Post-translational modifications

Question 1

What is meant by post-translational modifications?

Answer 1

Processing that proteins undergo after translation

Question 2

What are the types of post-translational modifications?

Answer 2

Proteolytic cleavage

Chemical modification

Question 3

What is meant by proteolytic cleavage?

Answer 3

Breaking peptide bonds to remove part of the protein

Question 4

What is meant by chemical modification?

Answer 4

Additional of function groups to protein

Question 5

What are some examples post-translational modifications that occur in the ER?

Answer 5

Proteolytic cleavage

Forming disulphide bonds

N-linked glycosylation

Hydroxylation

Question 6

Disulphide bonds are formed between what amino acid?

Answer 6

Cysteine

Question 7

What is the enzyme responsible for forming disulphide bonds?

Answer 7

Protein disulphide isomerase

Question 8

What is glycosylation?

Answer 8

Addition of sugar molecules to amino group -NH2

Question 9

What is hydroxylation?

Answer 9

Addition of hydroxyl group -OH to protein

Question 10

What is an example of a modification that occur in the Golgi apparatus?

Answer 10

O-linked glycosylation

Question 11

What is O-linked glycosylation?

Answer 11

Attachment of sugar to hydroxyl group -OH

Question 12

What is the importance of glycosylation?

Answer 12

Correct protein folding

Interaction with other molecules

Question 13

What do problems with glycosylation lead to?

Answer 13

Congenital disorders of glycosylation, CDGs

Question 14

What is produced when the mRNA of the insulin gene is translated?

Answer 14

Preproinsulin

Question 15

Which ribosomes produce insulin?

Answer 15

Ribosomes on the ER

Question 16

What happens to preproinsulin in the ER?

Answer 16

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

Question 17

Where is proinsulin transported to form the ER?

Answer 17

Golgi

Question 18

What happens to proinsulin in the Golgi?

Answer 18

C chain is cleaved off to produce insulin

Question 19

How does proteolytic cleavage create different proteins?

Answer 19

Cleavage at different sites

can produce different proteins of different lengths

Question 20

What can cause misfolding of a protein?

Answer 20

Mutations in gene producing protein with different amino acid sequence primary structure

Protein trapped in misfolded conformation

Question 21

What is responsible for correcting misfolded proteins?

Answer 21

ER chaperone proteins

Question 22

What happens to a misfolded protein if it cannot be corrected by ER chaperone proteins?

Answer 22

Protein returned to cytosol for degradation

Protein accumulates in ER, causing disease

Question 23

What are the types of secretion?

Answer 23

Constitutive

Regulatory

Question 24

What is constitutive secretion?

Answer 24

Proteins being continuously secreted

Question 25

What is regulated secretion?

Answer 25

Proteins secreted when they are needed

Question 26

What are the three examples of proteins secreted constitutively?

Answer 26

Collagen

Albumin

Immunoglobulin

Question 27

What are three examples of proteins secreted regularly?

Answer 27

Insulin

Glucagon

ACTH