Post-translational modifications Flashcards
What is meant by post-translational modifications?
Processing that proteins undergo after translation
What are the types of post-translational modifications?
Proteolytic cleavage
Chemical modification
What is meant by proteolytic cleavage?
Breaking peptide bonds to remove part of the protein
What is meant by chemical modification?
Additional of function groups to protein
What are some examples post-translational modifications that occur in the ER?
Proteolytic cleavage
Forming disulphide bonds
N-linked glycosylation
Hydroxylation
Disulphide bonds are formed between what amino acid?
Cysteine
What is the enzyme responsible for forming disulphide bonds?
Protein disulphide isomerase
What is glycosylation?
Addition of sugar molecules to amino group -NH2
What is hydroxylation?
Addition of hydroxyl group -OH to protein
What is an example of a modification that occur in the Golgi apparatus?
O-linked glycosylation
What is O-linked glycosylation?
Attachment of sugar to hydroxyl group -OH
What is the importance of glycosylation?
Correct protein folding
Interaction with other molecules
What do problems with glycosylation lead to?
Congenital disorders of glycosylation, CDGs
What is produced when the mRNA of the insulin gene is translated?
Preproinsulin
Which ribosomes produce insulin?
Ribosomes on the ER
What happens to preproinsulin in the ER?
Signal peptide is cleaved off to form proinsulin
2 disulphide bonds formed bewtwen A chain and B chain
1 disulphide bond formed at A chain
Where is proinsulin transported to form the ER?
Golgi
What happens to proinsulin in the Golgi?
C chain is cleaved off to produce insulin
How does proteolytic cleavage create different proteins?
Cleavage at different sites
can produce different proteins of different lengths
What can cause misfolding of a protein?
Mutations in gene producing protein with different amino acid sequence primary structure
Protein trapped in misfolded conformation
What is responsible for correcting misfolded proteins?
ER chaperone proteins
What happens to a misfolded protein if it cannot be corrected by ER chaperone proteins?
Protein returned to cytosol for degradation
Protein accumulates in ER, causing disease
What are the types of secretion?
Constitutive
Regulatory
What is constitutive secretion?
Proteins being continuously secreted
What is regulated secretion?
Proteins secreted when they are needed
What are the three examples of proteins secreted constitutively?
Collagen
Albumin
Immunoglobulin
What are three examples of proteins secreted regularly?
Insulin
Glucagon
ACTH
