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Science for Medicine > SfM - Enzymes > Flashcards

SfM - Enzymes Flashcards

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1
Q

what is an enzyme?

A
  • globular protein

- biological catalysts (increases reaction rate)

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2
Q

what is a co-factor?

A

non-protein component needed for activity

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3
Q

what is a co-enzyme?

A

complex organic morecule

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4
Q

what is meant by a prosthetic group?

A

non-protein co-factor bond to the enzyme i.e Haem group

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5
Q

what is the difference between an apo/holo-enzyme?

A
  • apoenzyme = is the enzyme in its inactivated state i.e protein w/o co-factor
  • holoenzyme = the enzyme in its functional/active state with co-factor attached
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6
Q

what is a substrate?

A
  • molecule that is acted upon by enzyme
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7
Q

what is an active site?

A
  • part of the enzyme that the substrate binds and is acted upon
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8
Q

what is the function of enzymes?

A
  • increase rates of spontaneous reactions
  • lower the activation energy of biological reactions
  • accelerate movement towards reaction equilibrium
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9
Q

how do enzymes reduce activation energy?

A
  • enzymes force the substrates to be correctly orientated by binding them in correct formation needed for reaction to go
  • conformational changes occur in the protein structure when substrate binds
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10
Q

what is meant by enzyme kinetics?

A
  • study of chemical reactions between enzyme and substrate
  • More substrate you put in, the quicker the initial reaction velocity/speed (V0). Initially the reaction kinetics will produce a linear response as there is large amounts of enzyme and substrate – however, this will eventually plateau as substrate conc. is reduced and enzymes are saturated (active sites)
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11
Q

what is the rate limiting step of enzyme kinetics?

A

ES –> E + P

- reaction must be proportional to amount ES

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12
Q

what is Km?

A

the ratio of rate constant for:
breakdown of ES to E+S compared to
formation of ES from E+S
- indicates affinity of the enzyme for it’s substrate

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13
Q

what is Vmax?

A
  • tells you how fast a reaction is proceeding when the enzyme is saturated with substrate
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14
Q

what does a high Km and high Vmax mean?

A
  • lower affinity
  • requires greater conc to reach max
    (glucokinase - liver)
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15
Q

what does low Km and low Vmax mean?

A
  • high affinity
  • requires less to reach max
    (hexokinase - body)
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16
Q

how do glucokinase/hexokinase work?

A
  • blood glucose increases
  • glucokinase activity increases (liver hit with high conc of glucose)
  • hexokinase does not respond as it is continually working at Vmax (doesn’t take unnecessary glucose)
17
Q

what is an isoenzyme?

A
  • different enzymes that catalyse the same reaction (variable rates of reaction)
  • products of different genes
  • can be separated via electrophoresis
18
Q

what does an ordered sequential reaction mean?

A
  • there is specific order of binding and release of substrates of the reaction and then products
19
Q

what does a random sequential reaction mean?

A
  • it doesn’t matter if the substrate or the co-factor bind to enzyme first or what product is released first
20
Q

what is an allosteric enzyme?

A
  • large multi-subunit enzymes which contain many active sites
    (can host many reactions at the same time - either same or different)
21
Q

what will affect an enzyme?

A
  • temperature (increased temp = increase reaction rate. NOTE - could denature enzyme eventually)
  • pH (pH changes alter charge of amino acids - if active site aa charge is altered - enzyme ceases to function)
22
Q

what kind of enzyme inhibitors are there?

A
  • competitive inhibitor
    (enzymes non-covalently bind & compete w/ substrate for active site - usually resemble substrate)
  • uncompetitive inhibitor
    (bind to enzyme and affect reaction process w/o binding to active site)
  • non-competitive inhibitor
    (non-covalently bind to enzyme but not on active site)
23
Q

what happens when non-/competitive inhibitors are present?

A
  • presence of CI leads to a decrease in affinity to the substrate, so Km increases, however increasing substrate concentration can overcome this inhibition, so same Vmax
  • presence of n-CI, substrate is still able to bind to active site so Km stays same but Vmax decreases
24
Q

what is a transition state analogue?

A
  • as maximal interaction occurs between enzyme and the transition state rather than substrate, an analogue that mimics the transition state is created instead
25
Q

what is a catalytic antibody?

A
  • an antibody that is specific to a transition state molecule
26
Q

what is an irreversible inhibitor?

A
  • covalently bind to the enzyme, meaning it cannot be removed (cyanide)
27
Q

how are enzymes controlled?

A
  • feedback inhibition - some pathways prevent build-up of the end-product but turning off the enzyme when product conc gets too high
28
Q

what are allosteric effectors?

A
  • cell metabolites that bind non-covalently to a site that is not the active-site, this changes enzyme structure
  • can be activators or inhibitors (increase/decrease likelihood of binding)
29
Q

describe stages in concerted model

A
  • with no substrate the enzyme flips between open and closed conformation
  • when one molecule of substrate binds it locks other binding sites in open state, stopping them from flipping, allows more S to bind
  • allosteric activators - stabilise open conformation
  • allosteric inhibitors - favour closed formation
30
Q

describe stages in sequential model

A
  • substrate binding causes a change in one subunit
  • this causes a change in another sub-unit allowing to bind S more readily and so on…
  • there is sequential increase of affinity to substrate
31
Q

in what ways can enzymes be regulated?

A
  • covalent modification i.e phosphorylation/proteolytic cleavage
  • multiple phosphorylation sites allow fine control of enzyme - not on/off more of a dimmer switch
  • proteolytic cleavage - inactive precursor protein can be cleaved by proteases to give active form

Science for Medicine (9 decks)

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