Deck 12: Peptides, Proteins, and Enzymes

Question 1

Which is an $\alpha$ -amino acid?

A)
B)
C)
D)

Answer 1

Question 2

At physiological pH, most amino acids carry both a 1+ and 1- charge. This form is known as a ___.

A) zwitterion
B) anion
C) cation
D) isoelectric ion

Answer 2

zwitterion

Question 3

Shown here is the amino acid glycine at a pH of ___.

A) 1
B) 7
C) 14
D) both 1 and 14

Answer 3

1

Question 4

Stereoisomers exist for most of the amino acids found in nature. Which statement below is correct?

A) Both the D-amino acids and the L- amino acids are used by living things.
B) Only the L-amino acids are incorporated in proteins.
C) A common conversion is from the D-amino acid to the L-amino acid.
D) L-amino acids are toxic.

Question 5

If an amino acid is in a neutral solution, the form the carboxyl group takes is ___.

A) -CO^2-
B) -CO₂H⁺
C) -CO₂^-
D) -CO₂H

Question 6

The side chain of the amino acid phenylalanine is shown here.
The side chain is classified as ___.

A) nonpolar
B) polar-acidic
C) polar-basic
D) polar-neutral

Question 7

The side chain of the amino acid tyrosine is shown here.
The side chain is classified as ___.

A) nonpolar
B) polar-acidic
C) polar-basic
D) polar-neutral

Question 8

The side chain of the amino acid histidine is shown here.
The side chain is classified as ___.

A) nonpolar
B) polar-acidic
C) polar-basic
D) polar-neutral

Question 9

The structure of the amino acid glutamine is shown below. Glutamine can be classified as

A) polar-neutral
B) polar -acidic
C) polar basic
D) nonpolar

Question 10

Shown here is the amino acid glycine at a pH of ___.

A) 1
B) 7
C) 14
D) both 1 and 14

Question 11

The structures of the amino acids proline and glycine are shown below. Which of the following statements is true?

A) glycine is an $\alpha$ -amino acid, but proline is not
B) both proline and glycine are chiral molecules
C) glycine is achiral and proline is chiral
D) proline exists as four enantiomers

Question 12

Shown here is the amino acid glycine at a pH of ___.

A) 1
B) 7
C) 14
D) both 1 and 14

Question 13

Aspartic acid is classified as a polar-acidic amino acid due to

A) the -CH group to which the amide group is attached.
B) the -CH₂ group in the middle of the side chain.
C) the amide group located on a side chain.
D) the carboxyl group located on the side chain.

Question 14

What form does isoleucine take at pH 14?

A)
B)
C)
D)

Question 15

The peptide bond that connects amino acids in proteins is actually an ___ linkage.

A) amine
B) amide
C) ether
D) ester

Question 16

The term commonly used for a chain of amino acids 100 units long is ___.

A) peptide
B) oligopeptide
C) polypeptide
D) centapeptide

Question 17

Which reaction is capable of breaking polypeptides into their component amino acids?

A) hydrogenation (adding hydrogen)
B) hydrolysis (adding water)
C) dehydrogenation (removing hydrogen)
D) dehydration (removing water)

Question 18

Leucine-enkephalin, a pentapeptide, is a naturally occurring pain reliever found in the brain. How many peptide bonds are there in leucine-enkephalin?

A) 5
B) 4
C) 6
D) 3

Question 19

A tetrapeptide is given as: Ser-Lys-Ala-Pro. Which of the following statements is true?

A) The serine provided a nitrogen for the peptide bond.
B) The N-terminus is serine (Ser).
C) There are four peptide bonds because there are four amino acids.
D) The listing should be in alphabetical order.

Question 20

The form of dipeptide aspatylserine (Asp-Ser) obtained from two amino acids, aspartic acid and serine, whose structures are shown here, is

A)
B)
C)
D)

Question 21

Where is the peptide bond located in this dipeptide?

A) the CO-NH joining serine and the valine
B) the doubly bonded oxygen just left of center between the amino acids
C) the CH-CO on the top of the serine going to the right
D) the NH-CH between the serine and valine

Question 22

What is the net charge on the oligopeptide in the figure shown here at pH 1?

A) 3+
B) 1+
C) 2+
D) 0

Question 23

The structure of the dipeptide, Phe-Gly, in a solution of pH 14 is ___.

A)
B)
C)
D)

Question 24

A biologically active protein referred to as a simple protein contains

A) very few hydrogen bonds.
B) only one heme group.
C) less than three different amino acids.
D) no prosthetic groups.

Question 25

The element found in the center of the heme prosthetic group is ___.

A) iron
B) sulfur
C) nitrogen
D) carbon

Question 26

Which interactions are involved in establishing and holding the three-dimensional structure of a protein?

A) salt bridge and disulfide bonds
B) hydrogen bonds
C) hydrophobic effects
D) all of these choices

Question 27

Proteins tend to assume a specific overall three-dimensional shape. This is referred to as the protein's ___.

A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure

Question 28

A contributing factor to the tertiary structure of a protein is a covalent bond between two atoms of ___.

