Deck 31: Completing the Protein Life Cycle: Folding, Processing, and Degradation

Question 1

Nascent (newly formed) proteins are often assisted in folding and ____ by a family of helper proteins known as ____.

A) unfolding; molecular principals
B) refolding; molecular principals
C) refolding; molecular chaperones
D) unfolding; molecular chaperones
E) unfolding; amyloids

Answer 1

C

Question 2

The information for folding each protein into its unique three-dimensional architecture resides within its ____.

A) primary structure
B) amino acid content
C) content of hydrophobic amino acids
D) content of basic amino acids
E) none are true

Answer 2

A

Question 3

Proteins with ____ sequences remain embedded in the ER membrane with their ____-termini on the cytosolic face of the ER.

A) translocator; N
B) leader; C
C) translocational; N
D) stop-transfer; C
E) translocon; N

Answer 3

D

Question 4

The ribosome and the ____ form a common conduit for transfer of the nascent protein through the ____ membrane.

A) translocon; endoplasmic reticulum
B) signal sequence; plasma
C) EF-G; endoplasmic reticulum
D) chaperonin; plasma
E) all are true

Question 5

Mitochondrial presequences are ____ charged amphipathic sequences retained in the ____ stage through association with ____ molecular chaperones.

A) positively; folded; Hsp40
B) positively; unfolded; Hsp70
C) negatively; folded; Hsp70
D) neutral; unfolded; Hsp40
E) negatively; prefolded; Hsp90

Question 6

The primary driving force for folding is/are ____ and if crowding occurs then ____ is likely.

A) hydrogen bonding; dehydration
B) hydrogen bonding; non-specific bonding
C) hydrophobic interactions; aggregation
D) hydrophilic interactions; non-specific binding
E) none are true

Question 7

The most common form of post-translational processing is:

A) carbohydrate addition.
B) lipid addition.
C) phosphorylation.
D) adding signal sequences.
E) proteolytic cleavage.

Question 8

Proteolytic cleavage has been shown to be involved in all of the following processes EXCEPT:

A) inactivation of regulatory enzymes.
B) elimination of the N-terminal Met residue.
C) activation of zymogens.
D) elimination of signal sequences after the protein has reached its proper location.
E) digestion of dietary proteins.

Question 9

Which of the following is responsible for Alzheimer's disease?

A) polyglutamine aggregates
B) neurofibrillary tangles of polymeric microtubule-binding protein tau
C) extracellular deposits of amyloid-β and intracellular neurofibrillary tangles of microtubule-binding protein tau
D) mutation in the huntingtin gene
E) none of the above

Question 10

Characteristics of protein translocation systems include all EXCEPT:

A) proteins to be translocated are made as pre-proteins containing contiguous blocks of amino acid sequences that act as sorting signals.
B) membranes involved in translocation have specific protein receptors exposed on their cytosolic faces.
C) translocons catalyze movement of the proteins across the membrane and metabolic energy in the form of ATP, GTP, or membrane potential is essential.
D) pre-proteins are maintained in a loosely folded, translocation-competent conformation through interaction with molecular chaperones.
E) all are characteristics.

Question 11

In E. coli, ____ bound to large ribosomal subunits facilitates transfer to ____ to bind ____ residues, thus avoiding non-productive folding.

A) chaperonin; trigger factor; H-binding
B) trigger factor; DnaK; hydrophobic
C) DnaK; Hsp70; ionic
D) Hsp70; chaperonin; hydrophilic
E) all are true

Question 12

Characteristics of Hsp90 chaperones include all EXCEPT:

A) 1-2% of total cytosolic proteins in eukaryotes.
B) action depends on cyclic binding and hydrolysis of ATP.
C) major purpose is conformational regulation of signal transduction molecules.
D) directs proteins toward degradation pathways.
E) all are true.

Question 13

The folding cycle in the GroES-GroEL complex of E. coli utilizes the following sequence:
A)ATP binding to GroEL
B)GroES dissociates from the complex
C)Partially folded protein hydrophobic residues bind GroEL
D)GroES is recruited to GroEL
E)GroES promotes ATP hydrolysis and α-subunits undergo a conformational change that buries the hydrophobic patches

A) A, B, C, D, E
B) B, A, C, D, E
C) C, D, A, E, B
D) C, A, D, E, B
E) D, C, E, A, B

Question 14

Characteristics of the mammalian translocon include all EXCEPT:

A) sec61 complex at the core.
B) transmembrane protein-conducting channel.
C) BiP carries out ATP-dependent protein folding.
D) composed of a single transmembrane spanning (TMS) protein.
E) all are true.

Question 15

Which of the following statements regarding chaperones and chaperonins is correct?

A) GroEL serves as a cap for GroES
B) GroES is a large, cylindrical protein complex
C) DnaK works with DnaJ to sequester hydrophobic regions of peptides
D) while the GroEL-GroES complex requires ATP to aid in protein folding, the DnaK-DnaJ system does not
E) all are true.

Question 16

In general, proteins whose folding is chaperone-dependent start the folding process first with ____ and then are passed as ____ folded intermediates to ____.

A) Hsp40; un-; Hsp70
B) Hsp90; un-; chaperonin
C) Hsp70; partially; chaperonin
D) Hsp40; partially; Hsp70
E) Hsp60; partially; Hsp40

Question 17

Which of the following statements about protein folding is INCORRECT?

A) the Hsp70 proteins bind to hydrophilic regions of the protein, thus preventing aggregation
B) the Hsp60 proteins are also known as chaperonins
C) the GroEL protein provides an environment free from possibility of aggregation
D) the GroES protein serves as the cap for GroEL
E) all are correct

Question 18

____ recognize the sorting signals as they emerge from the ribosome and together with ____ deliver the nascent protein chain to specific membrane complexes called ____ that mediate integration into and across the membrane.

