Deck 16: Proteins: Structure and Function

Question 1

This is a regular folding pattern in localized regions of the polypeptide backbone.

A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) both secondary and tertiary structures

Answer 1

secondary structure

Question 2

At low pH, the amino acid zwitterion reacts with hydronium (H₃O⁺).What is the product of this acid-base reaction?

A) structure a
B) structure b
C) structure c
D) structure d
E) structure e

Answer 2

structure d

Question 3

A protein's native conformation is

A) its shape when it is first made.
B) its shape when it is not bound to a substrate.
C) its three-dimensional shape in which it is biologically active.
D) the shape of the protein without any cofactors.
E) the amino acid sequence.

Answer 3

its three-dimensional shape in which it is biologically active.

Question 4

Amino acids that are not synthesized in the body and must be obtained from the diet are called

A) nonpolar.
B) incomplete.
C) necessary.
D) essential.
E) edible.

Question 5

Which side chain would MOST likely be involved in hydrogen bonding?

A) -CH₂OH
B) -CH₂SH
C) -CH₂COOH
D) -CH₂CONH₂
E)

Question 6

The carbon with the asterisk next to it is called the

A) anomeric carbon.
B) alpha carbon.
C) beta carbon.
D) gamma carbon.
E) side-chain carbon.

Question 7

An amino acid zwitterion has

A) a net positive charge.
B) a net negative charge.
C) a net neutral charge.
D) any non-neutral charge.
E) Zwitterions can have any charge.

Question 8

Which statement BEST describes the function of an enzyme in the body?

A) An enzyme acts as a buffer.
B) An enzyme transports waste out of the blood.
C) An enzyme signals cellular events.
D) An enzyme catalyzes chemical reactions.
E) All of the above describe the function.

Question 9

The following compound is a(n)

A) amino acid.
B) dipeptide.
C) tripeptide.
D) polypeptide.
E) protein.

Question 10

A protein acts as a catalyst if its name ends with

A) -ase.
B) -ate.
C) -ine.
D) -ous.
E) -ite.

Question 11

An example of this type of protein is shown below.

A) keratin
B) keratin, elastin, and collagen
C) membrane proteins and globular proteins
D) globular proteins
E) membrane proteins

Question 12

The following amino acid is classified as polar neutral.Which of the following statements best describes why it is classified this way? I.Its side chain is not ionizable. II.It buffers a solution at pH 7.
III)It is unreactive.
IV)Its side chain contains a polar functional group.

A) II only
B) III only
C) III and IV
D) I and IV
E) I and II

Question 13

How is the following amino acid classified?

A) nonpolar
B) polar neutral
C) polar acidic
D) polar basic
E) None of the above is a correct classification.

Question 14

The following amino acid is classified as nonpolar.Which statement BEST describes why it is classified this way?

A) It does not form a zwitterion.
B) It is neutral at physiological pH.
C) Its side chain is not charged at physiological pH.
D) Its side chain is a hydrocarbon.
E) This amino acid is soluble only in nonpolar solvents.

Question 15

During acidosis of a protein, shown below, salt bridges are broken, resulting in denaturation.Which choice shows the products of acidosis?

A)
B)
C)
D)
E)

Question 16

Which of the following are methods of denaturing a protein?

A) pH changes
B) heating
C) mechanical agitation
D) detergents
E) All of the above are methods.

Question 17

Physiological pH is a pH of approximately

A) 5.7.
B) 7.4.
C) 8.1.
D) 9.1.
E) 0.

Question 18

Hemoglobin contains iron.The iron is an example of a(n)

A) cofactor.
B) heme.
C) enzyme.
D) coenzyme.
E) metal.

Question 19

Sickle-cell anemia is caused by

A) an abnormal form of acetylcholine.
B) an abnormal form of iron.
C) too little iron.
D) an abnormal form of hemoglobin.
E) Actually, the cause of this disease is unknown.

