Deck 21: Amino Acids, Proteins, and Enzymes

Question 1

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

A)3
B)4
C)5
D)9

Answer 1

A

Question 2

The term protein is usually reserved for polymers of more than _____ amino acids.

A)10
B)40
C)200
D)1000

Answer 2

B

Question 3

Which amino acid is a basic amino acid?

A)serine
B)arginine
C)cysteine
D)alanine

Answer 3

B

Question 4

Which is the simplest amino acid?

A)serine
B)glutamine
C)cysteine
D)glycine

Question 5

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

A)alanine
B)glycine
C)methionine
D)isoleucine

Question 6

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

A)3
B)6
C)18
D)27

Question 7

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.

Question 8

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

A)1
B)2
C)3
D)4

Question 9

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

Question 10

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

Question 11

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.

Question 12

Which protein stores iron in the liver?

A)ferritin
B)keratin
C)myoglobin
D)collagen

Question 13

What is the one-letter abbreviation of arginine?

A)A
B)R
C)P
D)G

Question 14

What is the three-letter abbreviation of asparagine?

A)Asp
B)Asg
C)Asn
D)Arg

Question 15

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.

Question 16

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

A)alanine
B)glycine
C)methionine
D)isoleucine

Question 17

What is the name of the amino acid shown below?

A)L-cysteine
B)D-cysteine
C)L-serine
D)D-serine

Question 18

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.

Question 19

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

Question 20

Which protein stores O₂ in tissues?

A)keratin
B)ferritin
C)hemoglobin
D)myoglobin

Question 21

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.

Question 22

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

Question 23

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

A)glycine
B)valine
C)tyrosine
D)alanine

Question 24

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

Question 25

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

Question 26

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.

Question 27

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

Question 28

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.

Question 29

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.

Question 30

Based on its name, which compound is an enzyme?

A)glucose
B)triosephosphate isomerase
C)N-acetyl-D-glucosamine
D)dihydrofolate

Question 31

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

Question 32

Which is not a characteristic of an $\alpha$ -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.

Question 33

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

Question 34

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.

Question 35

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.

Question 36

Which is an example of a globular protein?

A)collagen
B) $\alpha$ -keratin
C)hemoglobin
D)amylopectin

Question 37

Which is an example of a cofactor?

A)lactose
B)lactose dehydrogenase
C)NAD⁺ (nicotinamide adenine dinucleotide)
D)tryptophan

Question 38

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

Question 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.

Question 40

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.

Question 41

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

Question 42

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

Question 43

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

Question 44

Both the myosin and the $\alpha$ -keratin are proteins composed almost entirely of $\beta$ -pleated sheets.

Question 45

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

Question 46

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

Question 47

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

Question 48

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

Question 49

The $\beta$ -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.

Question 50

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

Question 51

The $\alpha$ -helix and the $\beta$ -pleated sheet are examples of the tertiary structure of a protein.

Question 52

The Fischer projection below represents a basic amino acid.

Question 53

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

Question 54

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

Question 55

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.

Question 56

The Fischer projection below represents a naturally occurring amino acid.

Question 57

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

Question 58

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

Question 59

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

Question 60

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

Question 61

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

Question 62

The peptide leucylphenylalanylvalylvaline is abbreviated as Leu-Phen-Ala-Val-Val.

Question 63

There are _____ amino acids that occur naturally in proteins.

Question 64

$\alpha$ -Keratin in hair is a fibrous protein composed almost exclusively of $\alpha$ -helix units that wind together to form a superhelix.

Question 65

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

Question 66

All amino acids have at least one chirality center.

Question 67

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

Question 68

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

Question 69

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

Question 70

The $\beta$ -pleated sheet arrangement of a protein is favored by amino acids with small side chains.

Question 71

The enzyme in the ribbon diagram shown is composed primarily of $\beta$ -pleated sheets.

Question 72

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

Question 73

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.

Question 74

Zwitterions have low melting points and are water soluble.

Question 75

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

Question 76

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

Question 77

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

Question 78

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

Question 79

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

Question 80

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