A) sulfur
B) hydrogen
C) carbon
D) nitrogen

Question 29

Which of the following sentences is true?

A) Rearranging the amino acid residues in a peptide or protein changes its function.
B) In an $\alpha$ -helix form, portions of polypeptide chain line up side by side with hydrogen bonds holding neighboring strands of sheet together.
C) The order of amino acid residues in a protein is referred to as its tertiary structure.
D) The overall three-dimensional shape of a protein is referred to as its primary structure.

Question 30

The overall three-dimensional shape of a protein is determined by its ___ and is known as the ___ structure of a protein.

A) amino acid residues/primary
B) amino acid residues/tertiary
C) isoelectric point/secondary
D) hydrogen bonding/secondary

Question 31

Which of the following do not contribute to the overall stability of a tertiary structure of proteins?

A) salt bridges
B) hydrogen bonding
C) hydrophobic effect
D) hormones

Question 32

Globular proteins in water typically assume their specific shapes because

A) they are water-soluble due to the polar points located along the length of the protein molecules.
B) the nonpolar portion of the molecule is inside and the polar portion is outside, as stated by the folding rule.
C) they can assume the $\alpha$ -sheet form, which stretches along the surface of the solution.
D) all of the polar side chains in the molecular structure fold inward to be protected from the effects of the polarity of water.

Question 33

The hydrophobic portions of a protein tend to

A) form chemical bonds between them so that the structure of the protein is rigid.
B) be attracted to each other by means of strong interatomic forces.
C) be strongly attracted to the water in the surroundings, pulling portions of the molecule away from its center.
D) fold into the interior of the three-dimensional shape away from water.

Question 34

In which of the following levels of protein structure can hydrogen bonding NOT play a role?

A) primary
B) secondary
C) tertiary
D) quaternary

Question 35

Proteins can contain prosthetic groups, which are

A) polypeptide chains that contain only one kind of amino acid.
B) polypeptide chains that come off the main chain to form a branch.
C) groups containing nonpeptide components.
D) groups of amino acids that form accessory structures to the protein.

Question 36

What kind of noncovalent interaction occurs between the -NH₃⁺ ending of one side chain of an amino acid with the -COO^- ending of sidechain of another amino acid in tertiary structure of a protein?

A) salt bridge
B) hydrogen bonding
C) covalent disulfide bond
D) hydrophobic effect

Question 37

Which of the following substances recognized by immune system evoke production of one or more antibodies?

A) secondary proteins
B) antigens
C) globular proteins
D) glycolipids

Question 38

Which is a means of denaturing a protein?

A) changes in temperature
B) changes in pH
C) use of detergents or soaps
D) all of these choices

Question 39

The ___ is the location on the protein molecule where enzyme catalyzed reactions take place.

A) substrate
B) zymogen
C) active site
D) coenzyme

Question 40

An enzyme displays ___ when the enzyme accepts only one specific substrate.

A) absolute specificity
B) relative specificity
C) stereospecificity
D) no specificity

Question 41

Catalysts, including enzymes, have the role of

A) changing a nonspontaneous chemical reaction to spontaneous.
B) lowering the activation energy of a reaction.
C) heating up the reactants to make the reaction progress faster.
D) changing the pH to a favorable pH for the reaction to progress.

Question 42

The enzyme known as alcohol dehydrogenase is capable of oxidizing ethanol, methanol and other hydroxyl group containing organic compounds into their corresponding aldehydes. Such an enzyme with ___ catalyzes the reaction of structurally related substances.

A) absolute specificity
B) relative specificity
C) stereospecificity
D) no specificity

Question 43

Organic compounds that are not polypeptides but are necessary for enzymes to properly function are called ___.

A) substrates
B) zymogens
C) active sites
D) coenzymes

Question 44

A change in pH usually produces a change in enzyme activity because

A) pH of the environment changes the conformation of the enzyme.
B) enzyme activity increases at extreme pH values (either acidic or basic).
C) enzyme activity is usually least active below its optimum pH.
D) enzyme activity is most active above its optimum temperature.

Question 45

Many of the chemical reactions of living things involve enzymes, which are

A) proteins that are in the form of parallel sheets.
B) proteins that catalyze reactions.
C) small DNA molecules.
D) denatured proteins.

Question 46

A certain enzyme's name is glucose-6-phosphorylase. This enzyme most likely catalyzes a reaction that

A) converts glucose into six phosphorous atoms.
B) synthesizes six glucose molecules.
C) joins six glucose molecules to a phosphate.
D) places a phosphate on the sixth carbon of glucose.

Question 47

The enzyme hexokinase catalyzes the transfer of a phosphate group from ATP to carbon 6 of D-glucose and other D-hexoses. L-hexoses are not substrates to the enzyme.
Hexokinase displays

A) relative specificity
B) stereospecificity
C) absolute specificity
D) both relative specificity and stereospecificity

Question 48

___ are inactive enzyme precursors that are synthesized, stored and may be activated where needed.

A) Substrates
B) Zymogens
C) Active sites
D) Coenzymes

Question 49

An inhibitor is a substance that affects an enzyme by

A) reducing the ability to act as a catalyst.
B) removing the prosthetic group from an enzyme.
C) reacting with the enzyme so there is less effect of the chemical reaction's surroundings on the rate of reaction.
D) stopping the separation of the enzyme from the product keeping the reaction from going to completion.