Question 20

The following is a description of an enzyme called superoxide dismutase.Refer to this paragraph to answer the following question. Superoxide dismutase is an enzyme that detoxifies a free radical called superoxide.This radical is responsible for causing injury during reperfusion after a heart attack, and is also thought to play a role in Parkinson's Disease.^a Depending on what organism the protein is found in, it occurs either as a dimer or tetramer of identical subunits.^b The subunits are mostly α-helical with some β-sheet near the C-terminus.^c A metal binding site for manganese, iron, nickel or copper/zinc is composed of residues from both the N-terminus and the C-terminus.^d These residues are: His-26, His-81, Asp-167, His-171.^e
Which statement refers to a prosthetic group?

A) statement a
B) statement b
C) statement c
D) statement d
E) statement e

Question 21

Which choice shows how an amino acid reacts in a low pH solution?

A) choice a
B) choice b
C) choice c
D) choice d
E) All of these reactions occur to the same extent in a solution with a pH less than 7.

Question 22

How is the following amino acid classified?

A) nonpolar
B) polar neutral
C) polar acidic
D) polar basic
E) None of the above is a correct classification.

Question 23

This is the three-dimensional structure that occurs from electrostatic interaction between side chains.

A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) both secondary and tertiary structures

Question 24

A protein's primary structure is

A) its shape when it is first made.
B) its shape when it is not bound to a substrate.
C) its three-dimensional shape in which it is biologically active.
D) the shape of the protein without any cofactors.
E) its amino acid sequence.

Question 25

What types of biomolecules are enzymes?

A) only proteins
B) only DNA molecules
C) proteins and some carbohydrates
D) proteins and some RNA molecules
E) carbohydrates and some RNA molecules

Question 26

Which statement about noncompetitive inhibitors is FALSE?

A) Noncompetitive inhibitors are sometimes involved in feedback inhibition.
B) Noncompetitive inhibitors can serve a regulatory role in the body.
C) Noncompetitive inhibitors do not bind to the active site of an enzyme.
D) Increasing the concentration of a substrate restores function of an enzyme in the presence of a noncompetitive inhibitor.
E) Binding of a noncompetitive inhibitor results in deformation of an enzyme's active site.

Question 27

Which of the following is the proper amino acid chain designator of the peptide below? I.Val-Ser-Ala II.Ser-Ala-Val
III)Ala-Ser-Val

A) All of these represent the same molecule.
B) I and III
C) I only
D) II only
E) III only

Question 28

What type of secondary structure is in blue in the following protein?

A) an α-helix
B) a parallel β-pleated sheet
C) an antiparallel β-pleated sheet
D) a random coil
E) This illustration does not show secondary structure.

Question 29

Which amino acid side chain is capable of hydrogen?

A) -CH₃
B) -CH₂OH
C) -COOH
D) -CH₂CH₂SCH₃
E) All of the above are capable.

Question 30

What type of interaction would you expect between the following -R groups in the tertiary structure of a protein?

A) hydrogen bonds
B) hydrophobic interactions
C) peptide bonds
D) disulfide bonds
E) salt bridges

Question 31

Which structure illustrates an amino acid at physiological pH?

A) structure a
B) structure b
C) structure c
D) structure d
E) structure e

Question 32

The following table lists several common vegetarian foods and the amino acids that they are missing.Which of the following combinations supply a complete protein when consumed together? ​
Food
Missing amino acid(s)
Beans
Methionine and tryptophan
Corn
Lysine and tryptophan
Peas
Methionine
Rice
Lysine
Walnuts
Lysine and tryptophan
Wheat
Lysine
​

A) wheat and corn
B) corn and beans
C) beans and peas
D) peas and corn
E) beans and walnuts

Question 33

Which biomolecule has the MOST diverse functions in the body?

A) carbohydrates
B) proteins
C) nucleic acids
D) lipids
E) These have equally diverse functions.

Question 34

Enzymes are typically composed of this type of protein.

A) keratin
B) keratin, elastin, and collagen
C) membrane proteins and globular proteins
D) globular proteins
E) membrane proteins

Question 35

Which level of architecture is not affected by denaturation?

A) primary
B) secondary
C) tertiary
D) quaternary
E) All levels of architecture are affected by denaturation.

Question 36

How does the potential energy of a correctly folded protein compare to the energy of an unfolded protein or an incorrectly folded one?

