Biochemistry Flashcards
Amino acid structure
4 groups attached to a central carbon: amino, carboxylic acid, hydrogen atom, R group; All are chiral except glycine; are amphoteric (can accept or donate protons)
Stereochemistry of alpha carbon in amino acids
L; D-amino acids in prokaryotes
Nonpolar, nonaromatic amino acid sidechains
glycine, alanine, valine, leucine, isoleucine, methionine, proline
Aromatic amino acid sidechains
tryptophan, phenylalanine, tyrosine
Polar amino acid side chains
serine, threonine, asparagine, glutamine, cysteine
Negatively charged amino acid aide chains
aspartate, glutamate
Positively charged amino acid side chains
lysine, arginine, histidine
Isoelectric point (pI)
pH at which molecule is electrically neutral; average pKa values of amino and carboxyl groups
pKa
pH at which half of the species are deprotonated; pKa = -logKa
zwitterion
Has a positive and negative charge, is electrically neutral
Peptide bond formation
Condensation/dehydration reaction; Nucleophilic amino group of one amino acid attacks electrophilic carbonyl group of another amino acid
Primary protein structure
Linear sequence of amino acids in a peptide and is stabilized by peptide bonds
Secondary protein structure
Local structure of neighboring amino acids; stabilized by H-bonding between amino groups and nonadjacent carboxyl groups; alpha-helices and beta-pleated sheets
Tertiary protein structure
3D shape of single polypeptide chain; stabilized by hydrophobic interactions, acid-base interactions (salt bridges), hydrogen bonding, and disulfide bonds
Quaternary protein structure
Interaction between peptides in proteins that contain multiple subunits
