Enzymes

Question 1

What are enzymes

Answer 1

A catalyst speeds up the rate of a
chemical reaction but is not
used up during the course
of the reaction
Most enzymes are globular proteins, with only a few being
RNAs.
Enzyme names commonly end with “-ase

Question 2

Biochemical Roles

Answer 2

 Digest macromolecules.
 Construct macromolecules to build cells, tissues, and
organs.
 Breakdown harmful waste products from metabolism.
and…
 Send messages around cells

Question 3

Endergonic Reaction

Answer 3

If a reaction requires to take in energy and as such, CANNOT
happen spontaneously, it is called an ‘endergonic reaction’
 Absorbs energy
 Not spontaneous reaction

the energy within the system is increased
Endergonic reaction
example:
Photosynthesis

Question 4

Exergonic Reaction

Answer 4

If a reaction releases energy and happens spontaneously, it is
called an ‘exergonic reaction’
 Releases energy
 Spontaneous reaction

the energy within the system is decreased
Glucose breakdown is a
catabolic reaction –
breakdown
net release of energy.

Question 5

Anabolic

Answer 5

create a product out of
smaller reactants

Question 6

Catabolic

Answer 6

break down larger reactants
into smaller products

Question 7

AE

Answer 7

 In ALL chemical reactions the initial stable state must become
less stable before a reaction can start.
 This is why both exergonic and endergonic reactions need to be
provided with energy before they will proceed.
 The minimum amount of energy required to initiate a
chemical reaction.
 This energy is needed to destabilise the reactants so
they are ready to form new chemical bonds.
 These destabilised reactants are called transition-state
intermediates.
 Enzymes work by lowering the
activation energy of a reaction

Question 8

Coupled Reaction

Answer 8

Exergonic reactions and endergonic reactions are often
coupled.
Exergonic reactions fuel (provide energy for) endergonic
reactions in cells

Question 9

Subsequent numbers after the main code (EC1, EC2, etc…)
represent a progressively finer classification of the enzyme

Answer 9

Example: the tripeptide aminopeptidases have the code “EC 3.4.11.4“.
EC 3 enzymes are hydrolases (enzymes that use water to break up
some other molecule)
EC 3.4 are hydrolases that act on peptide bonds
EC 3.4.11 are those hydrolases that cleave off the amino-terminal
amino acid from a polypeptide
EC 3.4.11.4 are those that cleave off the amino-terminal end from a
tripeptide
TO CLARIFY THE CLASSIFICATION METHOD – INFORMATION ON THIS SLIDE WILL NOT BE ASSESED.

Question 10

EC1 - OXIDOREDUCTASES

Answer 10

Transfer electrons from one molecule to another molecule.
REDOX reactions
Reduction - Oxidation (Redox) reactions
 Redox reactions involve the transfer of electrons.
 Atoms, ions or molecules that lose an electron have been
oxidised.
 Atoms, ions or molecules gaining electrons have been
reduced.

Question 11

OIL RIG

Answer 11

Oxidation is losing electrons
Reduction is gaining electrons

Question 12

Reduction Example
(RIG)

Answer 12

Mg2+ + 2e- ——>Mg
Decreased.
Net charge is
reduced.

Question 13

Oxidation Reaction
(OIL)

Answer 13

Mg -2e- ——-> Mg2+
Increase in Net Charge

Question 14

EC2 - TRANSFERASES

Answer 14

Transfer a functional group from one molecule to another.
aminotransferases move amino (NH2) groups,
methyltransferases move methyl (CH3) groups

Question 15

EC3 - HYDROLASES

Answer 15

Break bonds using water (in hydrolysis reactions).
AB + H2O A-OH + B-H
Example= serine hydrolases (proteases – break peptide bonds)
erine’ in the enzyme’s name means
that the enzyme contains a serine in its active site.
(It is not related to its target amino acid sequence)

Question 16

EC4-Lyase

Answer 16

 Non-hydrolytic addition of groups to substrates, or
 Non-hydrolytic removal of groups from substrates.
 Uses these bonds: C-C, C-O, C-N or C-S
 Usually ends up forming double bonds and ring structures.

Question 17

EC5-Isomerases

Answer 17

Convert a molecule from one isomer to another
phosphoglucoseisomerase
glucose-6-phosphate ———> fructose-6-phosphate

Question 18

EC6-Ligase

Answer 18

Use energy from ATP to join one molecule to another.
Also known as synthetases
e.g DNA ligase

Question 19

EC7 - Translocases

Answer 19

Catalyze the movement of ions or molecules across
membranes or their separation within membranes

Question 20

Globular Structure

Answer 20

Protein structure is flexible, so it changes when other
molecules bind.
 This means
enzymes can be
used as switches
that change from
inactive to active
and active to
inactive state.

