Amino Acids, Peptides, Proteins Flashcards
(42 cards)
amino acids
four groups attached to a central (α) carbon; an amino group, a carboxylic acid group, a hydrogen atom, and an R group 20 appear in the proteins of eukaryotic organisms stereochemistry is L in eukaryotes, D can exist in prokaryotes hydrophobic - w/ long alkyl chains hydrophilic - w/ charges
R group
determines chemistry and function of that amino acid
cysteine
polar side chain only amino acid with (R) configuration
glycine
non-polar, non-aromatic side chain only amino acid that is not chiral has a H atom as its R group
non-polar, non-aromatic amino acids
glycine, alanine, valine, leucine, isoleucine, methionine, proline
aromatic
tryptophan, phenylalanine, tyrosine
polar
serine, threonine, asparagine, glutamine, cysteine
negatively charged (acidic)
aspartate, glutamate
positively charged (basic)
lysine, arginine, histidine
amphoteric
can accept or donate protons amino acids
pKa
pH at which half of the species is deprotonated [HA] = [A-]
zwitterion
neutral amino acid that exists at pH near the pI of the amino acid
isoelectric point (pI)
calculated by averaging the two pKa values of amino acid without a charged side chain
formation/breaking of peptide bond
condensation/hydration reaction–one molecule of water released 1. nucleophilic amino group of one amino acid attacks the electrophilic carbonyl group of another amino acid 2. amide bonds are rigid due to resonance hydrolysis reaction–one molecule of water added
primary structure
linear sequence of amino acids in a peptide and is stabilized by peptide bonds
secondary structure
local structure of neighboring amino acids, and is stabilized by hydrogen bonding between amino groups and nonadjacent carboxyl groups α-helices, ß-pleated sheets
α-helices
secondary structure of protein clockwise coils around a central axis
ß-pleated sheets
secondary structure of protein rippled strands that can be parallel or antiparallel
proline
non-polar, non-aromatic side chain can interrupt secondary structure because of its rigid cyclic structure
tertiary structure
three-dimensional shape of a single polypeptide chain, and is stabilized by hydrophobic interactions, acid-base interactions (salt bridges), hydrogen bonding, and disulfide bonds
hydrophobic interactions
tertiary structure of protein push hydrophobic R groups to the interior of a protein which increases entropy of the surrounding water molecules and creates a negative Gibbs free energy
disulfide bonds
occur when two cysteine molecules are oxidized and create a covalent bond to form cystine
quaternary structure
interaction between peptides in proteins that contain multiple subunits
prosthetic group
attached molecule of a conjugated protein may be a metal ion, vitamin, lipid, carbohydrate, or nucleic acid
