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MCAT Biochem > 2 - Enzymes > Flashcards

2 - Enzymes Flashcards

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MCAT flashcards
1
Q

What health problem is linked with obesity

A

Hypertension - high blood pressure

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2
Q

Risks associated with hypertension

A

Increased risk of stroke, heart and kidney failure

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3
Q

Anti-hypertension medication

A

ACE inhibitor
Angiotensin-converting enzyme

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4
Q

How do enzymes affect thermodynamics/kinetics

A

No change in thermodynamics
Increases rate (kinetics) by lowering activation energy

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5
Q

7 characteristics of enzymes

A

Lower activation energy
Does not change Gibbs free energy of reaction
Increases rate of reaction
Does not change equilibrium constant
Not changed/consumed in reaction
Temperature and pH sensitive (and high salinity)
Specific for a particular (class of) reaction

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6
Q

Enzyme specificity

A

Will only catalyze a single reaction/class of reaction with substrates

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7
Q

6 types of enzymes

A

Oxidoreductase
Transferase
Lyase
Lygase
Hydrolase
Isomerase

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8
Q

What do oxidoreductases do

A

Transfer electrons in redox reactions - often have cofactors (electron carrier)
Dehydrogenase/reductase
Oxidase - oxygen is final electron acceptor

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9
Q

What do transferases do
What is a subtype of transferase

A

Move functional group
Kinase - phosphate group

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10
Q

What do hydrolases do
Specific types of hydrolases

A

Break a compound into 2 using water
Phosphatase - cleaves phosphate group
Peptidase - cleaves protein
Nuclease - cleave nucleic acid
Lipase - cleave lipid

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11
Q

Lyase function

A

Cleave molecules without water
Synthesizing small molecules is done by synthase

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12
Q

What do isomerases do

A

Rearrange bonds in molecules - constitutional or stereoisomers
Can be oxidoreductases, transferases, lyases

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13
Q

Ligase function

A

Catalyze addition/synthesis reactions in larger molecules with ATP
Nucleic acid synthesis and repair

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14
Q

Endergonic reaction

A

Gibbs free energy > 0, requires energy

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15
Q

Exergonic reaction

A

Gibbs free energy < 0, release energy

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16
Q

How can enzymes make a reaction more favorable

A

Alter charge or pH
Stabilize transition state
Bring reactive groups closer together in active site

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17
Q

What dictates specificity of enzyme

A

Active site

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18
Q

Lock and key theory

A

Active site is ready for substrate to bind

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19
Q

Induced fit model

A

Alters active site when substrate is present (endergonic)
Releasing substrate to relaxed state (exergonic)

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20
Q

How to cofactors and coenzymes participate in reaction

A

Ionization, protonation, deprotonation

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21
Q

Apoenzyme

A

Enzyme without cofactors

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22
Q

Holoenzyme

A

Enzymes with cofactors

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23
Q

Prosthetic groups

A

Tightly bound cofactors/coenzymes needed for enzymatic function

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24
Q

Cofactors characteristics

A

Inorganic, metal ions that are ingested as minerals

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25
Q

Coenzymes characteristics

A

Organic, vitamins or derivatives of

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26
Q

Water-soluble vs fat-soluble vitamins

A

Water - B, C (polar)
Fat - A, D, E, K (Nonpolar)

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27
Q

B1 name and function

A

Thiamine - change carbs to energy in nervous system (brain)

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28
Q

B2 name and function

A

Riboflavin - heat-stable, change carbs, fats, proteins into glucose

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29
Q

B3 name and function

A

Niacin - antioxidant for immune system, hair, skin

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30
Q

B5 name and function

A

Pantothenic acid - healthy skin, hair, eyes, liver

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31
Q

B6 name and function

A

Pyridoxal phosphate - brain development, healthy immune and nervous systems

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32
Q

B7 name and function

A

Biotin - hair, nails, nervous system

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33
Q

B9 name and function

A

Folic acid - RBC formation, cell growth and function, control homocysteine in blood

34
Q

B12 name and function

A

Cyanocobalamin - normal development and myelination and CNS, RBC formation, DNA synthesis

35
Q

What are enzyme kinetics affected by

A

Environmental conditions, [substrate] and [enzyme]

36
Q

Saturation

A

Reaction rate cannot go faster because all enzymes are working at max velocity

37
Q

How to increase vmax

A

Increase enzyme concentration by upregulating gene expression

38
Q

What does Michaelis-Menten plot show

A

The rate of the reaction (v) depending on concentrations of the enzyme, substrate, and product

39
Q

What is the Michaelis constant? What does it mean

A

Km used to compare enzymes
Concentration at which half of the enzyme’s active sites are full
Cannot be changed with concentration of [S] or [E]

40
Q

What does high Km mean

A

Low affinity for substrate because more of it is needed to reach half the enzymatic activity

