EnzymesEnzymes

Aims:Aims:

Must be able to outline the role of enzymes.Must be able to outline the role of enzymes.

Should be able to describe how the process Should be able to describe how the process happens.happens.

Could be able to explain factors affecting Could be able to explain factors affecting enzyme function.enzyme function.

EnzymesEnzymes

Globular proteins with an active site capable of acting as Globular proteins with an active site capable of acting as catalysts.catalysts.

Therefore tertiary structure most important to function.Therefore tertiary structure most important to function.

Therefore any change to tertiary structure will result in a Therefore any change to tertiary structure will result in a loss of catalytic function.loss of catalytic function.

Many proteins require other factors to aid function:Many proteins require other factors to aid function:– COFACTOR – metallic ions e.g. copper, zinc, ironCOFACTOR – metallic ions e.g. copper, zinc, iron– CO-ENZYME – organic molecule e.g. vitamin, NADCO-ENZYME – organic molecule e.g. vitamin, NAD– Some co-enzymes are permanently attached – PROSTHETIC Some co-enzymes are permanently attached – PROSTHETIC

GROUP.GROUP.

Enzyme ActionEnzyme Action

Act by lowering ACTIVATION ENERGY required for Act by lowering ACTIVATION ENERGY required for chemical reaction to take place.chemical reaction to take place.

Graph:Graph:

Enzyme present = less energy required.Enzyme present = less energy required.

Reaction takes place more readily.Reaction takes place more readily.

Increased speed of reaction (do not alter equilibrium Increased speed of reaction (do not alter equilibrium constants).constants).

Enzyme ActionEnzyme Action

1.1. Enzyme binds to it’s substrate forming an Enzyme binds to it’s substrate forming an ENZYME/SUBSTRATE complex.ENZYME/SUBSTRATE complex.

2.2. Reaction takes place and product(s) formed.Reaction takes place and product(s) formed.

3.3. Enzymes emerge unchanged.Enzymes emerge unchanged.

4.4. Enzymes can be reused.Enzymes can be reused.

5.5. Therefore enzymes are effective in minute Therefore enzymes are effective in minute concentrations.concentrations.

Theories of Enzyme ActionTheories of Enzyme Action

LOCK AND KEYLOCK AND KEY

Enzyme has an active Enzyme has an active site and the substrate(s) site and the substrate(s) fits the site.fits the site.

Reaction takes place, Reaction takes place, substrate(s) releasedsubstrate(s) released

INDUCED FITINDUCED FIT

Substrate(s) bind to active Substrate(s) bind to active site, inducing a change in site, inducing a change in the enzyme so the the enzyme so the substrate(s) fit more easily.substrate(s) fit more easily.

When closely bound, When closely bound, reaction takes place.reaction takes place.

Substrate(s) released, Substrate(s) released, enzyme returns to original enzyme returns to original shape.shape.

Factors Affecting RateFactors Affecting Rate

SUBSTRATE SUBSTRATE CONCENTRATION:CONCENTRATION:

Increased concentration = Increased concentration = increased rate – increased increased rate – increased chance of collisionschance of collisions

Levels off at a given pointLevels off at a given point

V-max = maximum rate of V-max = maximum rate of reaction – All active sites reaction – All active sites occupied.occupied.

Graph:Graph:

ENZYME ENZYME CONCENTRATION:CONCENTRATION:

Increased concentration = Increased concentration = increased rate – more active increased rate – more active sites available.sites available.

Substrate concentration must Substrate concentration must be in excess of enzyme.be in excess of enzyme.

pHpH

Enzymes have an optimum pH for maximum velocity.Enzymes have an optimum pH for maximum velocity.

Graph:Graph:

Small changes in pH alter H-bonds and ionic attractions = small Small changes in pH alter H-bonds and ionic attractions = small loss of catalytic activity = decrease in reaction rate (reversible).loss of catalytic activity = decrease in reaction rate (reversible).

Larger changes break disulphide bonds and even hydrolyse Larger changes break disulphide bonds and even hydrolyse peptide bond – loss of 3D shape – denaturation – loss of catalytic peptide bond – loss of 3D shape – denaturation – loss of catalytic function (Not reversible).function (Not reversible).

pH changes can lead to a change in charge distribution = loss of pH changes can lead to a change in charge distribution = loss of attraction between enzyme and substrate:attraction between enzyme and substrate:

Diagram:Diagram:

TemperatureTemperature

Graph:Graph:

0-400-40°°C = increasing temperature = increasing C = increasing temperature = increasing rate of reaction – increased speed of substrate rate of reaction – increased speed of substrate and enzyme movement = increased chance of and enzyme movement = increased chance of collision.collision.

40-6040-60°°C = increasing temperature = decrease C = increasing temperature = decrease rate of reaction – atoms vibrate breaking bonds rate of reaction – atoms vibrate breaking bonds = denaturation and loss of catalytic function.= denaturation and loss of catalytic function.

Inhibitors Inhibitors

Chemicals that interfere with enzyme functions:Chemicals that interfere with enzyme functions:

COMPETITIVE – Compete with substrate for COMPETITIVE – Compete with substrate for active site of enzyme – can bind permanently active site of enzyme – can bind permanently with enzyme.with enzyme.

NON-COMPETITIVE – bind to part of enzyme NON-COMPETITIVE – bind to part of enzyme (not active site) – prevent/reduce enzyme (not active site) – prevent/reduce enzyme function.function.

ActivityActivity

Answer the questions from pages 35 to 40 Answer the questions from pages 35 to 40 in Biozone book.in Biozone book.