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MCAT-Biochemistry > Enzymes > Flashcards

Enzymes Flashcards

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1
Q

What are enzymes?

A

Biological catalyst

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2
Q

Describe the effect of catalysts on a reaction…thermodynamics, equilibrium etc.

A

Catalysts do not impact the thermodynamics of a biological reaction nor does it impact equilibrium position

Increases reaction rate

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3
Q

Summarize the 6 key points of enzymes

A
  1. Lower the activation energy
  2. Increase the rate of reaction
  3. Do not alter the equilibrium constant
  4. Are not changed or consumed in the reaction
  5. Do not affect the over 🔼G (overall energy) of a reaction
  6. Are specific for a particular reaction or class of reaction
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4
Q

The molecules upon which a molecule acts are called _______

A

Substrates

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5
Q

What is enzyme specificity?

A

An enzyme will only catalyze a single reaction or class of reactions with its substrates

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6
Q

Give the 6 main classifications of enzymes

A
  1. Oxidoreductases
  2. Transferases
  3. Hydrolysis
  4. Leases
  5. Isomerases
  6. Ligases
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7
Q

What is the function of oxidoreductases?

A

They catalyze redox reactions of biological molecules

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8
Q

Oxidoreductases often have cofactors that act as an e,extrinsic carrier such as…

A

NAD+

or

NAPD+

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9
Q

In reactions catalyze by oxidoreductases, the electron donor is called the

A

Reductant

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10
Q

In reaction involving oxidoreductases, that accept electrons is called…

A

The oxidant

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11
Q

Enzymes with dehydrogenase or reductase in the name or usually…

A

Oxidoreductases

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12
Q

Enzymes in which oxygen is the final electron acceptor often include…… in their names

A

Oxidase

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13
Q

What are transferases?

A

Enzymes that catalyze the movement of a functional group from one molecule to another

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14
Q

What is the function of kinases?

A

Kinases catalyze the transfer of a phosphate group, generally from ATP, to another molecule

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15
Q

What are hydrolases?

A

Catalyze the breaking of a compound into 2 molecules using the addition of water

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16
Q

What is the name and function of the most common hydrolase on the MCAT?

A

Phophatase- cleaves the phosphate group from another molecule

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17
Q

What are peptidases, lipases and nucleases?

A

Hydrolases which break down proteins, nuclei acids and lipases

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18
Q

What are the functions of lyases?

A

Enzymes that catalyze the cleavage of a single molecule into 2 products

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19
Q

How are lyases different from hydrolases and oxidoreductases?

A

They do not require water and do not act as oxidoreductases

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20
Q

When are lyases refferred to as synthases and why?

A

Lyases are referred to as synthases when when they combine 2 molecules into one.

(Most enzymes also catalyze their reverse reactions)

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21
Q

What are isomerases?

A

Enzymes that catalyze the rearrangement of bonds within a molecule.

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22
Q

Some isomerases can be classified as …. depending on…

A

Oxidoreductases, transferases or lyases

Depending on the mechanism of their reaction

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23
Q

Isomerases also catalyze reactions between _____________ as well as _________ isomers

A

Stereoisomers

Constitutional isomers

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24
Q

What are ligases?

A

Enzymes that catalyze synthesis reactions, usually between large similar molecules and often require ATP.

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25
Q

Synthesis reactions with smaller molecules are usually are usually accomplished with…

A

Lyases

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26
Q

Where would ligases most likely appear on test day?

A

Nucleic acid synthesis and repair

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27
Q

What is an endergonic reaction?

A

A reaction that requires energy input 🔼G

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28
Q

What is an exogonic reaction?

A

A reaction which gives off energy 🔼G

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29
Q

Catalysts exert their effect by lowering the ___________ ______ of a reaction

A

Activation energy

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30
Q

How exactly, do catalysts help lower activation energy?

A

Makes it easier for substrates to achieve their transition state

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31
Q

What is a active site?

A

The location within the enzyme where the substrate is held during the chemical reaction

32
Q

What is the enzyme substrate complex?

A

The physical interaction between the enzyme and its substrate

33
Q

Describe the lock and key theory

A

-Suggest the enzyme’s active site(lock)is already the appropriate conformation for the substrate(key) to bind

34
Q

What types of bonding stabilizes spatial arrangement and efficiency of the enzyme?

A

Hydrogen bonding, ionic interactions and transient covalent bonds within the active site

35
Q

Which 2 competing theories compete to explain how enzymes and substrates interact?

A
  • Lock and key theory

- Induced fit Model

36
Q

Which of the 2 theories that explain how an enzyme interacts with a substrate is most accepted/most likely to come on test day?

A

Induced fit Model

37
Q

Describe the induced fit model

A

The substrate has induced to fit a change in the shape of the enzyme

Shape of the active site becomes truly complementary after the substrate begins binding to the enzyme

38
Q

Explain the thermodynamics in substrate-enzyme interactions as explained by the induced fit theory

A

The substrate inducing a change in the enzyme requires energy- this part of the reaction is endogonic

The product letting go releases energy- this part is exergonic

39
Q

What prevents substrates from interacting with the wrong enzymes, according to the induced fit theory?

