Deck 32: Completing the Protein Life Cycle: Folding, processing, and Degradation

Question 1

Which of the following ribosomal bound molecule helps avoid non-productive protein folding during transfer to DnaK?

A)chaperonin
B)trigger factor
C)Hsp40
D)Hsp70

Answer 1

B

Question 2

Which of the following types of sequences is required for proteins to remain embedded in the ER membrane with their C-termini on the cytosolic face of the ER?

A)translocator
B)leader
C)translocational
D)stop-transfer

Answer 2

D

Question 3

Which of the following receives partially folded protein intermediates during chaperone-dependent folding?

A)chaperonin
B)Hsp40
C)Hsp60
D)Hsp70

Answer 3

A

Question 4

Which of the following,together with signal recognition particles,deliver the nascent protein chain to specific membrane complexes that mediate integration into and across the membrane?

A)signal receptors
B)translocons
C)Golgi
D)ribosomes

Question 5

Eukaryotic secretory proteins are synthesized and translocated via the endoplasmic reticulum.Which of the following steps is part of this process?

A)signal sequence phosphorylation
B)glycosylation in the ER lumen
C)signal sequence addition
D)ribosome assembly

Question 6

Mitochondrial pre-sequences are positively charged amphipathic sequences retained in the unfolded stage.With which of the following molecular chaperones do they associate?

A)Hsp40
B)Hsp70
C)chaperonin
D)Hsp90

Question 7

Which of the following is a characteristic of chaperonin?

A)formed of 3 stacked rings of subunits
B)allows folding to proceed in a unprotected environment
C)small,cylindrical protein complexes
D)sequesters partially folded proteins

Question 8

Which of the following is a characteristic of protein translocation systems?

A)Translocons passively move proteins across the membrane.
B)Proteins to be translocated are made as preproteins containing distal blocks of amino acid sequences that act as sorting signals.
C)Membranes involved in translocation have specific protein receptors exposed on their cytosolic faces.
D)Pre-proteins are maintained in a tightly folded,translocation-competent conformation through interaction with molecular chaperones.

Question 9

Which of the following is a characteristic of Hsp90 chaperones?

A)They comprise more than 20% of total cytosolic proteins in eukaryotes.
B)Their action depends on cyclic binding and hydrolysis of GTP.
C)They direct proteins toward degradation pathways.
D)Their major purpose is conformational regulation of signal transduction molecules.

Question 10

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

A)polyglutamine aggregates
B)neurofibrillary tangles of polymeric microtubule-binding protein tau
C)extracellular deposits of amyloid-b and intracellular neurofibrillary tangles of microtubule-binding protein tau
D)mutations in the huntingtin gene

Question 11

Which of the following helper proteins assist nascent (newly formed)proteins to fold?

A)molecular chaperones
B)transcription factors
C)molecular principals
D)amyloids

Question 12

Which of the following pairs forms a common conduit for transfer of the nascent protein through the endoplasmic reticulum membrane?

A)ribosome and translocon
B)signal sequence and plasma membrane
C)EF-G and endoplasmic reticulum
D)chaperonin and plasma membrane

Question 13

Which of the following contains the information required for proper protein folding?

A)the primary structure
B)the amino acid content
C)the content of hydrophobic amino acids
D)the content of basic amino acids

Question 14

Which of the following statements concerning protein folding is correct?

A)The GroES protein serves as the cap for GroEL.
B)The Hsp70 proteins bind to hydrophilic regions of the protein,thus preventing aggregation.
C)The Hsp60 proteins are rarely known as chaperonins.
D)The GroEL protein provides an environment that leads to possible aggregation.

Question 15

Which of the following is the primary function of Met-aminopeptidase?

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

Question 16

Which of the following are the primary driving forces for protein folding?

A)hydrogen bonds
B)van der Waals interactions
C)hydrophobic interactions
D)electrostatic interactions

Question 17

Which of the following is NOT a characteristic of the mammalian translocon?

A)It has Sec61 complex at the core.
B)It is a transmembrane,protein-conducting channel.
C)BiP carries out ATP-dependent protein folding.
D)It is composed of a single transmembrane-spanning (TMS)protein.

Question 18

Which of the following is a part of the folding cycle in the GroES-GroEL complex of E.coli?

A)GroES promotes GTP hydrolysis,and a-subunits undergo a conformational change that buries the hydrophobic patches.
B)GroES associates to the complex.
C)Partially folded,protein hydrophilic residues bind GroEL.
D)GroES is recruited to GroEL.

Question 19

Which of the following is the most common form of posttranslational processing?

A)carbohydrate addition
B)proteolytic cleavage
C)lipid addition
D)phosphorylation

Question 20

Which of the following processes has proteolytic cleavage been shown to be involved with?

A)inactivation of regulatory enzymes
B)elimination of disulfide bridges
C)activation of zymogens
D)elimination of large protein sequences after the protein has reached its proper location

Question 21

Which of the following is NOT correct regarding the protein degradation process involving ubiquitin?

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.

Question 22

Which of the following does NOT occur during ubiquitination degradation of proteins?

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 C-terminal amino acid.
D)Ubiquitin-carrier protein (E2)picks up ubiquitin.

Question 23

Which of the following describes the functional role of the 19S cap in proteasome?

A)disposal
B)regulatory
C)ubiquitination complex
D)electron transport

Question 24

Which of the following is a highly conserved protein that is involved in protein degradation?

A)Met-aminopeptidase
B)ubiquitin
C)degradase
D)peptidyl transferase

Question 25

Which of the following amino acids in a protein targeted for destruction is most commonly the receptor for ubiquitin?

A)Ser
B)Lys
C)Asn
D)Tyr

Question 26

Which of the following is a characteristic of HtrA proteases?

A)chaperones at low temperatures
B)ATP-dependent
C)proteases at low temperatures
D)bind folded proteins

Question 27

In which of the following macromolecular structures is protein degradation compartmentalized?

A)ribosomes and endoplasmic reticulum
B)ribosomes and Golgi
C)proteasomes and mitochondria
D)proteasomes and lysosomes

Question 28

Which of the following is the proper sequence for transport of inner mitochondrial membrane proteins?

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