1.2- Enzymes

Question 1

What are enzymes?

Answer 1

Proteins that act as biological catalysts

Question 2

What is a catalyst

Answer 2

A substance that increases the rate of reaction without getting used up

(Catalysts are effective in small amounts)

Question 3

Without and with an enzyme how do molecules react

Answer 3

Without they react by randomly colliding
With enzymes they react by the substrate colliding with enough energy to break and form products with an enzyme to create products

Question 4

Metabolism definition

Answer 4

The name for all the chemical reactions occurring in the cells of living organisms

Question 5

Extracellular enzymes def

Answer 5

Enzymes released by the cell

Question 6

Intracellular enzymes def

Answer 6

Enzymes remaining in cell (cytoplasm and plasma membrane)

Question 7

What type of protein are metabolic enzymes and where are they found?

Answer 7

Globular proteins and are made in the cytoplasm

Question 8

Enzymes in catabolic reactions vs anabolic reactions

Answer 8

Catabolic= enzymes break down large insoluble molecules to smaller ones
Anabolic=enzymes build up large molecules from smaller ones

Question 9

Explain the importance of enzymes in activation energy

Answer 9

Enzymes work by lowering the activation energy. In a reaction there is an energy barrier to overcome before the reaction can take place. Substrate molecules have an activation energy which is lowered by enzymes. At the start of the reaction substrates have a certain amount of energy and collide forming an unstable high energy intermediate which quickly forms products. In rearranging the molecules some energy is released so the products have less energy than substrates.

Question 10

Lock and key hypothesis

Answer 10

Enzymes (E) work by binding to their substrate (S) molecule, at the active site on the enzyme.
-The active site is a pocket or crevice on the surface of the enzyme into which the substrate fits.
-This description of the binding of enzyme and substrate is known as the lock and key hypothesis of enzyme
action.
-As the enzyme-substrate complex (ES) forms, the substrate breaks down becoming an enzyme-product
complex (EP) so that the products (P) no longer fit the active site and are released leaving the unchanged enzyme

Question 11

The induced fit hypothesis:

Answer 11

Like lock and key hypothesis only the active site moulds itself to be complementary to the substrate in shape and once the substrate is fitted in the substrate is broken down and releases products

Question 12

Lock and key hypothesis features (6)

Answer 12

Enzymes have a specific three-dimensional shape.

The active site fits exactly the substrate molecule’s shape i.e. it is complimentary.

The two molecules form the temporary enzyme-substrate complex.

The reaction takes place at the active site and the products are formed.

Since the products have a different shape from the substrate, they no longer fit the active site and are
repelled.

-The active site is then free to interact with another substrate molecule.

Question 13

The induced fit hypothesis features (5)

Answer 13

 The active site has a more flexible shape.

 As the substrate begins to bind the active site changes shape and is able to mould itself around the substrate.

 As the enzyme changes shape, it puts pressure on the substrate, breaking particular bonds, and therefore
lowering the activation energy and allowing the reaction to take place.

 It is only when it binds closely to the substrate that the active site catalyses the reaction and the products are released (as they have a different shape to the substrate).

 The active site returns to its “pre-reaction” shape.

Question 14

Explain what Co-factors are

Answer 14

 All enzymes are proteins, but not all enzymes are made of protein only.
 Most enzymes are Conjugated proteins and have an important non-protein part attached to the protein.
 The non-protein part is called a cofactor. It normally forms part of the active site and is essential for the
enzyme to function properly.
 Cofactors function either by influencing the shape of an enzyme (to its optimum for substrate attachment) or
by participating in the enzyme-catalysed reaction (by attaching to one of the products for transfer to another
enzyme).

Question 15

What are the two types of co-factors

Answer 15

Prosthetic groups and Coenzymes

Question 16

Explain what a prosthetic group is

Answer 16

These are non-protein, organic molecules that contain a metal ion
e.g. Fe, Mg, Zn.
They form a permanent attachment to the enzyme. eg, the iron-containing haem group, is also a prosthetic group in the enzyme
catalase.

Question 17

Explain what a Co-Enzyme is

Answer 17

These are small non-protein, organic molecules that are not permanently
attached to the enzyme.
Their function is to help the enzyme and substrate to bind with each other. e.g.
NAD & FAD are important coenzymes which act as hydrogen acceptors in
respiration.
Many coenzymes are derived from vitamins.

Question 18

How does temperature effect enzymes

Answer 18

Increasing the temperature increases the rate of most chemical reactions because the molecules have more
kinetic energy and move around more quickly.
 There is a greater chance of collisions between enzymes and substrates. Therefore more enzyme-substrate
complexes are formed and hence the rate of reaction increases.

There is a sharp decline in enzyme activity beyond the optimum temperature. The increase in temperature
causes the atoms in the enzyme molecule to vibrate more. Beyond the optimum temperature, this vibration
causes hydrogen bonds to break along with other bonds that help to keep the molecule in its three-dimensional structure.