A) The energy of a correctly folded protein is lower.
B) The energy of a correctly folded protein is higher.
C) The energy of proteins is the same no matter how they are folded or unfolded.
D) Proteins do not have energy.
E) Sometimes the energy of a correctly folded protein is lower, and sometimes it is higher.

Question 37

Is Gly-Ala-His the same tripeptide as His-Ala-Gly?

A) No, they are constitutional isomers.
B) No, they are stereoisomers.
C) Yes, they are conformers.
D) Yes, they are the same molecule, just flipped over.
E) Yes, the written order of amino acids does not make a difference in the peptide.

Question 38

Which side chain would MOST likely be found in the interior of a protein, away from the aqueous environment?

A) -CH₂OH
B) -CH₂SH
C) -CH₂COOH
D) -CH₂CONH₂
E)

Question 39

These proteins are structural in nature.

A) keratin
B) keratin, elastin, and collagen
C) membrane proteins and globular proteins
D) globular proteins
E) membrane proteins

Question 40

Aspartic acid has a side chain that contains a carboxylic acid.At physiological pH, what is the structure of aspartic acid?

A) structure a
B) structure b
C) structure c
D) structure d
E) structure e

Question 41

According to the following graph, the activity of the enzyme decreases more sharply at high temperature than at low temperature.What are the reasons for this observation? I.As temperature is increased, the substrate binding slowly becomes poorer. II.As temperature is decreased, the enzyme moves more slowly and so reacts more slowly.
III)At higher temperatures, the enzyme is denatured and stops working entirely.
IV)Temperature has no effect on enzyme activity.

A) I only
B) IV only
C) I and III
D) II and III
E) All are correct.

Question 42

Which statement BEST describes how an enzyme lowers the activation energy of a reaction?

A) The enzyme covalently binds to the substrate, lowering its energy.
B) The enzyme chemically reacts with the substrate to make it more reactive.
C) The enzyme increases the temperature of the substrate, making it more reactive.
D) The substrate is held in the correct orientation for the reaction to occur.
E) All of the above describe how an enzyme lowers the activation energy.

Question 43

Tamoxifen is a drug used to prevent the recurrence of certain types of breast cancers that require estrogen to grow.Tamoxifen binds to the active site of the estrogen receptor protein, preventing estrogen from binding to the enzyme.Once Tamoxifen binds to the protein, the protein is permanently deactivated.Which descriptions BEST fits Tamoxifen?

A) Tamoxifen is an irreversible, noncompetitive inhibitor.
B) Tamoxifen is a reversible, noncompetitive inhibitor.
C) Tamoxifen is an irreversible, competitive inhibitor.
D) Tamoxifen is a reversible, competitive inhibitor.
E) Tamoxifen is not an inhibitor.

Question 44

According to the graph below, which of the following is TRUE?

A) At high temperature, the activity of the enzyme decreases more sharply than it does at low temperature.
B) At low temperature, the activity of the enzyme decreases more sharply than it does at high temperature.
C) The maximum activity is at the lowest temperature.
D) The maximum activity is at the highest temperature.
E) The activity of the enzyme is the same at all temperatures.

Question 45

Hydrolysis of the peptide bonds in peptide below would result in

A) no reaction.
B) a single amino acid.
C) two amino acids.
D) three amino acids.
E) four amino acids.

Question 46

What is the relationship between the following two molecules?

A) They are enantiomers.
B) They are identical.
C) They are conformers.
D) They are constitutional isomers.
E) They are unrelated.

Question 47

The structure of myoglobin is shown below.Which level of architecture does this protein lack?

A) This protein has all levels of architecture.
B) primary
C) secondary
D) tertiary
E) quaternary

Question 48

The following is a description of an enzyme called superoxide dismutase.Refer to this paragraph to answer the following question. Superoxide dismutase is an enzyme that detoxifies a free radical called superoxide.This radical is responsible for causing injury during reperfusion after a heart attack, and is also thought to play a role in Parkinson's Disease.^a Depending on what organism the protein is found in, it occurs either as a dimer or tetramer of identical subunits.^b The subunits are mostly α-helical with some β-sheet near the C-terminus.^c A metal binding site for manganese, iron, nickel or copper/zinc is composed of residues from both the N-terminus and the C-terminus.^d These residues are: His-26, His-81, Asp-167, His-171.^e
Which statement refers to quaternary structure?

