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Biochemistry > Enzymes and Inhibitors > Flashcards

Enzymes and Inhibitors Flashcards

1
Q

what is stereospecificity?

A

only acts upon one stereoisomer of a substrate

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2
Q

what is an oxidoreductase?

A

catalyses oxidation/reduction reactions

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3
Q

what are transferases?

A

catalyse group transfer reactions and require the presence of coenzymes

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4
Q

what are hydrolases?

A

catalyse hydrolysis

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5
Q

what are lysases?

A

catalyse lysis of a substrate

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6
Q

what are isomerases?

A

catalyse structural changes in a single molecule

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7
Q

what are ligases?

A

catalyse ligation e.g. joining of two substrates

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8
Q

what can ligases also be known as?

A

synthetases

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9
Q

what do ligases need in order to work?

A

ATP

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10
Q

what is an example of oxidoreductase function?

A

the formation of NAD+ by transferring a H ion from NADH

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11
Q

what happens in transferase function?

A

a portion of a substrate molecule binds covalently to an enzyme

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12
Q

what would you plot on a graph to calculate the Km value?

A

the velocity of the reaction against the substrate concentration, [S]

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13
Q

why does the graph begin to level off towards the Vmax value?

A

because all active sites of the enzyme are filled

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14
Q

what does a high Km value mean?

A

that there is a lower affinity of binding to the enzyme

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15
Q

how would you calculate the k of a reaction?

A

V=k[S]

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16
Q

what is a Lineweaver-Burg graph?

A

1/Vo against 1/[S]

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17
Q

what is useful about a Lineweaver-Burg graph?

A

gives a straight line and therefore gives more accurate values

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18
Q

what does the x-axis represent on the LB graph?

A

-1/Km

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19
Q

what does the y-axis represent on an LB graph?

A

1/Vmax

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20
Q

what type of interaction occurs between enzyme and a substrate?

A

transient non-covalent bond between the active sites

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21
Q

what are the two distinct steps in an enzymatic reaction?

A

formation of a complex and dissociation of the enzyme and product

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22
Q

what does energies K1 and K-1 control?

A

the association of E and S and the dissociation of S from ES

23
Q

what are the types of multi-substrate reactions?

A

ternary complex and ping pong

24
Q

what is a ternary complex reaction?

A

with substrates bind to the E at the same time to form EAB

25
Q

what does a ternary complex reaction look like on a V by [S] graph?

A

when there is a fixed amount of A and varying amount of B, the lines will intersect

26
Q

what is a ping pong reaction?

A

enzyme can be in a normal of chemically altered state, so A binds and alters the state, allowing B to bind to then regenerate the altered state

27
Q

what kind of enzymes show ping pong reactions?

A

some oxidoreductases and transfereases

28
Q

what are enzyme inhibitors?

A

small molecules that can bind reversibly

29
Q

how do artificial inhibitors bind?

A

using weak, non-covalent forces

30
Q

what effect does competitive inhibitors have on Vmax and Km value? why?

A

raises the Km due to when the amount of inhibitor concentration increases it causes less free enzyme so more substrate needed to reach the same v. The Vmax value is unchanged due to at a high substrate concentration the inhibitor is out competed and so the rate does not change

31
Q

what effect does uncompetitive inhibitors have on Vmax and Km value?

A

lowers the Vmax and the Km value due to the concentration of substrate not affecting the action of the inhibitor and the amount of ES complexes being reduced

32
Q

what does a LB graph with competitive inhibitors look like?

A

the same y-axis yet varying x-axis values

33
Q

what does a LB graph with uncompetitive inhibitors look like?

A

parallel lines crossing the graph

34
Q

how do non-competitive inhibitors effect the Vmax and Km values?

A

lowers the Vmax due to when the concentration of the inhibitor is increased it lowers the amount of free enzyme so lowered rate of reaction, Km stays the same due to the inhibitor binding away from the active site so that the enzymes affinity for the substrate does not change

35
Q

what does an non-competitive LB graph look like?

A

same X axis values yet different Y-axis values

36
Q

what happens in irreversible enzyme inhibition?

A

stable covalent bonds formed

37
Q

what causes irreversible enzyme inhibition?

A

alkylation or acetylation of the side chain of an active amino acid residue

38
Q

what causes regulated enzymes to become more active?

A

when the concentration of substrate or product increases

39
Q

what happens in repression of an allosteric enzyme?

A

active without signal molecules, active sites changed by repressors and not active in presence of signal molecules

40
Q

what happens in activation of allosteric enzymes?

A

not active in absence of signal molecules, activator signal molecules restore the active site and active with presence of signal molecules

41
Q

what do catalysts do?

A

create reaction pathways with a lower activation energy and stabilise transition states

42
Q

how does polar AA residues cause catalysis?

A

the active site contains a few hydrophilic polar residues which can then undergo chemical changes and cause catalysis

43
Q

what is acid-base catalysis?

A

this relies on the ability of AA side chains to donate or accept protons due to different amounts of dissociated H ions at different pH levels

44
Q

what is covalent catalysis?

A

substrate forms a transient covalent bond with the residues in the active site, adding an additional covalent intermediate to the reaction

45
Q

in covalent catalysis, what can differ with the side chains?

A

can be nucleophile or electrophile

46
Q

what occurs if the side chains in covalent catalysis are nucleophile?

A

bond formed by the side chains donating electrons or react at electron-poor sites such as protons

47
Q

what occurs if the side chains in covalent catalysis are electrophile?

A

bond formed by the side chains participate in the reactions by accepting an electron pair

48
Q

what are the two types of cofactors?

A

essential ions and coenzymes

49
Q

what are essential ions? what are the two types?

A

activator ions which are loosely bound and metalloenzymes which are tightly bound

50
Q

what is a metalloenzyme?

A

enzyme protein containing metal ions that are tightly bound

51
Q

what are the two types of coenzyme?

A

co-substrates and prosthetic groups

52
Q

what are prosthetic groups?

A

coenzyme that is tightly or covalently bonded to a protein

53
Q

what are co-substrate coenzymes?

A

enzymes that are transiently bound to the protein

Biochemistry (9 decks)

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