Enzymes

why are enzymes required

Many metabolic reactions require high temperatures and pressures to occur

Not possible in body as would damage cells

what is the role of enzymes

speed up rate of metabolic reactions by lowering the activation energy

what is an anabolic reaction

Endothermic

Building up larger molecules from smaller ones

E.g cellulose

what is a catabolic reaction

Exothermic

Breaking down larger molecules to release energy

E.g. glucose

Mechanism of enzyme action (8 steps)

Molecules in a solution move and collide randomly

Enzyme and substrate collide in the correct orientation- successful collision

Enzyme - substrate complex is formed

Bonds in substrate are weakened

Activatio energy is reduced

Reaction occurs and product forms - enzyme product complex

Product then released

Enzyme catalyses another substrate

what is the Lock and Key hypothesis (4)

Active site is highly specific

Only the correct substrate fits in it

R - groups within active site interact with substrate

Weakening bonds within substrate

Induced Fit hypothesis (4)

Active site changes shape slightly when substrate binds

Interactions between active site and substrate induces changes in enzyme’s tertiary structure

This strengthens the bonding with substrate

Weaking bonds in the substrate

function of catalse

Hydrogen peroxide is a toxic product of many metabolic reactions

Catalase quickly breaks it down into hydrogen and oxygen

function of extracellular enzymes

Secreted by cells to break down larger nutrients to be absorbed by the cell

function of amylase

Partially breaks down starch polymers

Into disaccharide maltose

Produced by salivary glands and pancreas

where is amylase produced

in salivary glands and pancreas

function of maltase and where is it present

Present in small intestine

Breaks down maltose into glucose

function of tripsin and where is it present

A protease enzyme

Digestion of proteins into smaller peptides

Produced in pancreas and released into small initestine

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Effect of temperature on enzyme catalysed reactions (7)

Initially rate of reaction increases with temperature

Enzyme and substrate have more kinetic energy so more frequent collisions

Vmax at optimum temperature

After optimum temperature rate of reaction drops rapidly

Bonds in tertiary structure vibrate and break

Active site changes shape and substrate can no longer bind

Enzyme denatures

what is the tmperature coefficient

Q10

Measure of how much rate of reaction increases with 10 degree rise in temp

Usually 2

Effect of pH on enzyme catalysed reactions

Hydrogen and ionic bonds in tertiary structure contribute to unique shape of active site

pH is measure of H+ ion concentration

Active site is only right shape at certain H+ concentration (optimum pH)

Enzyme denatures if pH shifts from optimum

But can renature if pH is back to optimum

Produces a bell - curve graph

Effect of increasing substrate concentration on enzyme catalysed reactions (5)

More substrate molecules per unit volume

More frequent successful collisions

Rate of reaction increases

At Vmax all the active sites are occupied

Enzyme concentration is now limiting

Effect on increasing enzyme concentration on enzyme catalysed reactions (5)

More enzyme molecucles per unit volume

More frequent collisions

Rate of reaction increases

At Vmax all the substrates are being catalysed

Substrate concentration is now limiting

how do competitive inhibitors work

Similar shape and size to substrate

Competes with substrate to bind with active site of enzyme

Less substrates catalysed by enzymes

Rate of reaction is reduced

What impact do competitive inhibitors have on the Vmax

Vmax remains the same

As if substrate concentration is increased enough

The rate of reaction can reach the original Vmax

function of statin

Competitively inhibit enzymes involved in cholesterol synthesis

Reversible

function of aspirin

Non competitively inhibits action of COX enzymes

Binds to allesteric site and changes shape of active site

function of non - competitive inhibitor

Inhibitor binds to enzyme on the allesteric site causing tertiary structure of the enzyme to change

Active site changes shape

Substrate can no longer bind

Vmax is decreased

what is end product inhibition

The product of an enzyme catalysed reaction inhibits the enzyme

Ensures excess products are not made - prevents wasting resources

Like a negative feedback cycle

what is a cofactor

molecule which binds to enzyme and allows enzyme substrate complex to form more easily

what is a coenzyme

organic cofactor

usually sourced from vitamins

what is a prosthetic group

cofactor that is permanently bound to an enzyme

Cofactor for amylase

Cl- ion

Prosthetic group for carbonic anhydrase

Zn2+ ion

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what is an inactive precursor enzyme

Inactive form of an enzyme

Which requires a hydrolysis reaction or addition of a cofactor to reveal the active site

Used to control action of certain harmful enzymes

what is a holoenzyme

Complete functional enzyme

Apoenzyme + cofactor = holoenzyme

example of intracellular enzyme

catalase

2 examples of extracellular enzymes

amylase and trypsin