Question 21

Carbonic Anhydrase

Answer 21

Converts CO2 to soluble molecules in the blood to be transported
to the lungs.
 Assists the conversion of CO2 to carbonic acid, which is then
converted to bicarbonate and hydrogen.
CO2 + H2O H→ 2CO3 HCO→ 3 + H+
Without enzyme —– 200 molecules of CO2 is processed/hour
With enzyme —– 600,000 molecules/second

Question 22

Active Site

Answer 22

The region on an enzyme where the substrate
binds.
 Takes up a very small part of the whole structure of the
enzyme

Active sites are unique biochemical environments where the amino
acids must have the correct functional groups to participate in
chemical reactions.
 The amino acids that form the active site and participate in the
making and breaking of bonds are called catalytic sites.
 Binding in the active site may involve hydrogen bonding,
electrostatic/hydrophobic interactions and temporary covalent bonds.
 Enzymes only catalyse substrates that have a complementary 3D
shape to the active site.
 Changes to the shape of the enzyme will change the shape of the
active site and the substrate will be unable to bind
 The amino acids that form the active site are often located very
far apart in the protein’s primary sequence

Question 23

For enzymes to be active they often require helper
molecules called cofactors

Answer 23

Types of cofactors
 Metal ions are used as cofactors by 1/3rd of
enzymes – commonly iron, copper, or zinc.
 Coenzymes are often also used – coenzyme
A, NAD, ATP.
 Prosthetic groups are non-protein, organic
molecules that help with enzyme function,
e.g. haem and retinal

Example cofactor 1: Haem (or heme)
 Haem (or heme) is an organic
molecule with a central iron atom.
 Peroxidases are examples of
enzymes with haem co-factors.
 These break down hydrogen
peroxide (H2O2) produced in
respiration.

Question 24

An enzyme may catalyse both directions in reversible
reactions

Answer 24

The enzyme remains unchanged after creating products at either end of the reversible reaction

Question 25

Enzyme Concentration

Answer 25

 More enzyme means more
active sites…
 More number of available
active sites means increased
reaction rate.

Question 26

Substrate Concentration

Answer 26

 The reaction rate increases
because there is more
substrate available to catalyse.
 The rate stops increasing
because if there is a fixed
amount of enzyme all the
active sites become occupied

Question 27

Temperature

Answer 27

 Most human enzymes have an optimal
temperature (≈37.5°C).
 With increasing temperature, the enzymes
and substrates are moving faster so are
more likely to interact.
 When temperature is too high this
denatures the enzyme. The enzyme’s
secondary & tertiary structure is
damaged so the active site loses its shape
and cannot bind to substrate

Question 28

pH

Answer 28

 Different enzymes have different
optimal pHs, e.g. pepsin in the stomach
requires pH of 1.5 whereas trypsin in
the small intestine works best at pH 8.
 Enzymes that use ionic bonds between
active site and substrate may be
affected by a different pH.

Question 29

Presence of inhibitors or activators

Answer 29

 Enzyme inhibition can be reversible or irreversible
 Irreversible inhibitors dissociate very slowly from the
enzyme because they bind with covalent bonds.
 Many drugs are irreversible enzyme inhibitors:
e.g. Penicillin and aspirin

Question 30

Phenylketonuria (PKU)

Answer 30

• Autosomal recessive condition affecting 1/10,000 people.
• Non-functioning phenylalanine hydroxylase (PAH; 1.14.16.1);
  over 500 known mutations; most found in the catalytic
  domain.
• Symptoms: mainly damage to brain and nervous system
  causing learning difficulties; behavioural difficulties;
  epilepsy.
• Treatment is a change in diet to reduce intake of
  phenylalanine

Question 31

Tay-Sachs disease

Answer 31

• Part of a group of diseases called lysosomal storage diseases.
• Rare autosomal recessive disease.
• Non-functioning hexosaminidase-A (HexA; 3.2.1.52). Over 80
  known mutations.
• Enzyme should break down gangliosides in neurons.
• Appears in early infancy when development slows. Symptoms
  include seizures, loss of hearing and vision, paralysis and
  intellectual disability. Severe form is fatal in childhood