Deck 21: Amino Acids,proteins,and Enzymes

Question 1

What is the three-letter abbreviation of asparagine?

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

Answer 1

Asn

Question 2

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

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

Answer 2

2

Question 3

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

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

Answer 3

6

Question 4

Which protein stores O₂ in tissues?

A)Keratin
B)Ferritin
C)Hemoglobin
D)Myoglobin

Question 5

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

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

Question 6

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 7

Which protein stores iron in the liver?

A)Ferritin
B)Keratin
C)Myoglobin
D)Collagen

Question 8

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

A)Alanine
B)Glycine
C)Methionine
D)Isoleucine

Question 9

What is the structure of the dipeptide Ser-Gly?

A)
B)
C)
D)

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 is the simplest amino acid?

A)Serine
B)Glutamine
C)Cysteine
D)Glycine

Question 12

What is the one-letter abbreviation of arginine?

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

Question 13

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 14

Which amino acid is a basic amino acid?

A)Serine
B)Arginine
C)Cysteine
D)Alanine

Question 15

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

A)Alanine
B)Glycine
C)Methionine
D)Isoleucine

Question 16

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

A)
B)
C)
D)

Question 17

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 18

What is the name of the amino acid shown below?

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

Question 19

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

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

Question 20

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 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.

Question 22

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 23

Which is an example of a cofactor?

A)Lactose
B)Lactose dehydrogenase
C)NAD⁺ (nicotinamide adenine dinucleotide)
D)Tryptophan

Question 24

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.

Question 25

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 26

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 27

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

Question 28

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.

Question 29

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 30

Which choice is the unique structural feature of collagen?

A)α-coil
B)β-sheet
C)Disulfide linkage
D)Triple helix

Question 31

Which is an example of a globular protein?

A)Collagen
B)α-keratin
C)Hemoglobin
D)Amylopectin

Question 32

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 33

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

A)Glycine
B)Valine
C)Tyrosine
D)Alanine

Question 34

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

A)
B)
C)
D)

Question 35

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 36

Based on its name,which compound is an enzyme?

A)Glucose
B)Triosephosphate isomerase
C)N-acetyl-D-glucosamine
D)Dihydrofolate

Question 37

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 38

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 39

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 40

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 41

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 42

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 43

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 44

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

Question 45

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

Question 46

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

A)Methionine
B)Serine
C)Arginine
D)Cysteine

Question 47

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

Question 48

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.

Question 49

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

A)High temperature
B)Low temperature
C)Strong acid
D)Agitation

Question 50

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

Question 51

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)

Question 52

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 53

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

Question 54

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

Question 55

The Fischer projection below represents a naturally occurring amino acid.

Question 56

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

Question 57

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

Question 58

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

Question 59

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 60

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

Question 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.

Question 62

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

Question 63

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

Question 64

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

Question 65

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

Question 66

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

Question 67

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

Question 68

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

Question 69

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

Question 70

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

Question 71

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

Question 72

The Fischer projection below represents a basic amino acid.

Question 73

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

Question 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.

Question 75

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

Question 76

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

Question 77

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

Question 78

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

Question 79

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

Question 80

The peptide leucyl phenylalanylvalylvaline is abbreviated as Leu-Phen-Ala-Val-Val.