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Biochemistry PMY-3 > Enzymes 2 > Flashcards

Enzymes 2 Flashcards

1
Q

What is kinetics ?

A

The study of rate of change from reactants to products

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2
Q

What is velocity?

A

Velocity(v) is the chance in conc. Of substrate or product per unit time

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3
Q

What is Rate(k)?

A

Rate(k) is the change in total quantity (of reactant or product) per unit time

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4
Q

What is the initial velocity(Vo)?

A

Initial velocity (Vo) is the change in reactant or product conc. during the linear phase of a reaction

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5
Q

What are the 3 basic assumptions of Michaelis Menten Kinetics?

A
  1. At anytime, there are more substrates than enzymes- the percentage of the total substrate bound by enzyme at any one time is small
  2. Steady-state assumption: the rate of formation of ES is equal to that of breakdown of ES(to E+S and to ECP).
    concentration of ES doesn’t change with time
  3. If all enzymes in the ES /active sites of enzymes are bound, then rate of the product formation is maximal:

Vmax = k2[ES]

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6
Q

Give the equation of the steady state equation

A

K1: E+S -> ES

K-1: ES -> E+S

K2: E+P -> ES

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7
Q

What is the Michaelis Menten equation?

A

A quantitative description of the relationship between the rate of an enzyme catalyzed reaction v1, substrate concentration [S], the M-M rate constant (Km) and maximal velocity (Vmax)

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8
Q

Give the Michealis Menten equation

A

v1= Vmax[S]/ (Km+[S])

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9
Q

What is the Michealis constant/ Km?

A

Km is equal to the concentration of substrate required to attain half maximal velocity for any given reaction

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10
Q

What is Vmax/ max velocity?

A

The max velocity- all the active sites on all enzymes are being used

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11
Q

How to find Km on a velocity substrate concentration graph?

A

Km = [S] where velocity is 1/2 Vmax

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12
Q

What is a first order reaction?

A

When substrate concentration is much less than Km, the velocity of the reaction is approximately proportional to the substrate concentration

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13
Q

What is a zero order reaction?

A

When the substrate concentration is much greater than Km, the velocity is constant and equal to Vmax. The rate of reaction becomes independent of substrate concentration. This demonstrates enzyme saturation

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14
Q

What is the reaction order at low concentrations and why?

A

At low concentration [S]&laquo_space;Km the velocity of the reaction is first order-proportional to substrate concentration

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15
Q

At high concentrations[S] what order is the reaction?

A

At high concentrations of substrate [S] &raquo_space;Km, the velocity is constant and independent of substrate concentration

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16
Q

How does reaction order change as reaction proceeds?

A

Reactions starts at first order, dependent on amount of substrate bound to enzymes, but as all enzymes become bound, the reaction become zero order and constant velocity is independent to [S] as all enzymes active sites are occupied

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17
Q

Define the correlation of Km and enzyme affinity

A

Large Km- reflects low affinity of enzyme for the substrate

Small Km- reflects a high affinity of enzyme for the substrate

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18
Q

Km and Vmax are__________

A

Independent

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19
Q

Enzyme A starts the reaction with less substrate, what does this indicate?

A

Enzyme A has a higher affinity for the substrate than enzyme B/ A has a smaller Km

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20
Q

How can Km be changed?

A

It is characteristic of an enzyme and cannot be changed

21
Q

How can Vmax be changed?

A

Vmax increases with higher enzyme concentration but Km stays the same

22
Q

Describe the lineweaver -Burk analysis

A
  • Lineweaver and Burk manipulated the MM equation by taking its reciprocal values generating a double reciprocal plot
  • leads to a linear graph of the reciprocals of velocity and substrate concentration
23
Q

What is the lineweaver Burk equation?

A

1/Vo= Km/vmax x 1[S]+ 1/Vmax

24
Q

What are inhibitors?

A

Substances that reduce the rate of enzymatic reactions

Decreases velocity by binding to the enzyme

25
Q

How do enzyme inhibitors work?

