1.5 Enzymes

Enzymes

The reaction catalysed by luciferase:

Organisms able to produce their own light using luciferase:

Marine invertebrates

Aequorea victoria - jellyfish Certain clams

Krill

Certain octopuses Colossal Squid

Bioluminescence - Plankton and microbes

Dinoflagellates

Non-marine organisms

Fireflies

Glow worms

Certain centipedes and millipedes

Annelids Mushroom

Bioluminescence - Fish

cookie cutter shark Anglerfish

Key points

• Enzymes are used to control the rate of reactions that occur inside cells - this is known as the

metabolic rate of the cells

• Usually enzymes are involved in making reactions happen more quickly

• All enzymes are made out of protein

• The 3D shape of the enzyme is very important -

Example of an enzyme catalysed reaction:

SUCROSE



Sucrase is the enzyme that catalyses the reaction

• The molecules that enzymes bind to are always referred to as the substrate

• The end products of an enzyme catalyzed reaction are always referred to as the

products.

• In enzyme-catalyzed reactions enzymes

Notice that many enzyme names finish in -ase LUCIFERIN  PRODUCT + LIGHT + HEAT luciferase

HYDROGEN PEROXIDE  WATER + OXYGEN catalase

H₂CO₃  CO₂ + H₂0 carbonic anhydrase

Enzymes may be

intracellular or extracellular

• Intracellular enzymes work inside cells. For example DNA polymerase (used in replication of DNA), the

enzymes that work in respiration or in photosynthesis all stay within the cell.

• Extracellular enzymes are made within cells but excreted outside. For example, the enzymes that

• Spiders and flies secrete an enzyme soup into or on their food. In spiders, this is injected into the prey's body. The enzymes digest the prey's body contents and the spider sucks up the resulting digested food. • Saprophytic fungi also secrete enzymes through their

Activation Energy

• For any reaction a sufficient amount of

energy needs to be given to make the

reaction happen.

• The energy required for a reaction to

happen can be represented by an

• Enzymes reduce the amount of energy

needed to make a reaction happen - they

reduce the activation energy.

• This means that the rate that reactions

occur can increase by up to billion times!

Active site

• This is the part of the enzyme that the substrate binds to

• The active site may involve between 3 and 12 amino acids

• The amino acids that form the active site

come from different positions in the primary structure of the protein

• The primary structure determines 3D folding

• The

types

of amino acids determine types of

bonds e.g. di-sulphide bridge forms between

two cysteine amino acids.

• The

position

of amino acids determines

position of bonds

• The shape of the active site is determined by

position of amino acids

• The shape of active site is complementary

to the substrate

• Globular molecules such as enzymes are

relatively small made up of few amino acids

• Globular proteins having a relatively high

number of small R groups

Two theories of how

enzymes bind to substrate

Lock and key

Two theories of how enzymes

bind to substrate

• Lock and Key

This theory states that the substrate is the exactly

Theory of Induced Fit

• The enzyme molecule wraps around the

substrate and therefore changes shape

• This causes the shape of the substrate

to distort.

• This causes the substrate to be broken

down into products.

http://lysozyme.co.uk/lysozyme-enzyme.php

• Lysozyme is an enzyme used to hydrolyze the bonds in polysaccharides.

• The lysozyme enzyme changes conformation as it binds to the polysaccharide putting a

strain on the internal bonds of the

Factors which affect the rate of

an enzyme controlled reaction

• Temperature

• pH

Temperature

• As the temperature increases the molecules involved in the reaction move faster as they

have more kinetic energy to move around. The substrate molecules and enzyme molecules are more likely to collide, and there will be more

enzyme-substrate complexes. When they do collide this is more likely to result in a reaction. • As the temperature increases the rate of

reaction also increases up to a certain

• If the temperature increases beyond this

temperature, the enzymes molecules

collide with so much energy they start to

break and the precise 3D shape of the

active site (defined by the tertiary

pH

• Enzymes work at their optimum rate at

specific pHs. This is because pH affects the amino acids forming the 3D (tertiary)

structure of the enzyme. The intermolecular bonds that hold the tertiary structure

together are broken down by changes in pH. • If the pH that an enzyme is working at is

Graph effect of substrate

Substrate concentration

• As the substrate concentration increases so does the rate of reaction. This is because as the amount of substrate increases more

enzyme-substrate complexes can be made • As the substrate concentration continues to

rise there comes a point when all of the active sites are already occupied with substrate

molecules. Therefore even when the number of substrate molecules increases, the rate of

Enzyme concentration

• As long as the substrate concentration

remains high, the rate of reaction increases with increasing enzyme concentration.

• This is because as the concentration of enzymes increases there are more active

Inhibitors

• Competitive inhibitors

• Non-competitive inhibitors

Competitive inhibitors

• Very similar shape to the normal substrate • They bind to the active site instead of the

substrate to form an enzyme-inhibitor complex

• This prevents the substrate binding to the enzyme and therefore slow down the rate of reaction as fewer enzyme-substrate

• However at high substrate concentrations the inhibitor has little effect on the rate of

Non-competitive inhibitiors

• The inhibitor does not bind to the active

site but causes the active site to change

shape

• Because the substrate can not bind to

the enzyme this causes the rate of

Non-competitive inhibition

End-product inhibition

• Metabolic reactions within a cell are normally multi-stepped reactions

• The end products may start to build up within the cell. It may be important for the reaction to stop once enough end-product has been made.

• This is achieved by non-competitive inhibition of an enzyme that is involved in one of the

End-product inhibition

A → B → C → D

Design an experiment to find out the

effect of temperature on the following

enzyme controlled reaction

Catalase