bond