A) statement a
B) statement b
C) statement c
D) statement d
E) statement e

Question 49

What is the molecular shape of the carbon with the asterisk next to it?

A) linear
B) bent
C) trigonal planar
D) tetrahedral
E) pyramidal

Question 50

The amino acid sequence is the ________ of a protein.

A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) both secondary and tertiary structures

Question 51

Alpha-helices and β-pleated sheets are both examples of

A) primary structure.
B) secondary structure.
C) tertiary structure.
D) quaternary structure.
E) both secondary and tertiary structure.

Question 52

Which choice has the BEST labels for this amino acid?

A) 1: amino acid 2: carbon 3: side chain 4: alcohol
B) 1: amide 2: α-carbon 3: R 4.ester
C) 1: amine 2: side chain 3: α-carbon 4.ester
D) 1: amide 2: α-carbon 3: side chain 4.carbonyl
E) 1: amine 2: α-carbon 3: side chain 4.carboxylic acid

Question 53

Which structure is the enantiomer of L-alanine?

A) structure a
B) structure b
C) structure c
D) structure d
E) structure e

Question 54

What is indicated by the arrow pointing to part of the Fischer projection below?

A) Nothing, this is just two molecules with their bonds crossed.
B) This is a carbon in the side chain of an amino acid.
C) This is the alpha carbon of an amino acid.
D) This is a carbon with a planar geometry.
E) This can be any type of atom.

Question 55

Which statement about fibrous proteins is TRUE?

A) Fibrous proteins are soluble in water.
B) Fibrous proteins usually contain both β sheets and α-helices.
C) Fibrous proteins are the most common structural protein in the body.
D) Fibrous proteins are always rigid.
E) Hemoglobin is an example of a fibrous protein.

Question 56

Which of the following correctly shows the electrostatic interaction between amino acids that holds an α-helix or β-pleated sheet together?

A) -CH₂S-SCH₂-
B)
C)
D)
E) Any of these can act as the electrostatic interaction.

Question 57

Which of the amino acids does NOT contain a chiral carbon?

A) amino acid a
B) amino acid b
C) amino acid c
D) amino acid d
E) amino acid e

Question 58

Which statement about secondary structures is FALSE?

A) Some proteins only contain α-helices or β sheets.
B) Structural proteins often contain only β sheets.
C) Secondary structure is stabilized by hydrogen bonding between amides in the polypeptide backbone.
D) Side chains are involved in the hydrogen bonds that stabilize the secondary structure.
E) A protein can contain both α-helices and β sheets.

Question 59

Which structure illustrates an amino acid as a zwitterion?

A) structure a
B) structure b
C) structure c
D) structure d
E) structure e

Question 60

Is the peptide shown below chiral?

A) No, molecules with multiple chiral centers are not chiral.
B) Yes, it has chiral centers.
C) No, it has no chiral centers.
D) Yes, it has no chiral centers.
E) It is not possible to determine whether or not the peptide is chiral.

Question 61

What kinds of interactions are NOT part of tertiary protein structure?

A) hydrophobic interactions
B) peptide bonds
C) hydrophilic interactions
D) salt bridges
E) disulfide bonds

Question 62

Which statement BEST defines an essential amino acid?

A) It is an amino acid that is necessary for life.
B) It is an amino acid that is synthesized in the body.
C) It is any of the 20 amino acids.
D) It is another name for the nonpolar amino acids.
E) It is an amino acid that cannot be produced by the body.

Question 63

When several amino acids are connected together, head-to-tail, the resulting molecule is called a(n)__________.When more than 50 amino acids are connected together, the molecule is called a(n)___________.

A) enzyme; polypeptide
B) protein; polypeptide
C) polypeptide; protein
D) polypeptide; enzyme
E) nucleic acid; enzyme

Question 64

The most common motifs for this level of structure are the helix and the β- pleated sheet.

