Protein Synthesis II

Question 1

What is the function of chaperones?

Answer 1

Mediate proper folding of proteins

Hsp70 family are ATP-dependent

Bind and cover hydrophobic patches

Question 2

What is the function of protein disulfide isomerases?

Answer 2

Catalyzes the formation and cleavage of disulfide bonds

Question 3

What is the function of peptidyl prolyl isomerase?

Answer 3

Catalyze the transition of proline residues between the cis and trans configurations

Question 4

What are the three mechanisms of proteolytic processing?

Answer 4

• Removal of the initiator methionine at the N-terminus
• Cleavage of large precursors to form active enzymes or hormones
• N-terminal signal sequence cleavage

Question 5

How is mature insulin formed?

Answer 5

Cleavage of a signal peptide and internal peptide

Question 6

What is co-translational translocation?

Answer 6

The active translation of proteins into the ER lumen via the rough ER.

Question 7

What is N-linked glycosylation?

Answer 7

Linkage of a carbohydrate to asparagine in the ER?

Question 8

What is O-linked glycosylation?

Answer 8

Linkage of a carbohydrate to a serine or threonine residue in the golgi apparatus

Question 9

What are calnexin and calreticulin?

Answer 9

Chaperone proteins that bind N-linked residue site when one glucose remains and stops binding when the last glucose is removed.

Question 10

What is the role of the folding sensor protein?

Answer 10

Determines if the protein is correctly folded or not.

Adds glucose back if not properly folded

Question 11

What is the role of glycosylphosphatidylinositol (GPI) anchors?

Answer 11

Attach proteins to the luminal side of the ER membrane.

Will eventually end up on the outside of the cell

Question 12

What is N-myristoylation?

Answer 12

Attachment of myristic acid to an N-terminal glycine residue.

Glycine is exposed by the removal of the initiating met residue

Question 13

What is palmitoylation?

Answer 13

Palmitic acid added to an internal cysteine residue

Question 14

What is the role of serine/threonine and tyrosine kinases?

Answer 14

Phosphorylation of specified residues on proteins

Question 15

What is the role of serine/threonine and tyrosine phosphatases?

Answer 15

Dephosphorylation of specifed residues on proteins

Question 16

What is nitrolysation?

Answer 16

Addition of NO groups to internal cysteine residues

Catalyzed by (de)Nitrosylases

Question 17

What is the unfolded protein response?

Answer 17

An excess of unfolded proteins leads to the expansion of the ER, production of more chaperones, and apoptosis in extreme cases.

Question 18

What is the function of IRE1?

Answer 18

Receptor that recognizes unfolded proteins and activates XP1 transcription factors

Question 19

What is the function of ATF6?

Answer 19

Receptor that recognizes ATF6, and cleaves, releasing ATF6 as a transcription factor

Question 20

What is the function of PERK?

Answer 20

Recognizes unfolded proteins and phosphorylates eIF2, blocking translation

Leads to the activation of ATF4 TF

Question 21

What is the function of XP1, ATF6, and ATF4?

Answer 21

TFs that target genes that encode chaperones, lipid synthesis enzymes, and ERAD proteins

Question 22

How are proteins degraded?

Answer 22

Ubiquitinated by Ubiquitin ligase.

Degree of ubiquitination determines the likelihood of degradation

Question 23

What are prion disorders?

Answer 23

infection with misfolded protein that stimulates other proteins to misfold.

Jakob-Crutzfeld, Kuru, Scrapie, Mad Cow