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MCAT Biochemistry > Chapter 2. Enzymes > Flashcards

Chapter 2. Enzymes Flashcards

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MCAT flashcards
1
Q

Fill in the blank.

The molecules that are acted on by enzymes are called ____.

A

substrates

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2
Q

What are ribozymes?

A

Biological catalysts composed of RNA instead of peptides.

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3
Q

What is the activation energy (Ea) of a reaction?

A

The input of energy needed to overcome the barriers in the reaction.

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4
Q

Finish the sentence.

Enzymes decrease the activation energy, so molecular collisions ____.

A

occur more often

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5
Q

What are the six classes of enzymes?

A
  • Oxidoreductases
  • Transferases
  • Hydrolases
  • Lyases
  • Isomerases
  • Ligases
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6
Q

What are oxidoreductases?

A
  • Class of enzymes that catalyze redox reactions.
  • Transfer electrons between biological molecules.
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7
Q

When looking at oxidoreductases, the ____ is the electron donor and the ____ is the electron acceptor.

A

reductant; oxidant

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8
Q

Fill in the blank.

Oxidoreductases often have a cofactor that acts as an ____.

A

electron carrier

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9
Q

Oxidoreductases often have a cofactor that acts as an electron carrier. Give an example of three cofactors associated with oxidoreductases.

A

NAD+, NADP+, and heme

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10
Q

Which class of enzyme catalyzes the movement of a functional group from one molecule to another?

A

Transferases

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11
Q

Fill in the blank.

Transferases often employ ____.

A

coenzyme donors

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12
Q

Transferases often employ coenzyme donors. Give an example of one common coenzyme donor associated with transferases.

A

Coenzyme A

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13
Q

Fill in the blank.

Kinases and polymerases are classified as a ____ enzyme.

A

transferase

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14
Q

What are kinases?

A
  • Transferase enzyme.
  • Catalyze the transfer of a phosphate group, generally from ATP, to another molecule.
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15
Q

What is a polymerase?

A
  • Transferase enzyme.
  • Catalyze the transfer of nucleotides.
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16
Q

Which class of enzyme catalyzes the breaking of a compound into two molecules using the addition of water?

A

Hydrolases

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17
Q

What is the reverse reaction of hydrolases?

A

Dehydration synthesis

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18
Q

What is a phosphatase?

A
  • Hydrolases enzyme.
  • Cleaves a phosphate group from another molecule.
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19
Q

Which type of enzyme catalyzes the cleavage of a single molecule into two products?

A

Lyases

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20
Q

Which group of enzymes often forms rings or multiple bonds to reform octets?

A

Lyases

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21
Q

Fill in the blanks.

Lyases require ____ phosphate group(s) to cleave molecules, and ____ phosphate group(s) to bring molecules together.

A

one; two

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22
Q

Which class of enzyme catalyzes the rearrangement of bonds within a molecule?

A

Isomerases

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23
Q

Fill in the blanks.

Isomerases interconvert between ____ and ____.

A

constitutional isomers and stereoisomers

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24
Q

Which class of enzyme catalyzes addition or synthesis reactions, generally between large similar molecules, and often require ATP?

A

Ligases

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25
Q

Which class of enzyme is typically encountered in the context of DNA repair/synthesis?

A

Ligases

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26
Q

What are the five ways that enzymes decrease the activation energy of a reaction?

A
  1. Stabilize the transition state.
  2. Microenvironment adjustments.
    1. Adjustment of the local’s environment pH.
    2. Through the exclusion of water.
  3. Adjusting substrate proximity.
    1. Increases the frequency of favorable collisions.
  4. Transient covalent bonding.
    1. Substrates briefly contact active site residues subsequentially.
  5. Reactant destabilization.
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27
Q

What are the three types of interactions that occur in the active site to stabilize the spatial arrangement and contribute to the efficiency of the enzyme?

A
  • Hydrogen bonding
  • Ionic interactions
  • Transient covalent bonding
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28
Q

What is the Lock and Key Theory?

A

The enzyme’s active site (lock) is already in the appropriate conformation for the substrate (key) to bind.

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29
Q

What is the Induced Fit Model?

A

The enzyme and substrate experience a change in the conformation during binding to increase complementary.

30
Q

What is the difference between coenzymes and cofactors?

A
  • Coenzymes
    • Extrinsic organic molecules.
    • A majority are vitamins.
  • Cofactors
    • Inorganic molecules.
    • Usually, positively charged metal ions.
      • Found in a negative environment.
31
Q

Coenzymes are organic molecules that are usually vitamins. Which vitamins are water soluble and which ones are fat soluble?

A
  • Water soluble
    • B, C
  • Fat soluble
    • A, D, E, K
32
Q

What is the difference between holoenzymes and apoenzymes?

A
  • Holoenzymes
    • When all the coenzymes and cofactors are available.
  • Apoenzymes
    • When not all the coenzymes and cofactors are available.
33
Q

In the following equation, what does kcat represent?

A

Measures the number of substrate molecules converted into products.

34
Q

What is the only way to increase the vmax ? How is it done in a cell?

A
  • Increase the enzyme concentration.
  • In the cell, this can be done by inducing the expression of a gene encoding the enzyme.
35
Q

In the Michaelis-Menten equation, what is the Km ?

A

The substrate concentration at which half of the enzyme’s active sites are full.

36
Q

Shown below is the Michaelis-Menten equation. What is v and what does it depend on?

A
  • v= rate of reaction
  • Depends on the concentration of enzyme and substrate to form the product.
37
Q

What is the relationship between Km and substrate?

A
  • Km is used to measure the affinity of an enzyme to a substrate.
  • As the Km value increases, the substrate affinity decreases.
38
Q

What is the equation used to calculate the catalytic efficiency?

