All about Enzymes

Enzymes

..Are The FAQ (Frequently Asked Question ) in SPM...for all papers: paper 1, 2 and even 3.

You dont ever think of leaving this subtopic behind...You have to be well versed or should I say, master it well...

Brief Account
1. Biochemical reactions occur in cells are called metabolism
2. Metabolism includes anabolism and catabolism.
3. Anabolism is the metabolic reactions that build complex molecules, example photosynthesis.
4. Catabolism is the metabolic reactions that break down complex molecules, example respiration and digestion
5. Enzymes are biological catalyst which guide almost all cellular reactions.
6. The general characteristics of enzymes: (FACTS)
· Enzymes are protein
· Enzymes speed up biochemical reactions
· Enzymes are needed in small amount.
· Enzymes are highly specific
· Enzymes reactions are reversible.
· Many enzymes require helper molecules such as cofactor to function.
· Enzymes activities can be slowed down or completely stopped by inhibitors.

For each of the above FACTS, you can elaborate with EXPLANATION…..in your ESSAY

7. Take note of the differences between the intracellular enzyme and extracellular enzyme
8. Ribosomes are the sites of protein synthesis, hence it is the site of enzymes synthesis.
9. The production of extracellular enzymes can be represented using this Diagram:

Sequence of event:

a. Protein that are synthesize in the ribosomes are transported through RER.
b. Protein depart from RER, wrapped in vesicle
c. Transport vesicle fuse with the membrane of Golgi apparatus .
d. Golgi apparatus modified the protein to form enzyme
e. Vesicle bind off from golgi apparatus membrane and travel to plasma membrane
f. Vesicle will fuse with plasma membrane before releasing the enzyme.


10. Factors affecting the rate of enzyme activities:
a. pH
b. temperature
c. substrate concentration
d. enzyme concentration

11.When explaining about the effects of temperature on the activity of enzymes, do not forget to include sentences :
· At low temperature, an enzyme-catalysed reaction takes place slowly because the substrate molecules are moving at a relatively slow rate.
· As the temperature increases, the substrate molecules move faster.
· Collisions between the substrate and enzyme molecules occur more frequently.
· This increase the chances of the substrate molecules coming into contact with the active sites of the enzyme.
· Thus at higher temperature, the rate of reaction between substrate and enzyme increases.
· For every 10 C rise in temperature, the rate of enzyme reaction is doubled.
· This is only true until the optimum temperature is reached.
· The optimum temperature is the temperature at which an enzyme catalyse a reaction at its maximum rate. (37 C)
· Beyond the optimum temperature, any increase in temperature causes the rate of reaction to decrease sharply until it completely stops at 60 C.
· At a very high temperature, the chemical bonds holding the enzymes in their precise shape begin to break.
· This alter the 3-dimensional shape of the enzyme molecules and eventually destroy their active sites.
· So substrate can no longer fit into the active site of the enzyme.
· The enzyme is said to be denatured. (above 40 C)

12.As for the effect of pH:
· A change in pH value can alter the charges on the active sites of an enzyme and the surface of the substrate.
· This can reduce the ability of both molecules to bind with each other.
· In extreme pH condition , the configuration of the enzyme is altered, enzyme structure is altered, destroying its normal function.

13. The effects of substrate concentration on enzyme activity:
· The rate of enzyme-catalysed reaction increases in direct proportion to the substrate concentration until the reaction reaches maximum rate.
· Beyond the maximum rate, the active sites of the enzymes molecules are fully occupied by the substrate molecules,
· So increasing the substrate concentration further has no effect on the rate of reaction.

14. The effects of enzyme concentration on enzyme activity..Explain!

15.As for Paper 3, the possibilities of designing an experiment are as follows:

a. To study the effects of temperature on the activity of salivary amylase

-Manipulated Variable: Temperature of the medium : 0 C, 28 C, 37 C, 45 C, 60 C
-Responding Variable: Time taken for hydrolysis of starch to be completed // Rate of enzymatic reaction.
-Fixed Variable: Volume of saliva (enzyme)

b. To study the effects of pH on the activity of pepsin

-Manipulated Variable: pHof the medium : 3 ,7,8
-Responding Variable: The condition of the mixture after 20 minutes // Rate of enzymatic reaction.
-Fixed Variable: Volume of albumen suspension.

c. To study the effects of substrate concentration on the activity of salivary amylase

-Manipulated Variable: Concentration of starch suspension: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6% -Responding Variable: Time taken for hydrolysis of starch to be completed // Rate of enzymatic reaction.
-Fixed Variable: Concentration of saliva (enzyme)

d. To study the effects of enzyme concentration on the activity of salivary amylase

-Manipulated Variable: Concentration of amylase: 0.2%, 0.4%, 0.6%, 0.8%
-Responding Variable: Time taken for hydrolysis of starch to be completed // Rate of enzymatic reaction.
-Fixed Variable: Substrate concentration

Sample Questions:

1.Figure shows the reaction of an enzyme based on ‘lock and key’ hyphothesis

Based on the figure above, determine the properties of enzyme .

