chap. 5 enzymes biology o levels

7/28/2019 Chap. 5 Enzymes Biology O levels

1/28

Chapter 5

Enzymes


2/28

Learning Outcomes

1. Define enzymes as proteins which

function as biological catalysts.

2. Explain enzyme action in terms of the

lock and key hypothesis

3. Investigate and describe the effect of

temperature and of pH on enzyme

activity


3/28

What is a catalyst?

1. A substance that speeds up the rate of a

chemical reaction.

2. Enzymes are biological catalysts.


4/28

What is an enzyme?

Enzymes are special compounds

produced by living cells in a body of anorganism that allow chemical reactions to

take place at a faster rate.

They act as catalysts.

They are made of protein.

They alter the rate of chemical reactionswithout themselves being chemically

changed.

Each enzyme has a unique shape.


5/28

Importance

Vital to maintain normal functioning in an

organism


6/28

Uses

1. Digestion

Complex insoluble molecules are broken

down into small soluble molecules

2. Cellular respiration

Oxidation of glucose to produce energy

3. Germination of seeds


7/28

Types of enzymes

1. Extracellular enzymes

Enzymes leave the cell in which they

were produced to exert their functions

outside the cell.

Eg salivary amylase


8/28

2. Intracellular enzymes

Enzymes exert their action inside the cells

Egs:- lysozyme in lysosomes


9/28

Enzyme action

1. Lock and key hypothesis

2. Enzyme catalyzed reaction:-

Lock = enzyme moleculeKey = substrate molecule
http://localhost/var/www/apps/conversion/tmp/enzyme.movhttp://localhost/var/www/apps/conversion/tmp/enzyme.mov


10/28

enzyme

Active

site

substrate

Enzyme

substrate

complex

enzymeproducts


11/28

amylase

Active

site

starch

Enzyme

substrate

complex

amylase2 maltose

units


12/28

Classification of enzymes

1. Hydrolysis = splitting of water (watermolecules are needed to break downcomplex molecules)

2. Called hydrolases.Eg. (a) carbohydrases (carbohydrates)

(b) amylases (starch)

(c) cellulases (cellulose)(d) proteases (proteins)

(e) lipases (fats)


13/28

Characteristics of Enzymes

1. Enzymes and speed of chemical

reactions

Enzymes alter or speed up the rates of

chemical reactions that occur in a cell.

Enzymes remain unchanged in the

reactions

Enzymes can be reused over and over

again


14/28

2. Enzymes are required in minute

amounts

A very small amount of enzyme is capable

of catalyzing a huge reaction.


15/28

3. Enzymes are VERY specific.

Amylases will only act on starch and NOT

on proteins or fats.

The substances that enzymes act on are

called substrates ( starch, proteins and

fats)


16/28

4. Enzyme activity is affected by temperature.

Enzymes have an optimum temperature at

which they function very effectively.

At low temperatures, enzymes are inactive.

As the temperature increases, the rate of

reaction increases.

Beyond the optimum temperature, the enzymeactivity decreases as the enzyme is denatured.


17/28

Temperature

Rate of

reaction

Optimum

temperature

Enzyme is denatured.

Structure is changed


18/28

5. Enzyme activity is affected by pH

Enzymes are affected by the acidity oralkalinity of solutions.

Some work best in acidic environment (egpepsin)

Alkaline environment ( intestinal enzymes

eg amylase)Extreme changes in pH can denature the

enzymes.


19/28

pH

Rate of

reaction

7

Optimum pH


20/28

Why do enzymes denature?

1. Enzymes are made of proteins

2. Proteins heat them up changes

their shape

3. Their 3-D structure is changed.

4. Changes are made to the active site.


21/28

If you increase the concentration of

substrate, the speed of enzyme

reaction will increase. But, there willcome a time when any more increase

in the substrate concentration will not

increase the speed of reaction.WHY?


22/28

What happens at low substrate

concentration?

At low substrate concentrations,

collisions between enzyme and

substrate molecules are infrequent and

reaction proceeds slowly.


23/28

As the substrate concentration

increases, the rate of reaction initially

increases proportionately as collisions

between enzyme molecules andsubstrates become more frequent.


24/28


25/28


26/28

Enzyme Concentration


27/28

Learning Outcomes

1. Define enzymes as proteins which

function as biological catalysts.

2. Explain enzyme action in terms of the

lock and key hypothesis

3. Investigate and describe the effect of

temperature and of pH on enzyme

activity


28/28

Design a mind map tosummerise the properties

and nature of enzymes

chap. 5 enzymes biology o levels

Documents