Eduquas A level Biology Core concepts Enzymes

structure and function of enzymes

globular proteins (Quaternary structure)

catalyse biological reactions by lowering activation energy

enzyme structure

specific 3D shape with active site complementary to specific substrate

if shape of allosteric site changes, active site shape also changes

Lock and Key

Active site does not change

Induced fit

specific but not rigid active site

anabolic reaction

build up

synthesis, polymerisation

catabolic

break down

digestion, hydrolysis

Factors affecting enzyme action

Temperature

pH

Substrate concentration

Enzyme concentration

Enzyme inhibition

how temperature affects enzymes

as temperature increases, rate of reaction increases, until maximum rate of reaction is reached, from then on increasing temperature decreases rate of reaction

- at low temp, less Ek, so molecules move less, less collisions = decreased rate of reaction

- increasing temp, increases Ek, move movements, more successful collisions = more enzyme substrate complexes per unit time = increased rate of reaction

-at OPTIMUM TEMP, molecules move at max velocity = max rate of reaction

- if temperature continues to increase, molecules vibrate, breaking weaker hydrogen bonds in tertiary structure, enzyme shape changes so active site shape changes and is no longer complementary to specific substrate

Optimum temperature defintion

temperature at which rate of reaction is at its maximum

denature defintion

molecules in enzyme vibrate, breaking weaker hydrogen bonds in tertiary structure, enzyme shape changes so active site shape changes and is no longer complementary to specific substrate

how pH affects enzyme action

change from optimum pH cause decrease in rate of reaction

- small change inactivates enzymes

- big change - enzymes denaturing

how substrate concentration affects enzyme action

as concentration increases, rate if reaction increases, until x, when increasing concentration does not affect rate of reaction

substrate concentration is limiting factor

how enzyme concentration affects enzyme action

as concentration increases, rate if reaction increases, until x, when increasing concentration does not affect rate of reaction

enzyme concentration becomes limiting factor

how enzyme inhibition affects enzyme action

Competitive - eg malonate

-compete with substrate for active site

- forms enzyme-inhibitor complex - so substrate cannot bind --> decreasing rate of reaction

- counteract by increasing substrate concentration

Non competitive - eg Potassium cyanide

- binds with allosteric site, causing change in shape of allosteric site and change in shape of active site

- active site in no longer complementary to specific substrate = rate of reaction decreases

- cannot be overcome by increasing substrate concentration

Biosensors function

rapid detection of metabolites

contain enzymes

Simple biosensors

qualitative - on/off

dye

diagnostic tool

Digital biosensors

quantitative - data

very accurate - even at low temp

monitoring tool

convert chemical energy into electric impulse

Immobilised enzymes structure

fitted into inert solid matrix

Entrapment

enzymes in gel membrane

eg silica gel, collagen fibres

Micro encapsulation

enzymes trapped in semi=permeable membrane

eg alginate beads (large surface area)

Advantages of immobilised enzymes

1. inert solid matrix creates physical barrier

- enzymes are more stable at higher temperatures

- work at larger range of pHs

- therefore, several enzymes with different optimums can be used at the same time

2. product not contaminated by enzyme

3. enzyme can be recovered/reused

4. continuous process

disadvantages of immobilised enzymes

1. reduces movement

- decreased activity

2. expensive