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Biochemistry > L10: Enzymes I > Flashcards

L10: Enzymes I Flashcards

1
Q

Define enzyme structure

A

Proteins composed of 1 or more polypeptide chains folded into a 3D complex shape

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2
Q

How are enzyme structure stabilised?

A

By weak bonds

H-bonds
Electrostatic salt bridges
Van der Waals
Hydrophobic interactions

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3
Q

Define enzymes

A

Biological catalysts that speed up the rate of reaction, without altering the final equilibrium between reactants & products

Extremely efficient

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4
Q

2 theories for enzyme binding

A

1) Lock & Key
2) Induced Fit

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5
Q

lock & key

What is the lock & key theory?

A

Enzymes are complementary to their substrate

To explain the high specificity of enzymes

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6
Q

induced fit

What is the induced fit theory?

A

Enzymes are initially not complementary, but will undergo change upon substrate binding

Induced by weak interactions with the substrate itself

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7
Q

Define transition state

A

Unstable, high-energy intermediate in a chemical reaction, when the molecule is neither substrate/product

Stabilising the transition state is one way that enzymes can speed up a reaction

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8
Q

Why is the transition state high energy?

A

Has 5 carbon bonds

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9
Q

Why complementarity of enzymes to transition state necessary?

A

Lowering the Ea, binding tightly so reaction can’t proceed

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10
Q

Substrate specificity

What do enzymes usually do?

A

1) Catalyse only 1 type of reaction
2) Only act on a few related molecules

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11
Q

Substrate specificity

True or false: Enzyme will usually act only on one isomer if a compound exists in 2 steroisomer forms

A

TRUEEEE

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12
Q

What is specificity determined by?

A

Groove or cleft of defined shape - the ‘active site’

Which only the substrate of the correct shape & charge can fit

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13
Q

Enzyme specificity - classification

How many classes are enzymes divided in & according to what?

A

6 classes & according to the type of reaction they catalyse

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14
Q

enzyme specificity-classification

Are the six classes of enzymes further divided into subgroups? If yes, what is according to?

A

Yes, according to their substrate or source

Substrate: What they work on
Source: Where they come from

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15
Q

6 classification of enzymes

A

1) Oxidoreductases
2) Transferases
3) Hydrolases
4) Lyases
5) Isomerases
6) Ligases

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16
Q

classification of enzymes

What type of reaction is OXIDOREDUCTASES

A

Catalyse oxidation/reduction reactions

Transfer of H & O atoms/electrons from 1 substance to another

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17
Q

classification of enzymes

What type of reaction is TRANSFERASES

A

Catalyse the transfer of functional groups from 1 substance to another

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17
Q

classification of enzymes

What type of reaction is HYDROLASES

A

Catalyse the formation of 2 products from a substrate by hyrolysis (spitting using H2O)

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17
Q

classification of enzymes

What is the type of reaction LYASES

A

Catalyse non-hydrolytic addition or removal of groups from substrates

18
Q

classification of enzymes

What type of reaction is ISOMERASES

A

Catalyse isomerisation changes within a single molecule

19
Q

classification of enzymes

What type of reaction is LIGASES

A

JOin together 2 molecules by synthesis of new
C-O, C-S, C-N or C-C bonds
whilst breaking down ATP

20
Q

Properties of enzymes: effects of temp

Weak bonds are easily broke

A
  • Enzyme structure is stabilised by many weak bonds
  • Weak bonds are easily broken
  • Makes enzymes very sensitive to changes
21
Q

classification of enzymes

What type of reaction is TRANSLOCASES

A

Catalyse the movement of ions/molecules across membranes or their separation within membranes

22
Q

Define cofactors

A

Nin-protein substance (small organic molecules/inorganic elemtns), that is necessary for the activity of an enzyme

23
Q

Define co-enzymes

A

Organic cofactors that are not firmly attached to the enzyme

Non-protein substance

24
Q

Define apoenzyme

A

Enzyme represent inative becayse its been separated from its cofactors

Enzymes catalytically inactive form

25
Q

Define holoenzyme

A

Complete molecule in its fully active state

Enzymes catalytically active form

26
Q

2 examples of co-enzymes

A

1) NAD
2) FAD

27
Q

Another term for co-enzymes

A

Co-substrates, as they take part in & are changed by the reaction

28
Q

Define isoenzymes

A

Enzymes with different protein structures that catalyses the same reaction

Coded for by different genes

29
Q

Define enzyme kinetics

A

Study of the RATE of an enzyme catalysed reaction

  • How that rate varies with different substrate concentrations
  • Effects of inhibitors
30
Q

How is the reaction rate at low substrate concentration?

A

Reaction rate is directly proportional to the substrate concentration

31
Q

How is the reaction rate at high substrate concentration?

A

Reaction rate is independent of substrate concentration

32
Q

Define reaction rate

A

Increase in the amount of product formed per time

33
Q

How can the reaction rate be measured as?

A

Decrease in the amount of substrate per unit time

34
Q

Formula for Michaelis-Menten reaction model

A

S + E ⇌ ES → P + E

35
Q

What does the Michaelis-Menten reaction model explain?

A

Explains how the rate of an enzyme-catalysed reaction depends on the concentration of the enzyme and its substrate

36
Q

Define Vmax

A

Max rate of the reaction, all enzyme’s active sites are saturated with substrate

37
Q

Define Km

A

Substrate concentration at which reaction rate is 50% of the Vmax

  • Measure of the affinity an enzyme has for its substrate
  • More lower the value of Km, more efficient the enzyme is
38
Q

3 assumptions of the MMKinetics

A

1) (S) > (E), so the amount of substrate bound by enzyme is negligible

2) (ES) doesn’t change with time

3) Concentration of product is so small, back reaction of P to S is ignored

Rate of formation = Rate of dissociation

39
Q

Equation for V0

A

V0 = Vmax (S) / Km + (S)

40
Q

What does the V0 equation describe?

A

How initial rate of reaction (V) is affected by the initial substrate concentration

41
Q

What do these represent:
1) V0
2) Vmax
3) Km
4) S

A

V0: Initial reaction velocity
Vmax: Maximal velocity of an enzyme catalysed reaction
Km: Michaelis constant
S: Substrate conc

42
Q

Define Kcat

A

No. of substrate molecules converted to product on a single enzyme molecule when it is saturated with substrate

43
Q

Define catalytic efficiency (Kcat/Km)

A

Measure of an enzyme’s specificity for a particular substrate

44
Q
A

Biochemistry (11 decks)

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