protein post-translational modification Flashcards
protein modification
takes place in the golgi apparatus
proteins are packaged into vesicles and tagged
can be modified during or after mRNA translation
proteins must carry a signal sequence/peptide to be modified
protein modification - proteolysis
cleaving the polypeptide allows the fragments to fold into different shapes
protein modification - covalent addition of molecules
acetyl group
methyl group
phosphate group
sugar moietes
lipid moietes
small peptides
proteolysis function
to make protein isoforms from a single mRNA
to activate a protein (zymogen > active form)
enhances proper protein folding
enhances insertion of proteins to membranes or lumen of organelles
protein localisation
insulin maturation
proteolysis example
preproinsulin > proinsulin > insulin
preproinsulin > proinsulin due to proteolysis of the signal sequence
proinsulin > insulin due to proteolysis of chain C
covalent modification examples
histone proteins
phosphorylation
ubiquitination
glycosylation
histone proteins
covalent modification example
acetylation > activation of a gene
methylation > inactivation of a gene
phosphorylation
covalent modification example
added phosphate groups alter the shape of the protein
addition of a phosphate group to serine, threonine and tyrosine residues of a protein by kinase enzymes to activate the protein
reversible process, removal of a phosphate group by phosphatase enzymes
e.g. CDK/cyclin complex
ubiquitination
covalent modification example
addition of ubiquitin to a protein to remove defective, non-functional proteins in the cell
signals proteins to the proteasome for degradation
glycosylation
covalent modification example
adding sugars is important for targetting and recognition
the addition of a sugar molecule to the side chains of amino acids to change the proteins conformation
N-linked > to the nitrogen atom of asparagine
O-linked > to the oxygen atom of serine and threonine
