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BMS02 > Enzymes & Coenzymes > Flashcards

Enzymes & Coenzymes Flashcards

1
Q

What do enzymes do?

A

(Biological catalysts)

Speed up the rate of a reaction without altering the final equilibrium

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2
Q

What reaction does catalase catalyse? How much faster is the rate of the reaction when catalysed?

A

Hydrogen peroxide to water

10^14 times

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3
Q

What kind of molecule are enzymes?

A

Mainly proteins

Ribosomes = RNA-based

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4
Q

What does an enzyme affect which allows the reaction to occur faster?

A

(Lowers) activation energy

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5
Q

Why does the reaction reach equilibrium with an enzyme?

A

Product has (low) affinity for the enzyme

Product inhibition

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6
Q

What reactions does alcohol dehydrogenase catalyse?

A

Oxidation of primary alcohols to aldehydes

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7
Q

What is the term used to describe when an enzyme can catalyse the reaction of several similar molecules?

A

Group specificity

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8
Q

What will fit in an enzyme’s active site?

A

A substrate with the correct shape and charge

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9
Q

What is an example of a reaction of multiple enzymes acting sequentially on a substrate?

A

D-glucose to lactate/lactic acid

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10
Q

How does the IUB Commission on Enzymes classify enzymes?

A

1-6 based on type of reaction catalysed

4 number code for every individual enzyme

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11
Q

What are the main six classes of enzyme?

A
  1. Oxidoreductases
  2. Transferases
  3. Lyases
  4. Hydrolases
  5. Isomerases
  6. Ligases
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12
Q

What do enzymes of class 1 do?

A

Oxidoreductases

Catalyse redox reactions

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13
Q

Give an example of a class 1 enzyme

A

Lactate dehydrogenase

Anaerobic respiration: pyruvate + NADH + H+ –> L-lactate + NAD+

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14
Q

What do enzymes of class 2 do?

A

Transferases

Catalyse the transfer of functional groups between (different) molecules

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15
Q

Give an example of a class 2 enzyme

A

Alanine aminotransferase

Transamination: glutamate + pyruvate –> L-alanine + a-ketoglutarate

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16
Q

What do enzymes of class 3 do?

A

Lyases

Catalyse the cleavage of C-C, C-O or C-N bonds

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17
Q

Give an example of a class 3 enzyme

A

ATP-citrate lyase

ATP and CoA used in C-C cleavage citrate –> oxaloacetate + acetate

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18
Q

What do enzymes of class 4 do?

A

Hydrolases

Catalyse the cleavage of bonds by the addition of water (often ester bonds)

19
Q

Give an example of a class 4 enzyme

A

Trypsin

20
Q

What do enzymes of class 5 do?

A

Isomerases

Catalyse the transfer of functional groups within the same molecule

21
Q

Give an example of a class 5 enzyme

A

Phosphoglucose isomerase

Glucose-6-phosphate –> fructose-6-phosphate movement of C=O

22
Q

What do enzymes of class 6 do?

A

Ligases

Use ATP to catalyse the formation of new covalent bonds

23
Q

Give an example of a class 6 enzyme

A

DNA ligase

Forms phosphodiester bonds to join 2 segments of DNA

24
Q

What level of protein structure is most important in determining the enzyme’s function?

A

Tertiary

25
Q

What is an enzyme’s thermostability?

A

Range of temperatures within which the enzyme’s structure is maintained (resists irreversible change)

26
Q

What does the Lock and Key model describe?

A

Enzyme’s active site and substrate’s shape are always perfectly complementary to each other

27
Q

What does the modified Lock and Key model describe?

A

Enzyme distorts substrate molecule as active site is not perfectly complementary (increases energy of substrate)

28
Q

What does the Induced Fit model describe?

A

Both the enzyme and substrate change shape on binding to secure substrate and increase its energy (adaptive response)

29
Q

What does chymotrypsin do?

A

Cleaves peptide bonds on carboxyl side of tyrosine, tryptophan, phenylalanine and large hydrophobic residues (eg. methionine)

30
Q

What is the name given to the three amino acids in the active site involved in catalysis?

A

Catalytic triad

31
Q

What amino acids are part of the catalytic triad of chymotrypsins?

A

Serine

Histidine

Aspartic acid

32
Q

What are the two general phases of chymotrypsin catalysis?

A

1: serine nucleophile attacks substrate forming a covalent intermediate bonded to enzyme; first product released (PC)
2: nucleophile created from water attacks covalent intermediate breaking covalent bond to enzyme; second product released (PN)

33
Q

Describe the process of chymotrypsin catalysis

A
  1. Polypeptide substrate binds non-covalently with side chains of hydrophobic pocket
  2. Proton transferred from Ser to His; Ser: attacks C to create a tetrahedral transition state (FIRST TRANSITION STATE)
  3. Proton transferred from His to C-terminal fragment; cleavage of C-N bond and release of PC
  4. Water binds to enzyme in place of PC and transfers proton to His to create OH:-
  5. OH:- attacks carbon of N-terminal fragment creating another tetrahedral transition state (SECOND TRANSITION STATE)
  6. Acyl bond cleaved so PN released; proton transferred back to Ser and enzyme returns to original state
34
Q

What are metalloenzymes?

A

Enzymes that rely on metallic cofactors in order to work (usually transition metals)

35
Q

What is special about flavin enzymes?

A

Iron-sulphur centre

36
Q

What is special about cytochrome oxidase?

A

Haem group

37
Q

What metallic cofactors does cytochrome oxidase have?

A

Cu2+

Fe2/3+

38
Q

What metallic cofactor does pyruvate kinase have?

A

K+

39
Q

Why does pH affect enzymes?

A

Affects protonation of side chains

Affects weak bonds maintaining tertiary structure

40
Q

What are isoenzymes?

A

Enzymes with different protein structures but catalyse the same reaction

41
Q

Where is H4 lactate dehydrogenase found?

A

Heart

42
Q

Where is M4 lactate dehydrogenase found?

A

Muscle

43
Q

What is the structure of lactate dehydrogenase?

A

Four subunits, each of which can be heart or muscle type

44
Q

Which form of lactate dehydrogenase has a lower Km and why?

A

Heart

Lower Km = high affinity for lactate so reaction is faster at lower concentrations of lactate

Do not want lactate to cause muscle cramping in heart

BMS02 (10 decks)

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