A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) both secondary and tertiary structures

Question 65

Prion disease is a disease of the ________________ protein structure.

A) primary
B) secondary
C) tertiary
D) quaternary
E) Prion disease does not involve proteins.

Question 66

In the peptide Ser-Gly-Asp-Ala, the N-terminal amino acid is

A) aspartic acid.
B) alanine.
C) cysteine.
D) serine.
E) glycine.

Question 67

Select the statement that BEST describes a key difference between competitive and noncompetitive inhibitors.

A) A competitive inhibitor binds to the active site, and a noncompetitive inhibitor does not.
B) A noncompetitive inhibitor binds to the active site, and a competitive inhibitor does not.
C) A competitive inhibitor is more effective than a noncompetitive inhibitor.
D) A noncompetitive inhibitor is more effective than a competitive inhibitor.
E) A noncompetitive inhibitor has structural similarities to the enzyme's active site, and the competitive inhibitor does not.

Question 68

Which statement about enzyme names is FALSE?

A) Enzymes are often named after the type of reaction that they catalyze or their substrate.
B) Enzyme names almost always include the name of any cofactors involved in their reaction.
C) Enzyme names often have -ase at the end of them.
D) Some enzymes are named after where they were isolated from.
E) Enzyme names are typically italicized.

Question 69

How does your body know which proteins to make and in what order to place the amino acids when the proteins are synthesized?

A) The body does not make proteins; they are consumed in the diet.
B) There are special proteins in which this information is encoded.
C) Our DNA acts as a blueprint for proteins.
D) Our brain does this subconsciously.
E) The answer is not known to science.

Question 70

The pH for optimum activity for most enzymes is

A) 5.4.
B) 7.4.
C) 8.0.
D) 9.0.
E) 10.4.

Question 71

Which of the following is NOT common to all peptides?

A) the peptide backbone
B) amide functional groups
C) peptide bonds
D) repeating N C_α
C=O units
E) an alanine N-terminus

Question 72

Which type of protein defends the body against infectious agents?

A) receptors
B) structural proteins
C) immunoglobulins
D) transport proteins
E) dietary proteins

Question 73

Not all proteins have this level of protein architecture.

A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) both secondary and tertiary structures

Question 74

Which of the following amino acids can form a disulfide bridge?

A) serine
B) alanine
C) cysteine
D) aspartic acid
E) lysine

Question 75

Which statement BEST describes the strategy used for treating hypertension through drug therapies?

A) to suppress how the body detects sodium
B) to suppress how the body detects low blood pressure
C) to lower blood pressure directly
D) to permanently disable renin
E) to inhibit the pathway that the body uses to increase blood pressure

Question 76

At physiological pH, most carboxylic acids exist in their conjugate base form.Which structure illustrates the conjugate base of a carboxylic acid?

A) HCOOH
B) CH₃COO⁺
C) HCOO⁺
D) HCOO^-
E) CH₃COOH₂⁺

Question 77

Which amino acid is polar neutral?

A) amino acid a
B) amino acid b
C) amino acid c
D) amino acid d
E) amino acid e

Question 78

The following is a description of an enzyme called superoxide dismutase.Refer to this paragraph to answer the following question. Superoxide dismutase is an enzyme that detoxifies a free radical called superoxide.This radical is responsible for causing injury during reperfusion after a heart attack, and is also thought to play a role in Parkinson's Disease.^a Depending on what organism the protein is found in, it occurs either as a dimer or tetramer of identical subunits.^b The subunits are mostly α-helical with some β-sheet near the C-terminus.^c A metal binding site for manganese, iron, nickel or copper/zinc is composed of residues from both the N-terminus and the C-terminus.^d These residues are: His-26, His-81, Asp-167, His-171.^e
Which statement refers to primary structure?

A) statement a
B) statement b
C) statement c
D) statement d
E) statement e

Question 79

The boxed bond in the following peptide is a

A) peptide bond.
B) ionic bond.
C) nonpolar covalent bond.
D) hydrogen bond.
E) chiral carbon.

Question 80

Which of the following is a complete protein?

A) meat
B) milk
C) eggs
D) soy
E) All of these are complete proteins.