Properties of Enzymes Flashcards

1
Q

Catalysts

A

Increase the rate that equilibrium is reached by lowering the activation energy for a process

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2
Q

Substrate

A

What an enzyme acts on

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3
Q

Oxidoreductases

A

Class of enzymes
Catalyze oxidation-reduction reactions
Usually require a coenzyme like NAD+ or NADP+

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4
Q

Coenzyme

A

Molecules that supply enzymes with additional functional groups needed for reactions

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5
Q

Transferases

A

Class of enzymes
Catalyze functional group-transfer reactions
May require coenzymes

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6
Q

Hydrolases

A

Class of enzymes

Catalyze hydrolysis of bonds

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7
Q

Lyases

A

Class of enzymes

Catalyze lysis of a substrate (elimination reactions)

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8
Q

Synthases

A

Lyases that catalyze addition reactions

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9
Q

Isomerases

A

Class of enzymes

Catalyze interconversion between isomers

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10
Q

Ligases

A

Class of enzymes
Catalyze joining of 2 substrates
Often require energy from ATP to drive reaction

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11
Q

Initial velocity of enzymatic reaction

A

Vo= k2 [ES]

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12
Q

Steady-state approximation

A

Period of time (usually at the beginning of a reaction) where the ES complex is formed at the same rate as it decomposes, so that there is no net change in the [ES]

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13
Q

Michaelis-Menten equation

A

Vo=k2[ES]=(Vmax[S])/(Km+[S])

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14
Q

kcat (catalytic constant)

A
kcat= (moles of substrate -> product)/[(second)(moles of enzyme)]
Vmax= kcat[E total]
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15
Q

Km (Michaelis constant)

A

Measure of affinity of the enzyme for the substrate

Km=[S]=0.5Vmax

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16
Q

Catalytic proficiency

A

Effectiveness of an enzyme

17
Q

Lineweaver-Burke plot

A

Plot 1/Vo (y-axis) vs. 1/[S] (x-axis)
Y-intercept is 1/Vmax
X-intercept is -1/Km

18
Q

Inhibitor

A

Compound that binds to an enzyme and interferes with its activity

19
Q

Reversible inhibitor

A

Binds enzyme via noncovalent forces

20
Q

Irreversible inhibitor

A

Binds enzyme covalently
“Kills” enzyme
Example: organophosphorus inhibitors (sarin: nerve gas)

21
Q

Competitive inhibitor

A
Most common mode of enzyme inhibition
Binds free enzyme molecule only
Competes with substrate for binding
Doesn't affect Vmax
Raises Km
22
Q

Uncompetitive inhibitor

A

Binds ES complex (not free enzyme)
Usually only occurs with multisubstrate reactions
Lowers both Vmax and Km

23
Q

Noncompetitive inhibitor

A

Can bind to enzyme or ES complex
Don’t bind at same site as substrate
Decreases Vmax
Doesn’t affect Km

24
Q

Affinity labels

A

Irreversible inhibitors with affinity for an enzyme’s active site
Useful in determining which residues are critical for enzymatic activity or are proximal to substrate binding

25
Allosteric enzymes
Don't follow Michaelis-Menten kinetics (sigmoidal plot instead of line) Enzymatic activities are changed by metabolic activators and inhibitors (molecules that don't resemble substrates or products) Exhibit cooperativity
26
Regulation by covalent modification
Method of controlling enzyme activity through phosphorylation More permanent that allosteric modification, but can be reversible
27
6 categories of enzymes
``` Oxidoreductases Transferases Hydrolases Lyases Isomerases Ligases ```