A

kcat / K m

39
Q

Subunits and enzymes exist in two states. What are they?

A
  • A low-affinity tense state (T).
  • A high-affinity relaxed state (R).
40
Q

What is Hill’s coefficient?

A

A quantitative measure of cooperative binding effects in enzymes.

  • Hill’s coefficient > 1
    • Positive cooperative binding.
    • Binding affinity increase for the substrate.
  • Hill’s coefficient < 1
    • Negative cooperative binding.
    • Binding affinity decrease for the substrate.
  • Hill’s coefficient = 1
    • Non-cooperative binding.
    • Does not affect the affinity for the substrate.
41
Q

What is cooperativity?

A

The interaction between subunits of a multiple subunit protein in which binding of substrate to one subunit increases the affinity of other subunits for the substrate.

42
Q

Fill in the blank.

In cooperativity, the unbinding of the substrate from one unit ____ the affinity of other subunits for the substrate.

A

decreases

43
Q

What are the three local conditions that can have an effect on enzyme activity?

A
  • Temperature
  • pH
  • Salinity
44
Q

How does temperature have an effect on enzyme activity?

A
  • Every 10 degrees C doubles the rate of the reaction.
    • Until you reach 37 degrees C.
  • Enzymes can denature at higher temperatures and lose function.
45
Q

Fill in the blank.

Altering the pH can ____ an enzyme.

A

denature

46
Q

What is the pH of blood?

A

7.4

47
Q

What is the pH of the stomach?

A

2.0

48
Q

What is the pH of the small intestines?

A

8.5

49
Q

How does salinity have an effect on enzyme activity?

A

Hydrogen and ionic bonds may be disrupted, which can change the conformation of an enzyme.

50
Q

What is the difference between vitro and vivo?

A
  • Vitro = outside of the organism.
  • Vivo = inside of the organism.
51
Q

Fill in the blank.

____ feedback regulation helps maintain homeostasis.

A

Negative

52
Q

What is the difference between negative feedback regulation and positive feedback regulation?

A
  • Negative Feedback Regulation
    • Prevents the enzyme from working.
    • Helps maintain homeostasis.
    • Usually happens when there is enough product.
  • Positive Feedback Regulation
    • Product binds to the enzyme to make more of it.
53
Q

In the image shown, what does “A” and “B” represent?

A

A= 1/vmax

B= -1/Km

54
Q

What are the four types of reversible inhibition?

A
  • Competitive inhibition
  • Noncompetitive inhibition
  • Mixed imhibition
  • Uncompetitive inhibition
55
Q

What is competitive inhibition?

A
  • The inhibitor and the substrate fight to be in the active site.
  • The inhibitor does not react with the enzyme but instead sits there so the substrate cannot.

Binding site: active site

Impact on Km: increases

Impact on vmax : unchanged

56
Q

What is noncompetitive inhibition?

A
  • The inhibitor binds to the allosteric site and causes a conformational change to the enzyme so that the substrate cannot bind.
  • The inhibitor has equal affinity for the enzyme and the enzyme-substrate complex.

Binding site: allosteric site

Impact on Km: unchanged

Impact on vmax : decrease

57
Q

Competitive inhibition is when the inhibitor and the substrate fight to be in the active site. What is one way to overcome this inhibition?

A

Increase the concentration of the substrate.

58
Q

What is mixed inhibition?

A

Mixed inhibition results when an inhibitor can bind to either the enzyme of the enzyme-substrate complex, but has a different affinity for both.

Binding site: allosteric site

Impact on Km: increase or decrease

Impact on vmax : decrease

59
Q

Fill in the blank.

Mixed inhibition alters the value of ____.

A

Km

60
Q

Mixed inhibition alters the value of Km . When does the Km increase? Decrease?

A
  • If the inhibitor preferentially binds to the enzyme, Km increases (lower affinity).
  • If the inhibitor binds to the substrate-enzyme complex, Km decreases (higher affinity).
61
Q

What is uncompetitive inhibition?

A

Uncompetitive inhibition is when the inhibitor binds only to the enzyme-substrate complex and essentially locks the substrate in the enzyme, preventing its release.

Binding site: allosteric site

Impact on Km: decreases

Impact on vmax : decreases

62
Q

Which type of reversible inhibition is represented in the graph shown?

A

Competitive inhibition

63
Q

Which type of reversible inhibition is shown on the graph?

A

Noncompetitive inhibition

64
Q
  • What are allosteric enzymes?
A
  • Enzymes that are allosteric have multiple binding sites.
  • They alternate between an active form and an inactive form.
65
Q

Which reversible inhibitions use allosteric regulation?

A
  • Noncompetitive inhibition
  • Uncompetitive inhibition
  • Mixed inhibition
66
Q

What is irreversible inhibition?

A

The active site is made unavailable for a prolonged period of time, or the enzyme is permanently altered.

67
Q

What are the three types of regulated enzymes?

A
  • Allosteric enzymes
  • Covalently modified enzymes
  • Zymogens
68
Q

What are two examples of covalently modified enzymes? Explain.

A
  • Phosphorylation/Dephosphorylation
  • Glycosylation
69
Q

What is phosphorylation?

A

Adding a phosphate to an enzyme can activate it, and removing a phosphate to an enzyme can deactivate it.

70
Q

What is glycosylation?

A
  • Covalent attachment of sugar moieties.
    • Carbohydrate group tags enzyme for transport.
    • Can modify protein activity and selectivity.
71
Q

What is a zymogen?

A

The inactive form of an enzyme.

72
Q

A zymogen is an inactive form of an enzyme. It contains a ____ domain and a ____ domain.

A

catalytic; regulatory

MCAT Biochemistry (3 decks)

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