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DAT Bio > Enzymes > Flashcards

Enzymes Flashcards

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1
Q

What is the role of an enzyme

A

They act as catalysts, lowering the activation energy of a reaction.

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2
Q

What are the six maor classes of enzymes?

A 
Isomerase
oxidoreductase
hydrolases
lyases
ligases
transferase
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3
Q

What does an isomerase do?

A

Transfer of groups within the same molecule. Molecular structure changes but nor molecular formula

Ex: Glucose-6-phosphate -> fructose-6-phosphate by phosphoglucoisomerase

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4
Q

What does an oxidoreductase do?

A

Catalyzes redox reactions, dehydrogenase is a type of oxidoreductase

Ex: Lactate + NAD+ -> Pyruvate + NADH
by lactate dehydrogenase

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5
Q

What do hydrolases do?

A

Cut bonds by using H20

Ex: Urea + H20 -> 2 NH3 + CO2
by Urease

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6
Q

What do lyases do?

A

Cut C-C, C-S, and some C-N bonds

Ex: CH3-CO-COO- -> CH3-COH + CO2

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7
Q

What do Ligases do?

A

Catalyzes formation of C-O, C-N, C-C and C-S bonds

Ex: CH3-CO-COO- + CO2 -> (COO-)-CH2-CO-COO-

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8
Q

What do transferases do?

A

Catalyzes group transfer.
glucose + ATP -> glucose-6-phosphate + ADP
by a kinase

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9
Q

What is Kcat

A

Turnover # - How quickly the substrate is used in the enzyme

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10
Q

Holoenzyme

A

The active enzyme with the non-protein portion

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11
Q

Apoenzyme

A

The inactive enzyme - without the non-protein portion

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12
Q

cofactor

A

an ion like Zn+2 or Fe+2 that binds to an enzyme to activate it.

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13
Q

coenzyme

A

a small organic molecule that binds to an enzyme to activate it.

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14
Q

prosthetic group

A

When a coenzyme binds covalently with an enzyme

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15
Q

What do enzymes change?

A

They change the activation energy of the reaction (ΔG* or Ea)

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16
Q

What don’t enzymes change?

A

ΔG, ΔH, Equilibrium, Keq constant, or product amount

17
Q

Km

A

The affinity of the enzyme for it’s substrate.

It reflects the substrate concentration that allows us to achieve 1/2 Vmax

18
Q

What does a large Km mean? What does a small one mean?

A

A large Km means that an enzyme has a low affinity for the substrate, it takes a lot more substrate to achieve 1/2 Vmax

A small Km means that an enzyme has a high affinity for the substrate, it doesn’t take a lot of substrate to achieve 1/2 Vmax

19
Q

Explain how Vmax is affected by concentration of solutes

A

At the very beginning of the addition of solute, there is a linear relationship with Vmax, a 1st order relationship. Then as more solute is added the relationship becomes mixed order (no longer linear) at Vmax the relationship is 0 order meaning that the reaction has achieved the max speed and adding more solutes won’t increase the rate of reaction.

20
Q

What does the Kcat / Km ratio tell us?

A

It tells us enzyme efficiency.
We want a high Kcat and a low Km to be highly efficient.

High Kcat means the enzyme catalyzes the substrate quickly, and a low Km means the enzyme has a high affinity for the substrate.

21
Q

What is a competitive inhibitor and how does it affect Vmax and Km

A

A competitive inhibitor binds to the same active site as the substrate inhibiting the substrate from being catalyzed.

Vmax is unchanged. You could eventually add enough substrate that the max reaction rate could be reached.

Km is changed. It affects the apparent Km, increasing it because the affinity of the enzyme to bind with the substrate is in essence changed.

22
Q

What is a non-competitive inhibitor and how does it affect Vmax and Km

A

A non-competitive inhibitor binds to a site distant from the active site. This changes the conformation of the enzyme, making it no longer functional.

Vmax decreases because the enzymes are essentially removed from the equation when they’re inhibited. Increasing substrate won’t overcome this change and so the new Vmax is only calculated with the remaining enzymes

Km is unchanged. It cannot be overcome by adding more substrate.

23
Q

What is an un-competitive inhibitor and how does it affect Vmax and Km

A

Similar to non-competitive inhibition, it binds to a site away from the active site, but an uncompetitive inhibitor only binds to the enzyme when it is an Enzyme substrate complex.

The Vmax is lowered because the enzyme undergoes a conformational change making it useless.

Km decreases because as the E-S complexes are inhibited they become an ESI complex completely different from the initial reactants. Le Chatliers principle moves the direction toward the formation of more ES complex, in essence changing Km in the direction of higher affinity (lower Km)

24
Q

Zymogen

A

The inactive form of an enzyme.

Can be converted to Zymogen by uncompetitive or noncompetitive inhibition.

Zymogens are often activated by proteolytic cleavage (the breaking of a peptide bond)

Zymogen-ABC –cut–> Active Enzyme-A + BC

25
Q

What is the difference between digestion and denaturing?

A

In digestion, the 1º, 2º, 3º, and 4º structure of the protein is changed.

In denaturing, only the 1º, 2º, 3º, and 4º structure of the protein is changed.

26
Q

How does temperature affect protein?

A

Temperature increases - disrupts bonding interactions

27
Q

How does radiation affect protein?

A

Disrupts native conformation

28
Q

How does mechanical agitation affect protein?

A

Violent mixing like in a blender, or shaking. Will cause polypeptide chains to unfold.

29
Q

How does pH affect protein?

A

Causes groups to gain or lose charges, disrupting bonding interactions

30
Q

How do salts of heavy metals affect protein?

A

Pb++, Hg+, Ag+ in particular react with SH (sulfhydyl groups) and prevent disulfide bond

31
Q

How do organic solvents (soaps, detergents, urea, alcohol) affect protein?

A

disrupts bonding interactions like hydrogen bonds

ex: alcohol passes through the cell wall of bacteria and destroys their proteins

32
Q

How do oxidizing and reducing agents affect protein?

A

Can form disulfide bonds or destroy them.

33
Q

isozymes

A

Enzymes that catalyze the same reactions, but differ in structure. They may differ a bit in Km and Vmax values

34
Q

Feedback inhibition

A

The final product will start to bind with an enzyme at the beginning of the reaction series in an inhibition to slow down the reaction.

35
Q

allosteric enzyme

A

An enzyme that undergoes a conformational change when binding with inhibitors or activators

They do not follow the same Vmax curve. They have a sigmoidal curve instead

DAT Bio (46 decks)

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