Topic 3: Enzymes

define enzyme

biological catalysts that increase the rate of reaction and are not chemically altered in the process. made out of globular proteins

properties of enzymes

1. globular proteins

2. specific due to conformation at active site

3. effective in small amounts

4. remain chemically unchanged at the end of reaction

5. lowers activation energy of reaction

6. extremely efficient

7. biological catalysts

definition of activation energy

energy required to make substances react

why are enzymes helpful in terms of activation energy

• the larger the activation energy, the slower the reaction

• enzymes lower activation energy which makes reaction faster

what are the two hypotheses used to describe enzyme action

1. LOCK AND KEY HYPOTHESIS

2. INDUCED FIT HYPOTHESIS

describe the lock and key hypothesis

1. active site has a specific shape to which the substrate binds

2. substrate (key) is complementary to and fits exactly into shape of active site (lock) which forms an enzyme-substrate complex

3. once reaction is completed, the products no longer fit into active site and are released. active site is now free to receive new substrates

describe the induced fit hypothesis

1. some enzymes and their active sites are physically flexible

2. shape of substrate complementary to active site but not exact fit

3. binding of substrate to active site induces a small conformational change in enzyme shape

4. enables substrate to fit more snugly in the active site, forming enzyme-substrate complex

5. once reaction is completed, the products no longer fit into active site and are released. active site is now free to receive new substrates

how enzymes work

1. substrate and enzyme collide at correct orientation

2. substrate binds to enzyme at active site, forming a short-lived enzyme-substrate complex.

3. chances of reaction occuring is greatly enhanced

4. reaction occurs

5. once reaction is completed, the products no longer fit into active site and are released. active site is now free to receive new substrates. enzyme is chemically unchanged and can be reused

what are the factors affecting rate of enzyme action

1. temperature

2. pH

3. substrate concentration

4. enzyme concentration

how TEMPERATURE affects rate of enzyme action

1. increase in temperature → increase in kinetic energy of enzyme and substrate molecules

2. increase in effective collisions → more enzyme-substrate complexes formed per unit time

3. rate of reaction increases with temperature until optimum temperature of 30℃-40℃ (enzyme functions at max rate) is reached

4. increase beyond optimum temp → denatured enzyme → rate of enzyme action decreases

what happens when enzyme is denatured

1. enzymes are made out of proteins. excessive heat disrupts the intermolecular bonds which stabilise the structures of the enzyme

2. enzyme unfolds and precise shape of active site is lost

3. denaturation is irreversible

what happens when enzyme is placed near freezing point

• inactivated

• enzyme activity is very low

• goes back to normal when higher temperatures are restored

how pH affects enzyme activity

1. enzyme at optimum pH (maximum rate of reaction occurs)

2. conformation of active site most ideal for substrate binding

3. highest frequency of effective collisions

4. greatest no. of enzyme-substrate complex formed per unit time

what happens to enzyme activity at pH higher or lower than optimal pH

• H+ concentration changes

• alters bonds that help maintain conformation of enzyme

• active site and substrate binding will be affected

• normally reversible

• denatured at extreme pH changes

how does substrate concentration affect enzyme activity

1. increase in substrate molecules

2. increase in frequency of effective collisions

3. more enzyme substrate complexes formed per unit time

4. rate of reaction increased

why does the increase in substrate concentration produce no change at a certain point

• all active sites of enzymes are currently occupied with substrate molecules

• extra free substrate molecule has to wait for products to be released

how does enzyme concentration affect enzyme activity

1. increase in enzymes

2. increase in frequency of effective collisions

3. more enzyme substrate complexes formed per unit time

4. rate of reaction increased