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Homework answers / question archive / Chapter 31--Completing the Protein Life Cycle: Folding, Processing, and Degradation  1)The information for folding each protein into its unique three-dimensional architecture resides within its ____

Chapter 31--Completing the Protein Life Cycle: Folding, Processing, and Degradation  1)The information for folding each protein into its unique three-dimensional architecture resides within its ____


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


2. 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


3. 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


4. 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-b and intracellular neurofibrillary tangles of microtubule-binding protein tau
D. mutation in the huntingtin gene
E. none of the above


5. 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


6. 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


7. All are characteristics of chaperonins EXCEPT: 
A. allow folding to proceed in a protected environment.
B. large, cylindrical protein complexes.
C. sequester partially folded proteins.
D. formed of two stacked rings of subunits.
E. all are true.


8. The folding cycle in the GroES-GroEL complex of E. coli utilizes the following sequence:


ATP binding to GroEL


GroES dissociates from the complex


Partially folded protein hydrophobic residues bind GroEL


GroES is recruited to GroEL


GroES promotes ATP hydrolysis and a-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


9. 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


10. 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.


11. The most common form of post-translational processing is: 
A. carbohydrate addition.
B. lipid addition.
C. phosphorylation.
D. adding signal sequences.
E. proteolytic cleavage.


12. 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.


13. 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.


14. 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.


15. ____ 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


16. Eukaryotic secretory proteins are synthesized and translocated via the endoplasmic reticulum. Order the following sequence of events for this process.


signal sequence removed.


glycosylation in the ER lumen.


signal sequence synthesis on ribosomes.


SRP binds signal sequence and subsequently binds SRP-receptor.


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


17. 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


18. 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.


19. 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


20. 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


21. The proper sequence for transport of inner mitochondrial membrane proteins would be: 


22. 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. proteosomes; lysosomes
E. lysosomes; endoplasmic reticulum


23. A highly conserved protein that is involved in protein degradation is: 
A. ricin
B. met-aminopeptidase
C. ubiquitin
D. degradase
E. peptidyl transferase


24. 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.


25. The appropriate sequence for ubiquitination of proteins to be degraded is:


multiple ubiquitinations may occur on a protein substrate,


ubiquitin-protein ligase (E3) transfers ubiquitin to free amino groups on the protein,


E3 selects a protein for degradation by the nature of the N-terminal amino acid,


ubiquitin-carrier protein (E2) picks up ubiquitin,


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


26. Which amino acid in a protein targeted for destruction is most commonly the receptor for ubiquitin? 
A. Ser
B. Lys
C. Asn
D. Tyr
E. His


27. 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


28. 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.


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