A

A substrate of the wrong type will not cause the appropriate conformational shift in the enzyme

The active site won’t be adequately exposed, the transition state is not preferred and no reaction occurs

40
Q

What are cofactors and coenzymes?

A

Non-protein molecules required by enzymes.

Are usually small, so they can bind to the active site of an enzyme and participate in catalysis if a reaction

41
Q

How are cofactors and coenzymes involved in catalysis?

A

Usually by carrying charge through ionization, protonation and deprotonation

42
Q

Why are cofactors and coenzymes usually kept at low concentrations in cells?

A

So they can be recruited when needed

43
Q

What are apoenzymes?

A

Enzymes without their cofactors

44
Q

What are holoenzymes?

A

Enzymes containing cofactors

45
Q

Tightly bond cofactors or coenzymes that are necessary for enzyme function are called….

A

Prosthetic groups

46
Q

What may cause Thiamine deficiency?

A

Excessive alcohol consumption and poor diet

47
Q

What may Thiamine deficiency lead to?

A

Wernicke-Korsakoff syndrome

48
Q

What is thiamine?

A

An essential cofactors for several enzymes in cellular metabolism and nerve conduction

49
Q

What are the symptoms of Wernicke-Kersakoff syndrome?

A

Patients suffer a variety of neurological deficits including:

  • delirium
  • balance problems
  • in sever cases, the inability to form new memories
50
Q

Differentiate between cofactors and coenzymes

A

Cofactors- generally inorganic molecules or ions, often ingested Asia dietary minerals

Coenzymes- are small organic groups, often vitamins or derivatives of vitamins e.g. NAD+, FAD and coenzymes A

51
Q

What are the water soluble vitamins?

A

B complex vitamins and ascribed acid/vitamin C

52
Q

Why must water soluble vitamins be replenished often?

A

Because they are easily excreted

53
Q

What are the fat soluble vitamins ?

A

Vitamins A, D, E and K

54
Q

Why are fat soluble vitamins do not need to be replenished as much as their water soluble counterparts?

A

Are better regulated by partition coefficients, which quantify the ability of a molecule to dissolve in a polar vs. non-polar environment

55
Q

Enzyme reactions are not restricted to a single _________ or ____________

A

Cofactors

Coenzyme

56
Q

What is the other name for Vitamin B1?

A

Thiamine

57
Q

What is the other name for vitamin B2?

A

Riboflavin

58
Q

What is the other name for vitamin B3?

A

Niacin

59
Q

What is the other name for vitamin B5?

A

Pantothenic acid

60
Q

What is the other name for vitamin B6?

A

Pyridoxal phosphate

61
Q

What is the other name for vitamin B7?

A

Biotin

62
Q

What is the other name for vitamin B9?

A

Folic acid

63
Q

What is the other name for vitamin B12?

A

Cyanobalamin

64
Q

The concentrations of what substances affect how quickly a reaction will occur?

A

Substrate and enzyme

65
Q

What is saturation?

A

When adding more substrate to the enzymes no longer increase reaction rate due to all the active sites being occupied

66
Q

At saturation, enzyme is working at….

A

Maximum velocity- vmax

67
Q

What is the only way to increase vmax/ maximum velocity?

A

By increasing the enzyme concentration

68
Q

How is vmax increased in the cell?

A

This can be accomplished in the cell by inducing the expression of the gene encoding the enzyme.

69
Q

What does the Michaelis-Menten plot of enzyme kinetics show?

A

As the substrate amount increases, the enzyme is able to increase its rate of reaction until it reaches vmax

Adding more substrate after vmax is reached, there will be no increase of reaction.

70
Q

What does the Michaelis - Menten equation describe?

A

Describe how the rate of reaction, v, depends on the concentration of both the enzyme, [E], and the substrate, [ S] which forms product [P]

71
Q

State the occurrences at k1, k2 and k3

A

K1: Enzyme-substrate complexes form at a rate k1

K2: the ES complex can either dissociate at a rate k2

K3: the ES complex becomes E + P at a rate k3

72
Q

Show the equations relevant to product formation in enzyme reactions

A

K1: E+S-> ES

K2: ES-> E+ S

K3: ES-> E + P

73
Q

What is the Michealis-Menten equation?

A

v = vmax[S] /Km + [S]

Enzyme concentration will remain constant

74
Q

What does Km/ Michaelis constant mean?

A

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

75
Q

What does Km stand for?

A

Michaelis constant

76
Q

What can Km/ Michaelis constant be used to measure?

A

A measure of the affinity of the enzyme for its substrate.

The enzyme with the higher Km has the lower affinity for its substrate because it requires a higher concentration to be half saturated

MCAT-Biochemistry (3 decks)

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