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Medical Biochemistry > Ch. 6: Enzymes & Regulation > Flashcards

Ch. 6: Enzymes & Regulation Flashcards

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USMLE® Step 1 flashcards
1
Q

6 major classes of enzymes? (IUBMB System)

A

1) oxidoreductases
2) transferases
3) hydrolases
4) lyases
5) isomerases
6) ligases

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2
Q

What are oxidoreductases?

A

Oxidation-reduction reactions

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3
Q

What are transferases?

A

Transfer of C, N, or P containing groups

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4
Q

What are hydrolases?

A

Cleavage of bonds via addition of water

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5
Q

What are lyases?

A

Cleavage of C-C, C-S, & certain C-N bonds

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6
Q

What are isomerases?

A

Racemization of optical/geometric isomers

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7
Q

What are ligases?

A

Formation of bonds bet. C and O, S,N coupled to hydrolysis of high-energy phosphates

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8
Q

Reactions occurring in mitochondria?

A

1) TCA cycle
2) Fatty acid oxidation
3) Decarboxylation of pyruvate

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9
Q

Reactions occurring in cytosol?

A

1) glycolysis
2) hexose monophosphate shunt (HMP pathway)
3) fatty acid synthesis

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10
Q

Reactions occurring in nucleus?

A

DNA & RNA synthesis

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11
Q

Reactions occurring in lysosomes?

A

Degradation of complex macromolecules

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12
Q

2 factors governing rate of enzyme-catalyzed reactions?

A

1) temperature

2) pH

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13
Q

Curve shape of enzymes following Michaelis-Menten kinetics?

A

Hyperbolic

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14
Q

Curve shape of allosteric enzymes?

A

Sigmoid

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15
Q

Equation for Michaelis-Menten kinetics?

A

Vo = Vmax * [S] / Km + [S]

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16
Q

What does a high Km mean?

A

Enzyme has ⬇️ affinity for substrate

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17
Q

What does a low Km mean?

A

Enzyme has ⬆️ affinity for substrate

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18
Q

At 1/2 Vmax, what is Km?

A

Km = [S]

19
Q

What is a first order reaction?

A

[S] &laquo_space;Km

[S]⬆️, v ⬆️

20
Q

What is a zero order reaction?

A

[S]&raquo_space; Km

v constant & equal to Vmax, independent of [S]

21
Q

What is turnover number?

A

substrate converted to product/enzyme/unit time

22
Q

Equation for Lineweaver-Burke plot?
X-axis?
Y-axis?
Slope?

A

1/v = Km / Vmax * [S] + 1 / Vmax

X-axis = -1 / Km
Y-axis = 1 / Vmax
Slope = Km / Vmax
23
Q

What is a reversible inhibitor?

Types?

A

Binds enzyme via non-covalent bonds

1) competitive
2) noncompetitive
3) uncompetitive

24
Q

What is competitive inhibition?

A

Structural analog of substrate binds to active site on enzyme

Km ⬆️, Vmax stays same

25
Q

4 circumstances for competitive inhibition?

A

1) analogs compete w/S to bind @ active site on E
2) in 2S E catalyzed rxn, ⬆️ [2nd S] competes w/first for binding
3) in freely reversible rxn, P functions as inhibitor
4) in rxn w/metal ion cofactors, similar metal ions compete for same binding site on E

26
Q

Describe Michaels-Menton & Line weaver-Burke plot graphs for competitive inhibition?

A

Km ⬆️, Vmax stays same

Curve slopes up at lower X value (MM)
Straight line slopes higher, through same Y-intercept, different X-intercept (LB)

27
Q

What is noncompetitive inhibition?

A

Inhibitor not structurally similar to S
Inhibitor binds to different site from S binding site on E (inactivates via binding to free E or ES complex)

Vmax ⬇️, Km stays same

28
Q

Describe Michaels-Menton & Line weaver-Burke plot graphs for noncompetitive inhibition?

A

Vmax ⬇️, Km stays same

Curve flattens at lower Y value (MM)
Straight line slopes higher, through same X-intercept, different Y-intercept (LB)

29
Q

What is uncompetitive inhibition?

A

Inhibitor binds to ES complex ➡️ forms ESI complex

Km and Vmax change

30
Q

Describe Michaels-Menton & Line weaver-Burke plot graphs for uncompetitive inhibition?

A

Vmax & Km change

Curve slopes up at lower X value, flattens at lower Y value (MM)
Parallel lines, smaller X intercept, larger Y intercept (LB)

38
Q

What is a irreversible inhibitor?

A

Reacts act/near active site of enzyme, covalently modifies active site OR binds so tightly that dilution of EI complex doesn’t provide recovery of E activity

39
Q

2 examples of irreversible inhibition?

A

AchE: inhibited by organophosphorus compounds (sarin gas)

Cytochrome oxidase: inhibited by cyanide (CN-)

40
Q

How is cytochrome oxidase reactivated?

A

Nitrites (NaNO2), makes MetHb ➡️ higher affinity for CN- than cytochrome oxidase

41
Q

2 types of regulation?

A

Regulatory enzymes: catalyze rate-limiting step or committed step

Feedback inhibition by end product

42
Q

What are allosteric enzymes?

A

Regulated by non-covalent interactions of compounds at sites besides the catalytic site

Rate determining enzymes

43
Q

What are the ligands that regulate at allosteric sites?

A

Effectors, modulators, or modifiers

44
Q

Type of graph for allosteric enzymes?

A

Sigmoidal (does not follow MM kinetics)

45
Q

What is cooperativity?

A

How binding of ligand at allosteric site affects binding of same or another ligand to enzyme

Can be positive (activatory, ⬆️ affinity for S) or negative (inhibitory, ⬇️ affinity for S)

46
Q

What are homotropic interactions in allosteric enzymes?

A

Same ligand positively influences cooperativity bet diff modulator sites

47
Q

3 features of homotropic enzyme graph?

A

[S] = + modulator
K0.5 = 1/2Vmax (not Km)
Vmax at high [S]

48
Q

What are heterotropic interactions in allosteric enzymes?

A

Effect of one ligand on binding of diff ligand

49
Q

Features of heterotropic graph: same Vmax, changed K0.5

A

+ modulator: ⬇️ K0.5

  • modulator: ⬆️ K0.5
50
Q

Features of heterotropic graph: changed Vmax, same K0.5

A

+ modulator: ⬆️ Vmax

  • modulator: ⬇️ Vmax
51
Q

2 examples of allosteric enzymes?

A

Asp transcarbamoylase (ATCase): CTP (- modulator), feedback inhibition; ATP (+ modulator)

Hemoglobin: homotropic = O2 binding, heterotropic = H+, CO2, 2,3-BPG

Medical Biochemistry (23 decks)

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