post translational modifications Flashcards
protein folding
polypeptide chains spontaneously coils and folds into three-dimensional shape- consequence of its amino acid sequence-primary structure
why do proteins require post-translational modifications ?
to make them functional
N-terminal or C-terminal modification
formyl group or entire fMet residue removed in bacteria.
Met may be removed in eukaryotes
1-2 N- and C-terminal amino acids might be removed
proteins synthesized by cytosolic ribosomes can ?
- remain within cytosol
- be moved to proper cellular destinations
function of protease ?
an enzyme that catalyses the breakdown of proteins into smaller polypeptides
signal peptides
15-30 amino acids long
located at N-terminal of some proteins
direct protein to correct location
what are signal peptides cleaved by ?
signal peptidase
when does proteolytic processing occur ?
when a protease cleaves a protein to modify its activity
converting preproinsulin to insulin
signal sequence removed
disulfide bonds form (proinsulin)
C-peptide removed
Final product: A chain (21AA) and B chain (30AA)
what is thrombin
is a protease that converts soluble fibrinogen into insoluble strands of fibrin
blood clotting process
thrombin cleaves fibrinogen
forms mesh trapping platelets and red blood cells
where does fibrinogen circulate ?
in the blood
phosphorylation :
Ser/thr/tyr residues undergo phosphorylation in response to intra- and extra- cellular signals
characteristics of phosphorylation
regulates protein activity
can increase or decrease protein function
reversible process
what protein is hydroxylation specific to ?
collagen
hydroxylation
adding OH group
glycosylation
oligosaccharide addition
two types: N- linked and O-linked
N-linked glycosylation
added to asparagine
O-linked glycosylation
added to serine/threonine
