Deck 5: Protein Structure and Function

Question 1

The quaternary structure of a given protein is defined by which of the following?

A) linear order of the amino acids
B) ordered organization of secondary structures within the protein
C) organization of super-secondary structures within the protein
D) overall structure resulting from association of domains within the protein
E) structure resulting from the interactions between multiple polypeptide chains

Answer 1

structure resulting from the interactions between multiple polypeptide chains

Question 2

In an enzyme with a critical glutamic acid residue (Glu, E) in the active site, which of the following
Amino acid substitutions would be expected to have the least effect on enzyme activity?

A) Arg
B) Asp
C) Lys
D) Ser
E) Tyr

Answer 2

Asp

Question 3

A 12-year-old boy has suffered from chronic sinopulmonary disease including persistent infection of the airway with Pseudomonas aeruginosa. He has constant and chronic sputum production because of the airway infection. Additionally, he suffers from gastrointestinal (GI) and nutritional abnormalities that include biliary cirrhosis, meconium ileus, and pancreatic insufficiency. The symptoms are classical for which of the following disorders?

A) congenital adrenal hyperplasia
B) cystic fibrosis
C) renal Fanconi syndrome
D) sickle cell anemia
E) Tay-Sachs disease

Answer 3

cystic fibrosis

Question 4

You are examining the lipid-interaction characteristics of a particularly hydrophobic protein. Mutational studies with this protein have been designed to examine these lipid interaction properties. Addition of which of the following amino acids to the protein would most likely be expected to interfere with the lipid-interaction properties?

A) aspartate
B) glycine
C) isoleucine
D) leucine
E) valine

Question 5

You are examining digestive enzymes and their processes of activation. You have isolated a mutant form of one particular enzyme and found that it remains inactive in a mixture of digestive juices. The wild-type enzyme is normally activated by hydrolysis on the C-terminal side of Arg and Lys residues and you determine that the mutant enzyme contains Ser residues at these critical positions. Which of the following digestive enzymes is most likely responsible for activation of the wildtype enzyme in your studies?

A) aminopeptidase
B) carboxypeptidase
C) chymotrypsin
D) enteropeptidase
E) lysozyme

Question 6

You are studying the characteristics of membraneassociated proteins. You have isolated and characterized both wild-type and mutant forms of a particular protein. The mutant protein does not remain anchored in the plasma membrane. Which of the following properties results in membrane anchoring of the wild-type protein and is likely defective in the mutant version?

A) disulfide bond formation between the protein and its phosphatidylinositol anchor
B) extensive hydrogen bonding of the amino acid side chains of the protein and the membrane phospholipid tails
C) extensive hydrophobic interactions between the amino acid side chains of the protein and the membrane phospholipid tails
D) formation of ionic bonds between the amino acid side chains and the phospholipid tails
E) formation of β-pleated sheet structures to maximize protein interactions with the phospholipid head group

Question 7

You are examining the thermodynamically stable structures of proteins. In particular you are studying the α-helix and β-sheet conformations that form in the study proteins. These conformations correspond to which of the following?

A) native conformation
B) primary structure
C) secondary structure
D) tertiary structure
E) quaternary structure

Question 8

In the β-sheet structure of proteins, the hydrogen bond on the peptide bond nitrogen of one of the peptides will most likely form a hydrogen bond with which of the following?

A) hydrophilic side chains in the adjacent sheet segment
B) hydrophobic side chains in the adjacent sheet segment
C) peptide bond carbonyl in the adjacent sheet segment
D) peptide bond carbonyl within 3 amino acids of the same segment
E) water in the surrounding medium

Question 9

You have isolated a strain of cholera that does not induce the same symptoms in host organisms as
The wild-type pathogen. The toxin from wild-type cholera is known to cause diarrhea only after its 2 polypeptide subunits dissociate from each other. This dissociation occurs when the toxin enters an acid environment. You find that the strain you have isolated is not localized to a particular cellular location, which likely explains the lack of activity. In which of the following cellular locations are the wild-type toxin subunits most likely to dissociate from each other, thereby becoming active?

A) coated vesicle
B) cytosol
C) endosome
D) mitochondrial matrix
E) nucleus

Question 10

During the normal processes of the cell cycle, specific types of DNA-protein complexes form and dissociate which allow condensation and decondensation of the chromosomes. Which of the following is the major attractive force between the DNA and the proteins, allowing these complexes to form?

A) disulfide linkages
B) electrostatic interactions
C) hydrogen bonds
D) hydrophobic interactions
E) van der Waals forces

Question 11

You are studying the relationships between protein structure and function. You are most interested in
The characteristics of a family of proteins termed chaperones. Which of the following processes requires chaperone activity in order to facilitate correct biological function?

A) assembly of coated pits
B) correct folding of nascent proteins
C) formation of tight junctions
D) interaction between actin and myosin
E) processing of telomeres

Question 12

Digestive enzymes have been used in the study of protein structure. Which of the following explains
The usefulness of trypsin and chymotrypsin in studies of protein structure?