 This causes the active site to lose its complementary shape for substrate attachment. The enzyme is described
as being denatured.
pH

Question 19

How pH effects enzymes

Answer 19

Enzymes have an optimum pH at which the rate of reaction is fastest.

Any deviation from the optimum pH may cause a decrease in enzyme activity.

 A change in pH may disrupt ionic bonds in the tertiary
structure. This means that the 3-D shape of the active site is altered. The further the pH is from optimal, the greater the degree of disruption to the bonds.

 The enzyme is described as being denatured. Therefore at non-optimal pH, the substrate attaches less readily
to the enzyme and hence the rate of reaction decreases.

 However these effects are reversible for small changes in pH. When the pH reverts to the enzyme’s optimum,
the active site reforms to normal.

Question 20

Factors effecting enzyme reactions

Answer 20

1. Temperature
2. pH
3. Substrate concentration
4. Enzyme concentration

Question 21

How substrate concentration effects enzymes

Answer 21

 At lower concentrations of substrate the rate increases in direct proportion to the substrate concentration i.e.
enzyme activity increases as substrate concentration increases.

 This is because a greater concentration of substrate molecules increases the chances of collision with enzyme molecules. Therefore it is more likely that a substrate molecule will bind to an empty active site and form an enzyme-substrate complex.

 At higher concentrations of substrate the rate of reaction becomes constant.

 At these high concentrations there is more substrate present than enzyme.
Therefore all the active sites are
occupied (saturated) and the substrate molecules have to ‘queue up’ to bind to them.

Question 22

How enzyme concentration effects the reaction

Answer 22

Provided conditions such as temperature and pH are suitable and there is an excess of substrate, then the rate of reaction will be directly proportional to the enzyme concentration i.e. an increase in enzyme concentration will increase the rate of reaction.

This is because an increase in the concentration of enzyme molecules increases the chance of successful collisions with substrate molecules.

At high enzyme concentration the activity may level off, but only if there is insufficient substrate.

As it is often the number of enzymes and not substrates that limits reactions in living organisms, there are many
adaptations to increase enzyme number.

The extensive infolding of the mitochondrial cristae increase the surface
area of the inner membrane, and therefore the number of respiratory enzymes located on the membrane.

Question 23

Explain what Competitive inhibition is

Answer 23

 Competitive inhibitors are a molecule that is similar in shape to the substrate molecule

 The inhibitor competes with the substrate for the active site of the enzyme molecule.

 The inhibitor’s shape allows it to fit into the active site, preventing the substrate from fitting in and thus preventing the formation of an enzyme -substrate complex.

 The rate of reaction is therefore reduced.

 The competitive inhibitor does not remain in the active site permanently and so its effect is temporary.

 If the inhibitor is removed the active sites will all be free to combine with substrate molecules.

 The degree of inhibition depends on the concentration of the inhibitor and the substrate because each is competing for a place on the active site.

 Increasing the concentration of the substrate will decrease the effect of the inhibitor because it is more likely
that a substrate molecule will bind to an active site.

Question 24

Explain what non-competitive inhibition is

Answer 24

A non-competitive inhibitor does not bind to the active site of the enzyme but attaches to some other part of the enzyme molecule.

 This alters the overall shape of the enzyme molecule including the active site, so it is no longer complementary to the shape of the enzyme. The substrate can no longer bind with the active site.

 Since the substrate and inhibitor are not competing for the active site, increasing the concentration of the substrate will not reduce the effect of the inhibitor, as the number of functioning enzymes has been reduced.

 These enzymes are called allosteric enzymes, as they have a second site where non-enzyme molecules can
bind.

Question 25

Explain what Elastase is

Answer 25

Elastase Is an enzyme released by white blood cells as a consequence of lung infection.

 breaks down bacterial pathogens and is part of the immune response.

 Breaks down the protein elastin, which contributes to the elasticity of the alveoli – it assists with the stretch & recoil of the lung tissue.

Normally elastin is not broken down as the elastase inhibitor; alpha-1-antitrypsin
(A1AT) prevents elastase activity after the infection has been cleared.

 Cigarette smoke inhibits the synthesis of A1AT, resulting in too much elastin being released in the lung tissue,
as there is not enough A1AT to effectively control elastase. The elastin is broken down resulting in elastase-induced emphysema.

Question 26

How do enzyme inhibitors work as therapeutic drugs

Answer 26

Enzymes are involved in disease progression either directly eg elastase, or by controlling integral metabolic pathways in pathogenic microorganisms. If enzyme inhibitors are used to target enzymes involved in causing
disease, then disease progression can be reduced or even stopped.

For enzyme inhibitors to be effective in this role, they need to be:
 Specific – they will only target the enzyme involved in disease progression
 Able to work well at low doses. This prevents a build up of inhibitor, as high levels may be toxic.

Current research includes working out the shape of the active site of some enzymes involved in disease progression through modelling, and developing inhibitors with a complementary shape top block their active
sites.

