Test Bank Chapter 21 Amino Acids, Proteins, and Enzymes

General, Organic and Biological Chemistry, 4e (Smith)

Chapter 21 Amino Acids, Proteins, and Enzymes

1) Which protein stores iron in the liver?

A) Ferritin

B) Keratin

C) Myoglobin

D) Collagen

2) Which protein stores O2 in tissues?

A) Keratin

B) Ferritin

C) Hemoglobin

D) Myoglobin

3) What is the function of myosin in the human body?

A) As connective tissue found in tendons, bone, cartilage, and blood vessels

B) Control muscle contractions

C) Stores iron in the liver

D) Controls blood glucose levels

4) Which is the simplest amino acid?

A) Serine

B) Glutamine

C) Cysteine

D) Glycine

5) Which amino acid is a basic amino acid?

A) Serine

B) Arginine

C) Cysteine

D) Alanine

6) Which Fischer projections represent naturally-occurring amino acids?

A) Only structure 1

B) Only structure 2

C) Structures 1, 2, and 3

D) Structures 2 and 3

7) What is the name of the amino acid shown below?

A) L-cysteine

B) D-cysteine

C) L-serine

D) D-serine

8) What is the three-letter abbreviation of asparagine?

A) Asp

B) Asg

C) Asn

D) Arg

9) What is the one-letter abbreviation of arginine?

A) A

B) R

C) P

D) G

10) What is the charge on a zwitterion?

A) Positive

B) Neutral

C) Negative

D) The charge or lack of charge varies depending on the amino acid.

11) What is the charge on an amino acid at a pH below its pI?

A) Positive

B) Neutral

C) Negative

D) The charge or lack of charge varies depending on the amino acid.

12) What is the structure of the amino acid leucine at pH 12?

A)

B)

C)

D)

13) The term protein is usually reserved for polymers of more than ________ amino acids.

A) 10

B) 40

C) 200

D) 1000

14) How is a dipeptide formed?

A) The –NH3+ group of one amino acid forms an amide bond with the –NH3+ group of another amino acid and the elements of H2 are removed.

B) The –NH3+ group of one amino acid forms an amide bond with the carboxylate (–COO–) of another amino acid, and the elements of H2O are removed.

C) The carboxylate (–COO–) group of one amino acid forms an amide bond with the carboxylate (–COO–) of another amino acid, and the elements of O2 are removed.

D) The carboxylate (–COO–) group of one amino acid forms an amide bond the –NH3+ group of another amino acid, and the elements of H2 are removed.

15) How many different dipeptides can be formed when one valine reacts with one glycine?

A) 1

B) 2

C) 3

D) 4

16) How many different tripeptides can be formed when one isoleucine, one alanine, and one glycine react?

A) 3

B) 6

C) 18

D) 27

17) What is the C-terminal amino acid in the tetrapeptide glycylalanyisoleucylmethionine?

A) Alanine

B) Glycine

C) Methionine

D) Isoleucine

18) What is the N-terminal amino acid in the tetrapeptide glycylalanyisoleucylmethionine?

A) Alanine

B) Glycine

C) Methionine

D) Isoleucine

19) What is the structure of the dipeptide Ser–Gly?

A)

B)

C)

D)

20) How many chirality centers are in leu-enkephalin (structure shown)?

A) 3

B) 4

C) 5

D) 9

21) Which statement about oxytocin and vasopressin is not true?

A) Oxytocin and vasopressin each contain nine amino acids.

B) Oxytocin and vasopressin each contain cysteine on both sides of a disulfide bond.

C) Oxytocin and vasopressin each contain a single disulfide bond.

D) Oxytocin and vasopressin each contain cysteine as the C-terminal amino acid.

22) What is the particular sequence of amino acids of a protein that are joined together by peptide bonds called?

A) The primary structure of a protein

B) The secondary structure of a protein

C) The tertiary structure of a protein

D) The quaternary structure of a protein

23) Which is not a characteristic of an α-helix?

A) The N–H and C=O bonds point along the axis of the helix in opposite directions.

B) The R groups of the amino acids extend inward toward the core of the helix.

C) There are 3.6 amino acids in each turn of the helix.

D) The C=O group of one amino acid is hydrogen bonded to an N–H group four amino acid residues farther along the chain.

24) Which choice is the unique structural feature of collagen?

A) α-coil

B) β-sheet

C) Disulfide linkage

D) Triple helix

25) What is the strongest type of interaction between two cysteine amino acid side chains in a protein?

A) Hydrogen bonding

B) London dispersion forces

C) Disulfide bond

D) Electrostatic interactions

26) What is the strongest type of interaction between the side chains of an isoleucine amino acid and a phenylalanine amino acid in a protein?

A) Hydrogen bonding

B) London dispersion forces

C) Disulfide bond

D) Electrostatic interactions

27) What is the process of altering the shape of a protein without breaking the amide bonds that form the primary structure?

A) Hydrolysis

B) Competitive inhibition

C) Denaturation

D) Oxidation

28) Which statement is not true?