A) efficiency as exopeptidases
B) high specificity for particular peptide bonds
C) high stability because of the presence of disulfide cross-links
D) high turnover rates
E) rapid digestion of proteins to yield amino acids and small oligopeptides

Question 13

The peptide bond of all proteins forms with highly specific orientation. This orientation contains atoms linked in which of the following ways?

A) C-N-C-C
B) C-N-H-C
C) C-O-N-C
D) C-C-O-N
E) C-S-S-C

Question 14

You are studying the characteristics of protein secondary structure. You find that the protein you are examining forms an α-helical structure more rapidly in an alcohol medium than it does in water. Which of the following is the best explanation for this difference?

A) competition for hydrogen bonding is lower for ethanol than for water
B) ethanol forms covalent interactions with the peptide
C) hydrophobic forces are greater in ethanol than in water
D) the peptide aggregates in water but not in ethanol
E) van der Waals interactions are lower in ethanol than in water

Question 15

You are studying the protein-folding characteristics of a particular protein. You find that under certain conditions the protein does not fold correctly and it precipitates within the cytosol. Which of the following processes is most directly responsible for aggregation and precipitation of the misfolded protein in the cytoplasm?

A) attachment of palmitate to the C-terminus
B) exposure of hydrophobic residues on the surface of the protein
C) formation of incorrect disulfide bonds between pairs of cysteine residues
D) nonenzymatic glycosylation of amino groups by free glucose
E) phosphorylation of threonine or serine side chains

Question 16

Mutational studies on collagen proteins demonstrate that substitution of one particular amino acid significantly affects the normal structure of the collagen molecules. Which of the following amino acids is absolutely required for the stable formation of the collagen triple helix?

A) alanine
B) cysteine
C) glycine
D) phenylalanine
E) tryptophan

Question 17

The parents of a 3-year-old boy bring him to the hospital following a fall as they are concerned he has broken his arm. His parents report that over the past year he has had several episodes of what they think is uncharacteristically easy fractures in his legs from minor falls. They indicate that there is no family history of bone disease. Physical examination shows bowing and deformities of the legs, and x-rays show evidence of previous fractures and osteopenia. The physician suspects a collagen defect and orders a skin biopsy. The results of the biopsy show unstable type I collagen that is due to a single-point mutation in one of the type I genes. This mutation is most likely caused by which of the following amino acid substitutions in this patient?

A) Ala → Asp
B) Glu → Gln
C) Gly → Leu
D) Tyr → Trp
E) Ser → Phe

Question 18

A 28-year-old man sees his physician on a regular basis because he has suffered from bronchiectasis, chronic sinusitis, rhinitis, and secretory otitis media since childhood. He is currently being evaluated for infertility because he and his wife have been unable to conceive. His wife has been evaluated, and no abnormalities were found. The volume of his ejaculate and his sperm count are within reference ranges. Given his history and current findings, his infertility could best be explained by defective or absent production of which of the following cell structures?

A) Golgi complex
B) microtubules
C) mitochondria
D) peroxisomes
E) ribosomes

Question 19

Which of the following best describes how mitochondria reach the presynaptic endings of nerve cells?

A) ameboid migration down the axon from the neuronal cell body
B) assembly within the presynaptic ending from cytoplasmic lipids, amino acids, and other small molecules
C) assembly within the presynaptic ending using recycled presynaptic membranes
D) diffusion down the axon from the neuronal cell body
E) transport down the axon from the neuronal cell body along the microtubules

Question 20

You are studying the activity of isolated anterior
Pituitary cells in culture. Specifically you are interested in the function of microtubules in these cells.
Your studies involve the actions of the drug colchicine, which is a known inhibitor of microtubules
Function. Addition of colchicine to the culture
Medium will most likely result in which of the following in these pituitary cells?

A) induction of pseudopodia
B) inhibition of adenylate cyclase
C) inhibition of hormone secretion
D) stimulation of Ca²⁺ transport
E) stimulation of Na⁺ - K⁺ transport

Question 21

The movement and placement of organelles within animal cells is controlled by 2 ATP-binding motor
Proteins called kinesin and dynein. Mutations in either of these 2 proteins that interfere with these processes would most likely be associated with defective binding to which of the following structures?

A) actin filaments
B) ciliary doublets
C) intermediate filaments
D) microtubules
E) myosin fibrils

Question 22

An insoluble form of a prion protein accumulates
In the brains of patients who have CreutzfeldtJakob disease, CJD. Conversion of the normal
Soluble form of the prion protein to the pathologic
Insoluble form is thought to involve conversion
Of α-helices to β-pleated sheets. In order for this
Structural transition to occur, which of the following is most likely disrupted and reformed?

A) disulfide bonds
B) hydrogen bonds
C) peptide bonds
D) salt bridges
E) zinc fingers

Question 23

Eukaryotic ribosomes consist of 2 subunits designated as 40S and 60S. The S value is most dependent on which of the following properties of the subunit?

A) composition of the RNA bases
B) interactions between the RNA and protein components
C) protein content
D) RNA content
E) shape and size of the subunit