Amino acids Flashcards
define: a-amino acid
NH2 on the same carbon as COOH
how many aa’s havve atleast one stereocentre (ie are chiral)
all but one (glycine - H R group)
how many aa’s have d confi?
all but 2 - cysteine has L, glycine doesnt have any.
describe aa structure
R group - polar (also acidic and basic), non polar
H
COOH
NH2
aa’s are most accurately represented as
zwitterions
define: isoelectric point
pH at which most aa’s are in zwitterion form
describe how electrophoresis of aa’s relates to pH
paper and +/- electrodes dried and ninhydrin dye is aded to make aa's appear purple -higher charge density = moves quicker -goes to opposite pole -zwitterions dont move
pI (isoelectric point) calculation?
1/2(pKa1 + pKa2)
define: peptide
short polymer of aa’s joined by peptide bond
whats peptide bond
C-N in the condensation polymerised aa
define: polypeptide
multiple aa’s joined by peptide bonds
define: protein
biomacromolecule weighing atleast 5000gmol-1 and consists of atleast 1 pp chain
ways we determine sequence of aas
cyanogen bromide
enzyme catalysis
edman degradation
escribe cyanongen bromide
cleaves peptide bond formed by COOH of methionine
describe enzyme catalysis
hydrolyse specific bonds at cOOH
- trypsin: COOHs of arginine and lysine
- chymotrypsin: cleaves phenylalanine, tyrosine, tryptophan
describe edman degradation
identifies N terminal by attaching to N terminal of aa, cleaves itself and aa and aa’s identified. process repeats
priamry structure
sequence of aa’s contains peptide bonds
describe tertiary structure
overall folding pattern and arrangement of all atoms in a single pp chain
- by R groups
- cysteine reaction is reversible
define: quaternary structure
arrangement of pp chains into a non covalently bonded aggregration: can include additional units (eg. haem)
describe secondary structure
localised folding and coiling of pp chains
more on secondary strucutre?
yes