Question 50

The function of feedback inhibition is to

A) affect the polarity of a substrate so that it will not be picked up by an enzyme.
B) provide a stimulus to the enzyme that makes it active during a reaction.
C) provide a way of keeping the wrong substrate from coming in contact with an enzyme.
D) control an enzyme reaction so that there isn't an overproduction of the product.

Question 51

An allosteric enzyme differs from a Michaelis-Menten enzyme because the allosteric enzyme

A) has a more active binding site that is more polar and will hold the substrate longer.
B) displays cooperativity in which the binding of a substrate to the active site on one subunit affects the binding of substrate at other subunits.
C) operates to change reaction rates of all of the stereoisomers of a compound, not just one.
D) will catalyze all the reactions of a substance produced in a series of steps.

Question 52

A characteristic of a Michaelis-Menten enzyme is that it

A) inhibits the formation of a complex under the reaction conditions.
B) forms an enzyme-substrate complex that is stable.
C) forms an enzyme-substrate complex after which the product and the enzyme separate.
D) is a system specific to the hydrolysis of complex carbohydrates.

Question 53

When a patient has accidentally ingested methanol, a physician can order the use of ethanol to overwhelm the alcohol dehydrogenase enzyme. This prevents the liver from producing deadly formaldehyde from the methanol. This is an example of _____.

A) covalent modification
B) feedback inhibition
C) competitive inhibition
D) protein denaturation

Question 54

Alanine is the only $\alpha$ -amino acid that does not have a chiral carbon.

Question 55

Because amino acids contain polar covalent bonds, they are hydrophilic and will dissolve water.

Question 56

The net charge of peptides and proteins affects their solubility.

Question 57

Hydrogen bonding plays a role in the primary structure of protein.

Question 58

Fibrous proteins, because of their long fibers, tend to be soluble in water.

Question 59

Protein molecules with the appropriate structure to be biologically active are native molecules.

Question 60

A characteristic that distinguishes between secondary and tertiary structures is the fact that hydrogen bonding in all secondary structures are between backbone -C=O and H-N- groups.

Question 61

Proteins can be denatured by changes in temperature or pH.

Question 62

Cofactors for some enzymes are not considered prosthetic groups because they are loosely held during the course of reaction.

Question 63

Enzymes that display stereospecificity are those that will catalyze the reactions of both the L-form and the D-form of a carbohydrate.

Question 64

Noncompetitive inhibitors resemble the substrate and bond to the active site of an enzyme.

Question 65

___ is the pH at which an amino acid solution has no net charge because it has equal positive and negative charges.

Question 66

___ are composed of more than 10 amino acid residues.

Question 67

The amide bond between two amino acids is referred to as a ___ bond.

Question 68

The oligopeptides have from 2 to ___ amino acid units in their molecules.

Question 69

As in α-helix, and the β-sheet are held together by ___ between amide-N-H and C=O groups.

Question 70

The ___ of a protein largely determines its secondary and tertiary structures.

Question 71

Proteins with quaternary structures have structures involving two or more ___ that are independent of each other.

Question 72

Tertiary structure for some proteins sometimes include nonpeptide groups called ___, and proteins that require a such groups for biological activity are called ___ proteins.

Question 73

In a treatment called ___, a monoclonal antibody is combined with a radioisotope.

Question 74

If a biologically active protein is sufficiently changed in its conformation so that it no longer is biologically active, that protein has been ___.

Question 75

Enzymes that only catalyze the reaction of a particular stereoisomer are referred to as ___.

Question 76

A ___ inhibitor is a substance that attaches to an enzyme at sites other than the active sites causing the enzyme to lose its ability to bind with the appropriate substrate.

Question 77

Enzymes that are composed of more than one peptide chain and for which binding of a substrate to one active site affects the bonding of the substrate to other active sites are referred to as a(n) ___ enzyme(s).

Question 78

Given the following amino acids and their R groups:
glycine (R group is -H) - aspartic acid (R group is -CH₂COO^-)
cysteine (R group is -CH₂SH) - lysine (R group is -(CH₂)₄NH₃⁺)
Sketch a generic amino acid.

Question 79

Given the following amino acids and their R groups:
glycine (R group is -H) - aspartic acid (R group is -CH₂COO^-)
cysteine (R group is -CH₂SH) - lysine (R group is -(CH₂)₄NH₃⁺)
Which amino acid is not optically active?

Question 80

Given the following amino acids and their R groups:
glycine (R group is -H) - aspartic acid (R group is -CH₂COO^-)
cysteine (R group is -CH₂SH) - lysine (R group is -(CH₂)₄NH₃⁺)
Sketch cysteine.