41
Q

What does low Km mean

A

High affinity for substrate because only a little is needed to reach half the enzymatic activity

42
Q

What does kcat measure

A

Sumner of substrate molecules converted to product per enzyme per second

43
Q

What does kcat measure

A

Number of substrate molecules converted to product per enzyme per second
Usually between 101-103

44
Q

What does vmax mean

A

Maximum enzyme velocity in moles of enzyme per second

45
Q

How is vmax related to kcat

A

vmax = [E]kcat

46
Q

What does kcat/Km show

A

Catalytic efficiency
High efficiency has high turnover or high substrate affinity

47
Q

What does kcat/Km show

A

Catalytic efficiency
High efficiency has high turnover or high substrate affinity

48
Q

What is the linear version of the Michaelis-Menten equation called? When is it useful

A

Lineweaver-Burk plot
Good to determine type of inhibition enzyme experiences

49
Q

How do cooperative enzymes look different on Michaelis-Menten graph

A

S-shaped

50
Q

What do cooperative enzymes have

A

Multiple subunits and active sites where the transition of one subunit influences other subunits

51
Q

What are the 2 states of cooperative enzymes

A

Low-affinity Tense state and high-affinity relaxed state

52
Q

How is the role of cooperative enzymes different than other enzymes

A

Often regulatory enzymes in pathways

53
Q

Hill’s coefficient

A

Quantifiable cooperativity

54
Q

Hill’s coefficient < 1

A

After a ligand binds, it decreases affinity of enzyme for more ligands

55
Q

Hill’s coefficient > 1

A

After a ligand binds, increases affinity of enzyme for more ligands

56
Q

Hill’s coefficient = 1

A

No cooperative binding

57
Q

What factors influence enzyme activity

A

Temperature, pH, high salinity

58
Q

How does temperature influence enzyme activity

A

Enzyme doubles velocity every 10°C increase until optimal temperature is reached
Past that optimal temperature, enzymes are easily denatured or they can revert back if cooled down

59
Q

How does pH affect enzyme rate

A

Ionization of active site, can denature enzyme

60
Q

What are the optimal pH for enzymes

A

General - 7.4
Pepsin (stomach) - 2
Pancreatic enzymes (small intestine) - 8.5

61
Q

How does salinity affect enzyme velocity

A

Problems in vitro
Disrupt H- and ionic bonds, partially change conformation of enzyme (3° and 4°), denaturation

62
Q

Feedback regulation

A

Regulation by products further down a pathway

63
Q

Feed-forward regulation

A

Regulation by intermediates that precede enzyme in pathway

64
Q

Main purpose of feedback inhibition

A

Negative feedback - helps maintain homeostasis by having the product bind to an enzyme earlier in the pathway

65
Q

4 types of reversible inhibition

A

Competitive, noncompetitive, mixed, uncompetitive

66
Q

How does competitive binding work? How does it affect vmax and Km

A

Binds to active site
No change in vmax
Increases Km because more substrate is needed to reach halfway

67
Q

How does noncompetitive binding work? How does it affect vmax and Km

A

Binds to allosteric site changing enzyme conformation - equal affinity for enzyme vs enzyme-substrate complex
Decreases vmax because there is less enzyme available to react
No change in Km

68
Q

How does mixed binding work? How does it affect vmax and Km

A

Inhibitor binds to allosteric site of enzyme or enzyme-substrate complex with different affinities
Decreases vmax
Increases Km if it binds to enzyme
Decreases Km if it binds to enzyme-substrate complex

69
Q

How does uncompetitive binding work? How does it affect vmax and Km

A

Only bind to enzyme-substrate complex preventing the release of the substrate
Decreases vmax and Km

70
Q

What is irreversible inhibition

A

Active site is unavailable for a long time or enzyme is permanently altered
More enzymes have to be made through translation

71
Q

Allosteric enzymes

A

Have multiple binding sites and can alternate between active and inactive form

72
Q

Allosteric site

A

Another site that can regulate availability of the active site

73
Q

Effect of allosteric activator

A

Conformational shift making the active site more available

74
Q

Effect of allosteric inhibitor

A

Conformational shift that makes the active site less available

75
Q

What are transient enzyme modifications

A

Allosteric activator and inhibitor

76
Q

What are covalent enzyme modifications

A

Phosphorylation, glycosylation

77
Q

Function of glycosylation

A

Attach sugar moieties to tag enzymes for transport within the cell or modify protein activity and selectivity

78
Q

Function of phosphorylation/dephosphorylation

A

Activate or deactivate enzymes

79
Q

Zymogen

A

Inactive enzyme state for transport that has a catalytic domain and regulatory domain

80
Q

How to expose active site on zymogen

A

Remove or alter regulatory domain

81
Q

What enzyme is similar in regulation to zymogens

A

Caspases/apoptotic enzymes

MCAT Biochem (2 decks)

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