A) A cofactor is always a metal ion needed for an enzyme-catalyzed reaction to occur.

B) The names of most enzymes end in the suffix -ase.

C) An enzyme-catalyzed reaction can be 106 to 1012 times faster than a similar uncatalyzed reaction.

D) Enzymes are proteins that serve as biological catalysts for reactions in all living organisms.

29) Based on its name, which compound is an enzyme?

A) Glucose

B) Triosephosphate isomerase

C) N-acetyl-D-glucosamine

D) Dihydrofolate

30) What type of inhibitor binds to the enzyme but does not bind at the active site?

A) A noncompetitive inhibitor

B) A competitive inhibitor

C) A reversible inhibitor

D) An irreversible inhibitor

31) A reversible inhibitor does which of the following?

A) It covalently binds to an enzyme, permanently destroying its activity.

B) It binds to the enzyme, but does not bind at the active side.

C) It binds to an enzyme but then enzyme activity is restored when the inhibitor is released.

D) It has a shape and structure similar to the substrate, so it competes with the substrate for binding to the active side.

32) What is a zymogen?

A) An amino acid with a neutral charge

B) Inactive precursor of an enzyme

C) A molecule that causes an enzyme to lose activity

D) A nonprotein organic molecule needed for an enzyme-catalyzed reaction to occur

33) Which conditions are commonly diagnosed by measuring the levels of specific enzymes in the blood?

A) Heart attack

B) High blood pressure

C) Pregnancy

D) Migraines

34) The side chain of which amino acid can form hydrogen bonds with asparagine?

A) Glycine

B) Valine

C) Tyrosine

D) Alanine

35) Trypsin is a digestive enzyme that hydrolyzes peptide bonds only when the carbonyl group in the amide bond comes from Lys or Arg. What fragments result when the peptide Gly-Lys-Arg-Ala-Ala-Arg is hydrolyzed by trypsin?

A) Gly, Lys, Arg, Ala-Ala, Arg

B) Gly-Lys, Arg-Ala-Ala, Arg

C) Gly-Lys, Arg, Ala-Ala, Arg

36) What is the structure of the amino acid phenylalanine at pH 1?

A)

B)

C)

D)

37) Which is an example of a globular protein?

A) Collagen

B) α-keratin

C) Hemoglobin

D) Amylopectin

38) Which is an example of a cofactor?

A) Lactose

B) Lactose dehydrogenase

C) NAD+ (nicotinamide adenine dinucleotide)

D) Tryptophan

39) Amino acids are the building blocks of the body's proteins. Which statement concerning amino acids is false?

A) There are approximately 200 standard amino acids that occur naturally in the proteins of the human body.

B) Except for when R=H, amino acids are chiral molecules.

C) The amino acids found in human proteins are "alpha" amino acids.

D) The properties of amino acids and the proteins they compose are determined by the nature of the side chain groups that are present.

40) What type of intermolecular forces exist between the side chains of isoleucine and valine?

A) Electrostatic attraction

B) London dispersion forces

C) Hydrogen bond

D) Disulfide bond

41) What type of intermolecular forces exist between the side chains of serine and asparagine?

A) Electrostatic attraction

B) London dispersion forces

C) Hydrogen bond

D) Disulfide bond

42) What type of intermolecular forces exist between the side chains of glutamic acid and lysine?

A) Electrostatic attraction

B) London dispersion forces

C) Hydrogen bond

D) Disulfide bond

43) Proteins are long chains of amino acids joined together by peptide bonds. Which structure properly depicts the peptide bond formed between two generic amino acids?

A)

B)

C)

D)

44) Which choice is the only amino acid capable of forming a disulfide bond?

A) Methionine

B) Serine

C) Arginine

D) Cysteine

45) Tuftsin is a peptide that stimulate and promotes the destruction of tumor cells. Its primary structure is Thr-Lys-Pro-Arg. Which statement is NOT a valid interpretation of its primary structure?

A) It is a tetrapeptide.

B) Threonine is the N-terminal amino acid and arginine is the C-terminal amino acid.

C) The amino group of arginine is not joined to any other amino acid.

D) The carboxyl group of lysine is joined to the amino group of proline.

46) Consider the following forms of the amino acid valine (Val). Which statement concerning these structures is false?

A) Structure I represents the form of Val present in blood at physiological pH.

B) Structure II represents the form of Val present in the basic environment of the intestines.

C) Structure III represents the form of Val present in the acidic environment of the stomach.

D) Structure IV represents the zwitterions of Val.

47) Consider the following forms of the amino acid serine (Ser). Which statement concerning these structures is false?

A) Structure IV represents the form of Ser present at its isoelectric pH.

B) Structure III represents the form of Ser present in the basic environment of the intestines.

C) Structure II represents the form of Ser present in the acidic environment of the stomach.

D) Structure I represents the zwitterionic form of Ser.

48) Denaturation of a protein results in the loss of its native conformation and its biological activity. Which statement best describes what happens to a protein when it is denatured?

A) Peptide bonds are broken.

B) New amino acids are joined to the peptide backbone.

