Enzymes : Biology WJEC AS

Structure

Globular proteins - tertiary structure

Structure: Bonds

Hydrogen Bonds
Ionic Bonds
Disulphide Bonds

Function

•Biological catalysts- speed up rate of reaction
-Reusable (unchanged)
-Specific

PRACTICAL- Enzyme Activity

H2O2 (hydrogen peroxide) --> H20 + O2

-Soak paper disc in enzyme (catalase)
-O2 collects on disc
-Disc rises to surface

Lock and Key Model

Substrate is complementary to active site.

Induced Fit Model

-Substrate doesn't quite fit active site.
-Enzyme slightly alters shape of active site as the substrate binds.
[example: LYSOZYME- an enzyme in tears and saliva- needs to alter as there are many different bacteria]

Activation Energy

Enzymes lower AE- less energy needed to react.

~ This happens as the active sites puts strain on the substrate. This weakens their bonds, so they break easier.

Turnover Number

The max. molecules of substrate that can be converted to product (over unit of time)

Factors Affecting Enzyme Activity

1) pH
2) Temperature
3) Substrate Conc.
4) Enzyme Conc.
5) Presence of Inhibitors

Anabolic Reactions

Small + Small = Large Molecule

(condensation reactions- producing larger molecules)

Catabolic Reactions

Breaking down larger molecules = smaller ones.

Intracellular Enzymes

Inside the cell.
(respiratory enzymes- break down glucose to make ATP)

Extracellular Enzymes

Released to work outside the cell.
(digestive enzymes- released onto food to break it down)

Ways to Measure Enzyme Activity

1) Time taken for reaction.
2) Rate of reaction (1/time).
3) Concentration (amount) of products formed.

PLOTTING GRAPH

x axis- whatever you CHANGED

y axis- whatever you MEASURED

Effect of Temperature

•Little KE, so move slowly ~ Few successful collisions ~ Few E-S complexes ~ Little product

((INCREASES))

•OPTIMUM- max rate of reaction/least time taken•

•Eventually DENATURE ~ vibration causes bonds to break ~ tertiary structure breaks ~ changes shape!

Effect of pH

The H+ or OH- ions interfere with hydrogen & ionic bonds.

(H+) ~ Ions fill the active site- they're attracted to negative R groups. IONIC BONDS BREAK!!
Also repel substrate...

Effect of Changing Substrate Conc.

•Low Substrate Conc: limiting factor- not all active sites able to be filled :(
((OPTIMUM- max E-S complexes form))
•High Substrate Conc: PLATEAUS as enzyme conc is limiting factor- all active sites occupied.
Rate of reaction now depends on enzyme turnover number!!

Effect of Changing Enzyme Conc.

Linear relationship if substate is also added in excess**

•Low conc- not enough active sites= few E-SCs=long time taken. (enzyme conc is limiting factor)

((INCREASES AS MORE ACTIVE SITES ADDED))

•EVENTUALLY PLATEAUS~ substrate conc is limiting factor- not enough substrates to fill the active sites.

Source of Industrial Enzymes

Obtained from micro organisms such as fungi and bacteria.
•Grown in fermenters
•Reproduce rapidly
•Produce enzymes as part of usual metabolic activity.

•MOs killed- enzymes are isolated/extracted.

Protease Enzyme

(made by a bacteria)
•breaks protein stains~ biological washing powders.
•tenders meat (breaks down proteins)

Immobilised Enzymes

When an enzyme is fixed to an inert, insoluble matrix [lacks the ability to move]

Four Methods of Immobilisation

•Adsorption
•Entrapment
•Encapsulation
•Chemical Bonding

Method : Adsorption

(onto glass/clay/collagen)
Binded/attached BUT not taken across the membrane.

Method : Entrapment

Entrapped in a cellulose mesh.

Method : Encapsulation

Encapsulated in alginate beads.

Method : Chemical Bonding

Enzymes are covalently bonded to each other. (STRONG)

Activation Energy

LOWERED BY ENZYMES
-Energy needed to break existing chemical bonds inside molecules in order to start a chemical reaction.

Metabolism

All chemical processes of an organism.
ANABOLIC- small--> larger
CATABOLIC- large--> smaller

Initial Reaction Rate

Measured in first 30 secs. Doubled to get rate per minute.

~ highest rate of reaction due to high number of substrates colliding with enzymes.

Control

An experiment isolating effect of one variable (IV).
All variable kept constant except one.
For example, enzyme denatured to prove it's responsible for the reaction.