Module 9

Question 1

Protein insertion into the mammalian ER membrane is typically

Answer 1

cotranslational.

Question 2

Signal sequences that direct proteins to the ER membrane are:

Answer 2

Stretches of hydrophobic amino acids located generally located near the amino terminus of the protein

Question 3

___________ provides the driving force for translocating a polypeptide chain into the ER post-translationally.

Answer 3

ATP hydrolysis by BiP

Question 4

N-linked oligosaccharides are:

Answer 4

Added in the ER and modified in the Golgi

Question 5

GPI anchored membrane proteins are membrane associated by

Answer 5

a covalently attached lipid.

Question 6

The topology of membrane proteins can often be predicted by computer programs that identify ________________________________________ topogenic segments.

Answer 6

hydrophobic

Question 7

During N-glycosylation of proteins, an oligosaccharide precursor is first synthesized with _______sugar residue (s) and this preformed precursor is later transferred to the nascent polypeptide chain.

Answer 7

14

Question 8

Which of the following is a lectin?

Answer 8

calnexin

Question 9

Proteins that do not fold properly in the ER lumen are degraded in the cytosol by

Answer 9

the proteasome.

Question 10

Sorting of protein to mitochondria is

Answer 10

post-translational.

Question 11

Tom/Tim protein complexes are involved in

Answer 11

protein translocation into mitochondria.

Question 12

Sequences that target proteins to mitochondria are located at

Answer 12

the N-terminus of the precursor protein.

Question 13

Protein import into the mitochondrial matrix is supported by energy input from

Answer 13

ATP hydrolysis by chaperone proteins in the cytosol.
ATP hydrolysis by chaperone proteins in the mitochondrial matrix.
the proton-motive force across the inner mitochondrial membrane.

Question 14

Many peroxisomal matrix proteins are imported as

Answer 14

folded proteins.

Question 15

The nuclear pore complex allows for

Answer 15

passive diffusion of smaller molecules, import of proteins, active transport of very large molecules

Question 16

The nuclear transport receptor can bind to:

Answer 16

FG nucleoporins, Ran·GTP, basic nuclear localization signals in cargo proteins

Question 17

Which of the following is true about targeting of a secretory proteins?

Answer 17

The signal recognition particle (SRP) binds to the signal peptide soon after it appears outside the ribosome.

Question 18

The amino acid sequences that target proteins to chloroplasts, mitochondria and nuclei have the following property in common:

Answer 18

When added in the proper context, they are sufficient to direct the targeting of a foreign proteins into the respective organelles

Question 19

Glycosylation of proteins inside the endoplasmic reticulum does not involve:

Answer 19

a His residue on the protein.

Question 20

ER Type-I transmembrane proteins possess all of the following :

Answer 20

cleavable signal sequence, internal signal-anchor sequence, internal stop-transfer sequence

Question 21

Elucidate three different pathways for targeting proteins to the mitochondrial inner membrane.

Answer 21

inner membrane single pass, matrix, inner membrane multipass

Question 22

What is the meaning of “quality control in the ER?” Describe the unfolded-protein response. What is the fate of unassembled or misfolded proteins present in the ER?

Answer 22

BiP -> Ire1 -> Hac1 upregulate chaperones

Question 23

Describe the typical principles used to identify topogenic sequences within proteins and how these can be used to develop computer algorithms. How does the identification of topogenic sequences lead to prediction of the membrane arrangement of a multipass protein? What is the importance of the arrangement of positive charges relative to the membrane orientation of a signal anchor sequence?

Answer 23

Hydrophobicity determines membrane spanning-region, positive charge indicates cytosolic side of stop-transfer sequence

Question 24

List the post-translational modifications that occur in the ER. Why are bacteria often a poor choice for the production of proteins for therapeutic purposes?

Answer 24

Glycosylation, Disulfide isomerase and chaperone folding, cleavage

Question 25

To what extent do peroxisomal matrix protein import and peroxisomal membrane protein import share the same machinery?

Answer 25

Come from nuclear transcripts, but recognized and translocated by different proteins

Question 26

In multipass membrane proteins synthesized in association with membrane-bounded ribosomes of the rough ER, signal-anchor and stop-transfer anchor sequences alternate. What do these sequences do? Compare and contrast Type I, Type II and Type III ER membrane proteins.

Answer 26

type 1: signal sequence at amino end that is cleaved off, stop transfer designates cytosolic side
type 2: not cleaved, translocated from signal-anchor, C is in lumen, N is in cytosol
type 3: not cleaved, signal anchor, N in lumen, C in cytosol