A

They are usually specific, work at low concentrations

They block the enzyme, but usually do not destroy it

26
Q

What are real life examples of enzyme inhibitors?

A

Many drugs and poisons inhibitors of enzymes in the nervous system

Elg. Sedatives, metal complexes, substrate analogues

27
Q

What is irreversible inhibition?

A

Irreversible inhibitor drugs or poisons bind covalently to the enzyme

This leads to an abnormal protein and degraded enzymes and permanently inactivating the enzymes

28
Q

Give examples of irreversible inhibitors

A

Heavy metals (Hg2+, Pb2+, Cd2+)

29
Q

What is reversible inhibitors?

A

Drugs bind noncovalently to the enzyme and so, can dissociate

30
Q

What are the classes of reversible inhibitors?

A

Competitive inhibitors(common)

Non competitive inhibitors

31
Q

What are competitive inhibitors?

A

Inhibitors that compete for the same active site as substrate and resemble normal substrate, e.g. protease inhibitors, a very successful class of antiretroviral drugs used to treat HIV

32
Q

What are non competitive inhibitors?

A

A substance that interacts with the enzyme, but usually not at the active site

33
Q

How can competitive inhibitors be dislodged?

A

By increasing the amount of substrate

34
Q

Give examples of competitive inhibitors

A
  • methanol and ethylene glycol compete with ethanol for the binding sites on alcohol dehydrogenase
  • methotrexate competes with folic acid for dihydrofolate reductase

(Hence why cancer patients need more folic acid for red blood cell production)

35
Q

How does competitive inhibition affect Vmax?

A

Vmax remains the same in competitive inhibition

NB: in LB graph, thus means the pass through y axis at same point, MM graph, same Vmax

36
Q

How does competitive inhibition affect Km?

A

Km is increased in the presence of a competitive inhibitor (on both graphs Km and 1/Km is pushed to the right on the X axis)

37
Q

What is a medical application of competitive inhibitors?

A

Statins- e.x. Lovastatin(or other statins) in treating hypertension or heart disease

38
Q

What is the mechanism of action of statin

A

Medication increases hyperlipedaemia

Same configuration as HMG-CoA(substrate) and lovastatin binds to HMG CoA reductase, preventing HMG CoA from binding

39
Q

Where do non competitive inhibitors bind?

A

Binds to somewhere else from active site and changes how performs

40
Q

How do non competitive enzymes affect Km?

A

Michealis constant does not change in the presence of inhibitor

On LB graph, both lines start at the same point (1/Km) and crosses y axis and different points

41
Q

How is Vmax affected by non competitive inhibition?

A

Maximal velocity is decreased at non competitive inhibition

Non competitive inhibitor reaction will have a higher 1/Max as a result(cross the y axis at different points)

42
Q

What is uncompetitive inhibition?

A

Inhibitor binds to ES complex, usually reversible

43
Q

How does uncompetitive inhibition graph look?

A

1/v and 1/Km are all different, set of parallel lines

44
Q

Give examples of irreversible inhibitors?

A

Permanently inactive enzymes

Heavy metals

Aspirin acetylates- used to reduce risk of heart attack

Fluorouracil- used for cancer patients

Orangophosphates- farmers use this for wheat control(can poison us)

45
Q

What is product inhibition?

A

Product of a reaction, will decrease the rate of reaction(is reversible)

This is used to regulate pathways, such as metabolism

46
Q

What is the kinetic effect of uncompetitive inhibitors?

A

Appearing Vmax decreased and Km is decreased

47
Q

Differentiate non competitive inhibitor and uncompetitive inhibitor via their binding sites

A

Noncompetitive-binds to E or ES complex other than catalytic site

Enzyme cannot form products

Uncompetitive - binds only to ES complexes at locations other than the catalytic site

Modified enzyme structure, preventing binding site from being available

48
Q

Which inhibitors can be reversed by substrate?

A

Only competitive inhibition

Biochemistry PMY-3 (37 decks)

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