Amino Acids, Peptides, Proteins Flashcards
Stereochemistry
The stereochemistry of the a-carbon is L for all chiral
amino acids in eukaryotes. (carbohydrates are D-config).
All chiral amino acids except cysteine have (S)
configuration and all amino acids are chiral except for
Glycine.
Amphoteric
Amino acids can act as a base or an acid.
pKa
The pH at which half of the species is deprotonated;
[HA] = [A-
].
Dipeptide:
2 residues
Tripeptide:
3 residues
Oligopeptides:
Less than 20 residues
Polypeptides:
Greater than 20 residues
Formation of a Peptide bond
Forming a peptide bond is a dehydration reaction. The
nucleophilic amino group of one amino acid attacks the
electrophilic carbonyl group of another amino acid.
Amide Bonds
The C-N bond of a peptide bond. Rigid due to resonance.
Breaking peptide bonds
Breaking a peptide bond is a hydrolysis reaction.
1° Structure:
Linear sequence of amino acids in a peptide. Stabilized by
peptide bonds. The AA sequence is written N-terminus to Cterminus. N-terminus is POSITIVELY charged due to –NH3
+.
2° Structure:
The local structure of neighboring amino acid. Is stabilized
by hydrogen bonding between amino groups and
nonadjacent carboxyl groups.
a-helices:
: A common 2° structure. Clockwise coils around a central axis.
b-pleated
sheets:
A common 2° structure. Rippled strands that can be parallel
or antiparallel.
The effects of proline on secondary structure
Can interrupt secondary structure because of its rigid cyclic structure