3.1.4.2 Many proteins are enzymes

Enzyme

Globular tertiary structure proteins with a specific tertiary structure catalyses reactions

Active site

Small area of enzyme which attaches to substrate to catalyse reaction

Why do active sites have a specific shape?

Specific tertiary structure of protein to bind to complementary substrate

Activation energy

Amount of energy required for reaction to occur

Enzyme effect on activation energy

Enzymes lower activation energy higher rate of reaction

Two models showing enzyme action

Lock and key model

Induced fit model

Explain lock and key model

Enzyme active site is fixed shape and complementary to substrate shape

random collisions mean substrate attaches to enzyme

forming enzyme substrate complex

Charged groups within active site distort substrate

Lowers activation energy

Active site can be reused

Explain induced fit model

Substrate attaches to active site

active site is induced to change shape

Forming enzyme substrate complexes

Change in shape of active site strains bonds located in tertiary structure

Lowers activation energy

Active site returns to original shape after products removed

What factors affect enzymes?

Temperature

pH

Substrate concentration

Enzyme concentration

Inhibitors

Effect of temperature on enzyme as a graph

Explain increase in temperature effect on enzyme activity until optimum temp

temperature increases so enzymes and substrates have more kinetic energy

more successful collisions between substrates and the enzymes' active site per second

more enzymes substrate complexes per second

more product formed per second

Faster rate of reaction

Explain increase in temperature effect on enzyme activity beyond optimum temp

temperature increases beyond optimum temp: HYDROGEN BONDS break between R groups in tertiary structure

Enzyme's ACTIVE SITE DENATURES.

TERTIARY STRUCTURE of the ACTIVE SITE changes so it can no longer become COMPLEMENTARY to the substrate

no ENZYME-SUBSTRATE COMPLEXES can be formed

no PRODUCT is formed

rate of reaction slows down/stops

pH graph for its effect on enzyme activity

Too high/too low pH effect on enzyme activity

Changes charges in amino acids in active site

Breaks ionic bonds in tertiary structure

Active site changes shape

Enzyme denatures

Enzyme-substrate complexes cannot form

pH effect on enzyme activity beyond optimum pH

pH moves away from the optimum, the rate decreases

because the change in pH changes the CHARGES on the R groups of the Amino Acids

changes the IONIC and HYDROGEN bonding between R groups the TERTIARY structure of the enzyme's active site changes enzyme has DENATURED

ACTIVE SITE can no longer become complementary to the substrate

fewer E-S complexes can be formed per second

less product formed per second

Product time Graph for substrate concentration

How to find gradient at a specific time in product-time graph?

Rate of reaction/time graph for substrate concentration

Why is rate of reaction highest when high substrate concentration

Initially lot of SUBSTRATE in excess

more successful COLLISIONS with ACTIVE SITES

more ENZYME-SUBSTRATE COMPLEXES are formed per unit time

more PRODUCT is formed per unit time.

Why does rate of reaction decrease when substrate concentration increases

amount of SUBSTRATE becomes a limiting factor (as some has now formed product)

FEWER successful COLLISIONS with ACTIVE SITES

FEWER ENZYME-SUBSTRATE COMPLEXES are formed per unit time

less PRODUCT is formed per unit time.

slowER rate of reaction

Why does rate of reaction finally reach 0 as substrate concentration increases

ALL of the SUBSTRATE has been converted into PRODUCT

NO MORE successful COLLISIONS with ACTIVE SITES

NO ENZYME-SUBSTRATE COMPLEXES are formed per unit time

no PRODUCT is formed per unit time.

how does substrate concentration affect initial rate of reaction.

Increasing the concentration increases the volume of SUBSTRATE

more successful COLLISIONS with ACTIVE SITES

more ENZYME-SUBSTRATE COMPLEXES are formed

Initially as rate increases, amount of substrate is the limiting factor

However, when the rate is constant, all of the ACTIVE SITES ARE OCCUPIED

concentration of ENZYME/ACTIVE SITES is limiting factor

Enzyme concentration effect on rate of reaction

concentration of enzyme increases, rate of reaction increases

concentration of enzyme is limiting the rate of reaction

more successful collisions between S & active sites

more E-S complexes formed per second

Eventually, substrate conc or temp becomes limiting factor as enzymes conc increases so rate of reaction falls and product formed stays the same

Low enzyme concentration

Enzyme active sites are saturated with substrate

Slower rate of reaction

How do competitive inhibitors work?

Competitive inhibitors similar shape to substrate & complementary shaped to active site

Binds to active site

Compete with substrate but higher substrate concentration outcompetes inhibitor knocking inhibitor out of active site

Rate of reaction Graph for normal substrate conc v.s. Competitive inhibitor

How do non-competitive inhibitors work?

Non-competitive inhibitors bind to allosteric site

Changes tertiary structure of enzyme

Changes tertisry structure and 3D shape of active site

Active site can no longer become complementary to substrate

no enzyme substrate complex can form

Rate of reaction Graph for normal substrate conc v.s. non-competitive inhibitor

Immobilised enzyme definition

Enzymes which can no longer move

By attaching enzyme to a solid support so it can no longer mix freely w/ substrate and product

How to immobilise enzyme

In beads

On things like test strips (like ones used to test for glucose)

3 Advantages of using immobilised enzymes

Continuous process

Bonds can be reused

No need to separate enzymes from products at end

Why is it important to control enzymes?

Prevents all enzymes being active at same time BECAUSE substrates must be digested in correct order

How to control enzymes

Activate/ deactivate enzymes by changing pH (i.e; inhibitors)