Biology IB HL - 2.5 Enzymes

An enzyme is a globular protein which acts as a biological catalyst by speeding up the rate of a chemical reaction

No

Enzymes are not changed or consumed by the reactions they catalyse and thus can be reused

Enzymes are typically named after the molecules they react with (called the substrate) and end with the suffix ‘-ase’

For example, lipids are broken down by the enzyme lipase

The active site is the region on the surface of the enzyme which binds to the substrate molecule

The active site and the substrate complement each other in terms of both shape and chemical properties

Hence only a specific substrate is capable of binding to a particular enzyme’s active site

Enzyme reactions typically occur in aqueous solutions (e.g. cytoplasm, interstitial fluid, etc.)

Consequently, the substrate and enzyme are usually moving randomly within the solution (Brownian motion)

Sometimes an enzyme may be fixed in position (e.g. membrane-bound) – this serves to localise reactions to particular sites

Enzyme catalysis requires that the substrate be brought into close physical proximity with the active site

When a substrate binds to the enzyme’s active site, an enzyme-substrate complex is formed

The enzyme catalyses the conversion of the substrate into product, creating an enzyme-product complex

The enzyme and product then dissociate – as the enzyme was not consumed, it can continue to catalyse further reactions

Increasing the molecular motion of the particles (thermal energy can be introduced to increase kinetic energy)

Increasing the concentration of particles (either substrate or enzyme concentrations)

The shape and chemical properties of the active site are highly dependent on the tertiary structure of the enzyme

Yes

Like all proteins, enzyme structure can be modified by external factors such as high temperatures and extreme pH

These factors disrupt the chemical bonds which are necessary to maintain the tertiary structure of the enzyme

Any change to the structure of the active site (denaturation) will negatively affect the enzyme’s capacity to bind the substrate

Various factors may affect the activity of enzymes, by either affecting the frequency of enzyme-substrate collisions or by affecting the capacity for the enzyme and substrate to interact (e.g. denaturation)

Temperature, pH and substrate concentration will all influence the rate of activity of an enzyme

Low temperatures result in insufficient thermal energy for the activation of an enzyme-catalysed reaction to proceed

Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity

This is because a higher kinetic energy will result in more frequent collisions between the enzymes and substrates

At an optimal temperature (may vary for different enzymes), the rate of enzyme activity will be at its peak

Higher temperatures will cause enzyme stability to decrease, as the thermal energy disrupts the enzyme’s hydrogen bonds

This causes the enzyme (particularly the active site) to lose its shape, resulting in the loss of activity (denaturation)

Changing the pH will alter the charge of the enzyme, which in turn will alter protein solubility and overall shape

Changing the shape or charge of the active site will diminish its ability to bind the substrate, abrogating enzyme function

Enzymes have an optimal pH (may differ between enzymes) and moving outside this range diminishes enzyme activity

Increasing substrate concentration will increase the activity of a corresponding enzyme

More substrates mean there is an increased chance of enzyme and substrate colliding and reacting within a given period

ONLY INITIALLY

| After a certain point, the rate of activity will cease to rise regardless of any further increases in substrate levels

This is because the environment is saturated with substrate and all enzymes are bound and reacting (Vmax)

Which factor to investigate (i.e. the independent variable)

Which enzyme / substrate reaction to use

How to measure the enzyme activity (i.e. the dependent variable

Temperature (use water baths to minimise fluctuations)

pH (acidic or alkaline solutions)

Substrate concentration (choose range to avoid saturation)

Presence of inhibitor (type of inhibitor will be enzyme-specific)

The amount / rate of substrate decomposition (e.g. breakdown of starch)

The amount / rate of product formation (e.g. formation of maltose)

immobilised enzymes have been fixed to a static surface in order to improve the efficiency of the catalysed reaction

Enzyme concentrations are conserved as the enzyme is not dissolved – hence it can be retained for reuse

Separation of the product is more easily achieved as the enzyme remains attached to the static surface

biofuels

medicine

biotechnology

food production

textiles

paper

Enzymes are used to breakdown carbohydrates to produce ethanol-based fuels

Enzymes are used to identify a range of conditions, including certain diseases and pregnancy

Enzymes are involved in a number of processes, including gene splicing

Enzymes are used in the production and refinement of beers and dairy products

Enzymes are utilised in the processing of fibres (e.g. polishing cloth)

– Enzymes assist in the pulping of wood for paper production

Lactose is a disaccharide of glucose and galactose which can be broken down by the enzyme lactase

Historically, mammals exhibit a marked decrease in lactase production after weaning, leading to lactose intolerance

Incidence of lactose intolerance is particularly high in Asian, African and Aboriginal populations

Incidence is lower in European populations (due to a mutation that maintains lactase production into adulthood)

Lactose-free milk can be produced by treating the milk with the enzyme lactase

The lactase is purified from yeast or bacteria and then bound to an inert substance (such as alginate beads)

Milk is then repeatedly passed over this immobilised enzyme, becoming lactose-free

Scientists are currently attempting to create transgenic cows that produce lactose-free milk

This involves splicing the lactase gene into the cow’s genome so that the lactose is broken down prior to milking

As a source of dairy for lactose-intolerant individuals

As a means of increasing sweetness in the absence of artificial sweeteners

As a way of reducing the crystallisation of ice-creams

As a means of reducing production time for cheeses and yogurts

broken down into glucose and galactose - monosaccharides are sweeter tasting

monosaccharides are more soluble, less likely to crystalise

bacteria ferment monosaccharides more readily