I Enzyme is specific
II Remain unchanged at the end of the reaction
III Enzyme catalysed reactions are reversible
IV Speed up the rates of chemical reaction

A I and II
B I, II and III
C II and IV
D II, III and IV

2. The figure shows the organelles involved in the production of extracellular enzymes.

(a)(i) Using a named example, explain the term extracellular enzyme.
[2 marks]
(ii) Based on the organelles shown, explain how extracellular enzymes are produced.
[8 marks]

(b)The figure shows a reaction of an enzyme and its substrate

Explain the mechanism of the enzymatic reaction [10 marks]

Sample Answer:

1 ( a) (i) - Extracellular enzyme is produced in a cell, then packed and secreted from the cell.
It catalyses its reaction outside the cell. An example is amylase.

- (ii) The instruction for making the extracellular enzyme is transcribed from the deoxyribonucleic acid (DNA) to ribonucleic acid (RNA) in the nucleus.
o The RNA then leaves the nucleus through the nuclear pore
o and attaches itself to the ribosome located on the endoplasmic reticulum.
o When the synthesis of the enzymes is completed
o it is encapsulated in a transport vesicle which fuses with the Golgi body.
o In the Golgi body, the enzyme is further modified before being packed in a secretory vesicle.
o The secretory vesicle transports the enzyme to the plasma membrane, where it fuses with it
o and the enzyme is released outside the cell.

(b) The explanation of enzyme action is known as the ‘lock and key hypothesis’.
· The substrate molecule fits into the active site of the enzyme molecule.
· The substrate is the ‘key’ that fits into the enzyme ‘lock’.
· Various types of bonds such as hydrogen and ionic bonds hold the substrate
· in the active site forming the enzyme-substrate complex.
· Once the complex is formed, the enzyme changes the substrate to its product.
· The product leaves the active site.
· The enzyme is not altered by the reaction and it can be reused.


Sample Question:

1. Discuss the uses of enzymes in the household & industries. Why are enzyme used in these industries.

Suggested Answer :

Enzymes are used as biological detergents.
· Protease degrades coagulated proteins into soluble short-chain peptides.
· Lipase degrades fat or oil stains into soluble fatty acid and glycerol.
· Amylase degrades starch into soluble shorter-chain polysaccharides and sugars.

Enzymes are used in the baking industry.
· Protease is used in the breakdown of proteins in flour for the production of biscuits.
· Amylase is used in the breakdown of some starch to glucose in flour for making white bread, buns and rolls.

Enzymes are used in the medical field.
· Trypsin is used to remove blood clots and to clean wounds.
· Various other enzymes are used in biosensors.

Enzymes are used in industries because:
· They are effective.
· They are cheap and easy to use.
· They can be re-used, thus only small amounts are needed.
· They don't require high temperature to work, thus this reduces fuel costs.

PAPER 3 QUESTION 2- This Qs came out for Paper 3 SPM 2009

A group of students did a study on the function of enzymes as an organic catalyst that can regulate and increase the rate biochemical reactions in the cell. Enzymes are very sensitive to a change in temperature and functions efficiently at an optimum temperature. Design an experiment to study the effect of different temperatures on the activity of salivary amylase on starch.
The planning of your experiment must include the following aspects:

· Statement of identified problem
· Objective of study
· Variables
· Statement of variables
· List of materials and apparatus
· Technique used
· Experimental procedure
· Presentation of data
· Conclusion

Sample answer:

Problem Statement
How does different temperatures Affect the activity of salivary amylase?
Aim: To study the effect of different temperatures on the activity of salivary amylase .

Variables:
Manipulated variables: Temperature.
Responding variables: Time taken for hydrolysis of starch to be completed// Rate of reaction.
Controlled variable: enzyme concentration

Hypothesis:
The rate of reaction of salivary amylase on starch increases with an increase in temperature until it reaches the optimum temperature.

Apparatus & Materials:
Test tube, a dropper, a stopwatch, beakers, a thermometer, a white tile, a Bunsen burner, a tripod stand, test-tube rack, a wire gauze.
1 % starch solution, salivary amylase solution, ice cubes, distilled water, iodine test solution.
Technique
Measure and record the time taken for hydrolysis of starch to be completed using stopwatch
Procedure:
1. Collect 5 ml of saliva and dilute it with 5 ml of distilled water and labelled test tube X.
2. Put 1 ml saliva in each test tube labelled A, B, C, D and E.
3. Pour 5 ml of 1 % starch solution into each test tube labelled A, B, C, D and E.
4. Immerse test tube A and X, in water bath where the temperature is fixed at 5C and leave it for 10 minutes.
5. Prepare a piece of white tile and drop iodine solution on it.
6. After 5 minutes pour 2ml of saliva from test tube X to the starch solution in test tube A. Start the stop watch.
7. Repeat the iodine test for the mixture from test tube A at intervals of 1 minute.
8. Record the time taken for the mixture from A to change in colour of iodine solution until it does not change.
9. Repeat steps 4 to 8 for test tubes B, C, D and E with water temperatures fixed at 28C, 37C, 45C and 60C respectively.
10. The results are recorded in a table.

Result:

Conclusion:
The rate of increase of enzyme action increases with an increase in temperature until it reaches the optimum temperature. Hypothesis accepted

...Happy Revising..