Question 27

Examples of enzymes involved in therapeutic drugs (5)

Answer 27

 A1AT used to medically reduce the harmful effects arising from lung infection

 ACE (Angiotensin Converting Enzyme) inhibitors can be used to treat high blood pressure and other
cardiovascular conditions. They inhibit an enzyme that normally constricts blood vessels (causing increased blood pressure). The ACE inhibitors reduce the constriction of blood vessels and consequently lower blood pressure.

 Penicillin (and some other antibiotics) inhibits the enzymes involved in cell wall formation in bacteria.

 Some antiviral drugs inhibit the DNA/RNA polymerases that are essential in viral replication.

 Some cancer treatments involve enzyme inhibitors.

Question 28

Immobilised enzyme definition

Answer 28

An immobilised enzyme is one that has been physically or chemically attached onto or inside an inert, insoluble
material.

Question 29

3 advantages and 2 disadvantages to immobilised enzymes in the method of Adsorption

Answer 29

 The enzyme is held by weak forces on the surface of an inert material e.g. glass,
alginate beads or matrix.

 It is easy for the enzyme to come in contact with the substrate as there is no barrier.

 This process is relatively straightforward and inexpensive.

 It is not always reliable as the enzymes can be washed from the absorptive material

 Some of the enzyme sites may be inaccessible as some of the enzyme is attached to
the glass

Question 30

Method of immobilising enzymes: Cross linkages, explain this method

Answer 30

 The enzymes form covalent bonds with a matrix eg cellulose.

 Cross-linking can damage some enzymes but those that are not damaged
remain very active as reactants have easy access.

Question 31

Explain the immobilised enzyme method of entrapment

Answer 31

The enzyme molecules are trapped in the spaces within a polymer. They are
between the fibres of a gel or else held securely inside insoluble beads or
microspheres, for example, calcium (or sodium) alginate beads.

In both cases the enzymes are not chemically attached but the substrate
molecules and product must be small enough to diffuse freely in and out the
matrix or pores.

Question 32

Explain the method of Encapsulation

Answer 32

The enzymes are trapped inside a selectively permeable membrane such as
nylon.

 The gels or materials involved in some types of immobilisation may reduce
the speed of diffusion between the substrate and the enzyme.

 Immobilisation also holds some enzymes in physical positions that make some
of the enzyme sites inaccessible.
Once the enzymes have been immobilised they are packed into a column through which a supply of the substrate is continually flows through to form the product. This ensures maximum production.

Rates of flow; method of immobilisation and environmental conditions can
be controlled to ensure maximum efficiency.
The flow rate through the column influences activity.
If it is too slow the reaction is completed early in the column;
If too fast and not all the substrate will have been engaged in the reaction.

Question 33

Advantages of the immobilised enzyme (5)

Answer 33

 The enzyme can be used over and over again.

 The product is enzyme-free (not contaminated) i.e. there is no
purification process required to separate the product from the enzyme.

 It facilitates a continuous flow process e.g. removal of lactose from milk.

 The enzyme may be much more stable and long-lasting since it is
protected by the inert matrix.

 it remains active over a greater temperature (thermostability) and pH
range than if the enzyme were in solution.

Question 34

Disadvantages of using an immobilised enzyme (2)

Answer 34

 There may be reduced enzyme activity due to inaccessibility of some of
the active sites i.e. the active site may be facing the supporting matrix
and therefore are inaccessible for the substrate molecules to fit into.

 The active site may be altered during the binding process.

Question 35

Biosensor definition

Answer 35

A biosensor is an electronic device that is used to carry out a diagnostic test such as monitoring glucose in the
blood.

Question 36

How is clinistix used to diagnose

Answer 36

this is an example of a diagnostic reagent strip used as a biosensor to measure glucose in urine samples

 The test strips contain two immobilised enzymes, glucose oxidase and peroxidise, and a colourless hydrogen
donor compound.

 The strip is dipped into a urine sample. If glucose is present, a colour change will occur as a result of the reactions catalysed by the enzymes. The more glucose present, the more densely coloured dye is produced. The colour of the test strip is then compared with a printed scale to indicate the amount of glucose in the urine.

Question 37

How are enzyme inhibitors used to diagnose

Answer 37

The inhibitor is attached, and the enzyme being monitored is captured by its active site on the diagnostic strip to give a positive read out. This is used in early identification of some cardiovascular diseases and pre-eclampsia.

Question 38

(Damaging) ACE enzyme-> Disease+Function of enzyme+inhibitor + notes

Answer 38

-Heart disease

-Converts angiotensin 1–> angiotensin 2 which contributes to the vasoconstriction of arteries and increased blood pressure

-the inhibitor= ACE inhibitor

-ACE is apart of the normal blood pressure regulating mechanism

Question 39

(Damaging enzyme) Elastase->
Disease+Function of enzyme+inhibitor + notes

Answer 39

-Respiratory disease

-Hydrolyse elastin in alveolar walls

-Elastase inhibitors + antitrypsin

-Elastase is produced by white blood cells and helps them move through tissues to the infection site