A) Signal recognition particles; signal receptors; translocons
B) Signal receptors; translocons; signal recognition particles
C) Translocons; signal recognition particles; signal receptors
D) Signal receptors; signal recognition particles; translocons
E) Translocons; signal receptors; signal recognition particles

Question 19

Eukaryotic secretory proteins are synthesized and translocated via the endoplasmic reticulum. Order the following sequence of events for this process.
A)signal sequence removeD.B.glycosylation in the ER lumen.
C)signal sequence synthesis on ribosomes.
D)SRP binds signal sequence and subsequently binds SRP-receptor.
E)ribosome dissociates.

A) A, C, E, B, D
B) C, D, A, B, E
C) C, A, D, B, E
D) A, C, B, D, E
E) C, B, D, E, A

Question 20

The primary function of Met-aminopeptidase is to:

A) cleave large inactive pro-proteins.
B) remove leader peptides after translocation.
C) transfer a Met to the C-terminal end for translocation.
D) remove invariable Met and introduce N-terminal diversity.
E) all are true.

Question 21

Which of the following proteins would be commonly ubiquitinated and thus degraded by the proteasome?

A) proteins with Met as the N-terminal amino acid
B) proteins with short sequences rich in Pro, Glu, Ser and Thr
C) proteins with short sequences rich in Trp, Thr, and Phe
D) proteins having a C-terminal Cys for the formation of a thioester bond with ubiquitin
E) none of the above

Question 22

Discuss the significance of proteolytic cleavage in post-translational processing.​

Question 23

Discuss the functions of HtrA proteases.​

Question 24

Discuss the structure of the chaperonin GroES-GroEL complex found in E. coli.​

Question 25

A highly conserved protein that is involved in protein degradation is:

A) ricin
B) met-aminopeptidase
C) ubiquitin
D) degradase
E) peptidyl transferase

Question 26

The proper sequence for transport of mitochondrial matrix proteins would be:

A) TOM; TIM22
B) TOM; TIM23
C) SAM; TOM; TIM22
D) TOM; SAM; TIM22
E) SAM; TOM; TIM23

Question 27

All are correct statements regarding the protein degradation process involving ubiquitin EXCEPT:

A) The modified protein is degraded by an ATP-dependent protease complex.
B) The ubiquitin binding to the protein to be degraded leads to a novel branched protein.
C) The ubiquitin is covalently attached to a cysteine residue in the protein to be degraded.
D) Three additional proteins (E₁, E₂, and E₃) are involved in the ligation of ubiquitin to the protein.
E) Ubiquitin is a highly conserved protein.

Question 28

​Explain how mitochondrial preproteins are imported into the mitochondria.

Question 29

What does Hsp (as in Hsp60) stand for?

A) helical stabilizing protein
B) hydrophobic sequestering protein
C) heat shock protein
D) high-histidine subunit protein
E) none of the above

Question 30

Protein degradation is compartmentalized either in macromolecular structures known as ____ or in degradative organelles such as ____.

A) ribosomes; endoplasmic reticulum
B) ribosomes; Golgi
C) proteosomes; mitochondria
D) proteasomes; lysosomes
E) lysosomes; endoplasmic reticulum

Question 31

In a protein targeted for destruction, ubiquitin is most commonly attached to a _____ residue, forming a/an ______ bond between ubiquitin and the targeted protein.

A) Ser; ester
B) Lys; amide
C) α-amine group of the N-terminal amino acid if the particular residue is Arg, Lys, His, Phe, Tyr, Trp, Leu, Asn, Gln, Asp or Glu; amide
D) Glu; acid anhydride
E) Cys; thioester

Question 32

Which of the following is a result of the sumoylation of a protein?

A) addition of SUMO targets a protein for destruction by a slightly different pathway than attachment of ubiquitin
B) addition of SUMO often changes the conformation of a protein so that it interacts with other proteins in a different manner
C) addition of SUMO targets a protein for transport into the mitochondria
D) the addition of SUMO occurs during the translation process and is meant to stall translation of certain proteins
E) none of the above

Question 33

Explain how the amino acids at the amino terminus determine the susceptibility of proteins to degradation through the ubiquitin pathway.​

Question 34

In the proteosomes, the 19S cap acts as a ____ complex for the recognition and selection of ____ proteins for ____ by the 20S proteosomes core.

A) hydrolysis; unfolded; disposal
B) regulatory; unfolded; disposal
C) hydrolysis; ubiquitinylated; degradation
D) regulatory; ubiquitinylated; degradation
E) all are true

Question 35

All are characteristics of HtrA proteases EXCEPT:

A) ATP-dependent.
B) chaperones at low temperatures.
C) proteases at high temperatures.
D) bind misfolded or unfolded proteins.
E) all are true.

Question 36

The appropriate sequence for ubiquitination of proteins to be degraded is:
A)multiple ubiquitinations may occur on a protein substrate,
B)ubiquitin-protein ligase (E₃) transfers ubiquitin to free amino groups on the protein,
C)E₃ selects a protein for degradation by the nature of the N-terminal amino acid,
D)ubiquitin-carrier protein (E₂) picks up ubiquitin,
E)ubiquitin-activating enzyme (E₁) attaches via ATP-dependent formation of thioester bond to C-termini of ubiquitin,

A) A, C, B, D, E
B) E, D, A, B, C
C) D, E, C, A, B
D) C, E, D, B, A
E) E, D, C, B, A