C) Secondary, tertiary, and quaternary levels of structure are disrupted.

D) The N-terminal and C-terminal ends of the protein are hydrolyzed by enzymes.

49) Which of the following is not of the causes of protein denaturation?

A) High temperature

B) Low temperature

C) Strong acid

D) Agitation

50) About one half of the 223 amino acid residues in the enzyme trypsin are hydrophobic. Where in the tertiary structure of this globular protein are these residues most likely to be found?

A) At the N-terminal end of the peptide chain.

B) At the C-terminal end of the peptide chain.

C) On the exterior surface of the folded protein.

D) In the interior of the folded protein.

51) D-Amino acids have the –NH3+ group on the left side in the Fischer projection.

52) A diet of rice and tofu provides all essential amino acids.

53) The Fischer projection below represents a naturally occurring amino acid.

54) A dipeptide contains two amino acids joined together by two amide bonds.

55) The amide bonds in peptides and proteins are called peptide bonds.

56) By convention, the C-terminal amino acid is always written at the right end of the peptide chain and the N-terminal amino acid at the left.

57) The reactant in an enzyme-catalyzed reaction is called a cofactor.

58) Secretion of vasopressin by the pituitary gland causes the kidneys to retain fluid, resulting in decreased urine output.

59) The α-helix and the β-pleated sheet are examples of the tertiary structure of a protein.

60) Both the myosin and the α-keratin are proteins composed almost entirely of β-pleated sheets.

61) The β-pleated sheet forms when two or more peptide chains, called strands, line up side-by-side with the C=O and N–H bonds in the plane of the sheets.

62) Insulin is a small protein consisting of two polypeptide chains held together by hydrogen bonds.

63) Globular proteins are coiled into compact shapes with hydrophilic outer surfaces that make them water-soluble.

64) Hemoglobin, collagen, and myoglobin are all examples of conjugated proteins.

65) The hydrolysis of the amide bonds in a protein forms the individual amino acids that comprise the primary structure.

66) The lock-and-key model is often used to explain why some enzymes catalyze a wide variety of substrate reactions.

67) The antibiotics penicillin and sulfanilamide, and drugs used to treat high blood pressure and acquired immune deficiency syndrome (AIDS) are classified as coenzymes.

68) When the peptide below is hydrolyzed with water, the products are the amino acids proline, cysteine, and glutamine.

69) The Fischer projection below represents a basic amino acid.

70) Acidic amino acids have lower pI values than basic amino acids.

71) Serine exists primarily in its neutral form at a pH ~ 6.

72) The peptide leucyl phenylalanylvalylvaline is abbreviated as Leu–Phen–Ala–Val–Val.

73) Hydrogen bonding is possible between the side chains of the amino acids tyrosine and threonine.

74) The amino acids aspartic acid and glutamic acid have a +1 net charge at low pH, and a –2 net charge at high pH.

75) HIV protease inhibitors are used to treat HIV by binding to an enzyme needed by the virus to replicate itself.

76) α-Keratin in hair is a fibrous protein composed almost exclusively of α-helix units that wind together to form a superhelix.

77) Fibrin and thrombin, two proteins involved in blood clotting, are first synthesized as the zymogens fibrinogen and prothrombin, respectively.

78) The enzyme in the ribbon diagram shown is composed primarily of β-pleated sheets.

79) The "cartoon" shown is an example of competitive inhibition.

80) The "cartoon" shown is an example of noncompetitive inhibition.

81) It is possible for two different proteins to contain the same number and type of amino acids.

82) The β-pleated sheet arrangement of a protein is favored by amino acids with small side chains.

83) In hydrolysis of a peptide or protein, the addition of water breaks the hydrogen bonds that hold the amino acids together in the peptide chain.

84) Amino acids with an additional COOH group in the side chain are classified as acidic amino acids.

85) Amino acids typically exist in nature as neutral molecules with all uncharged atoms.

86) Zwitterions have low melting points and are water-soluble.

87) Humans can synthesize only twenty of the amino acids needed for proteins.

88) No one plant source has sufficient amounts of all of the essential amino acids.

89) All amino acids have at least one chirality center.

90) There are ________ amino acids that occur naturally in proteins.

A) 12

B) 15

C) 20

D) 21

E) 30

91) Since amino acids contain a base (NH2 group) and an acid (COOH), proton transfer from the acid to the base forms a salt called a/an ________, which contains both a positive and a negative charge.

92) The pH at which an amino acid exists primarily in its neutral form is called its ________ point.

93) Molecules that cause an enzyme to lose its activity are called ________.

94) ________ bonds between cysteine residues are the only covalent bonds that stabilize the tertiary structure of a protein.

95) ________ proteins are composed of long linear polypeptide chains that are bundled together to form rods or sheets that are insoluble in water and serve structural roles.

96) The difference between normal hemoglobin and sickle cell hemoglobin is that a single amino acid of both β subunits is changed from glutamic acid to ________.

97) The ________ of an enzyme is the region where substrate binding and catalysis occur.

98) A ________ is a peptide that contains four amino acids joined together by three peptide bonds.