4: Enzymes and Metabolism

Question 1

What is metabolism?

Answer 1

Metabolism is the sum of the chemical reactions that take place in an organism. It includes two types of metabolic reactions, namely catabolism and anabolism.

Question 2

What is catabolism?

Answer 2

Catabolism refers to the breaking-down reactions in an organism. In catabolic reactions, complex molecules are broken down into simpler molecules with the release of energy.
An example of catabolism is the breakdown of glucose molecules into carbon dioxide and water during respiration. Energy is released in the process.

Question 3

What is anabolism?

Answer 3

Anabolism refers to the building-up reactions in an organism. In anabolic reactions, complex molecules are synthesised from simpler molecules. Energy is required to drive the reactions.
An example of anabolism is the synthesis of glucose molecules from carbon dioxide and water during photosynthesis, Sunlight provides energy for the process.

Question 4

What is the role of enzymes in metabolism?

Answer 4

For every reaction, a certain amount of energy must be supplied to the reactants before the reaction can occur. This energy is called the activation energy. It is like how energy is needed to push a rock up to a hilltop before it can roll down.
In our body, enzymes are present and function as biological catalysts. They help lower the activation energy so that chemical reactions can take place at body temperature at a faster rate.

Question 5

What are exergonic and endergonic reactions?

Answer 5

Exergonic reactions release energy, making the energy level of products lower than that of reactants. Catabolic reactions are exergonic.
Endergonic reactions absorb energy, making the energy level of products higher than that of reactants. Anabolic reactions are endergonic.

Question 6

How do enzymes work?

Answer 6

Enzymes are special types of proteins produced in organisms. On each enzyme molecule, there is an active site. The active site has a specific shape. An enzyme molecule only binds to substrate molecules that fit the shape of its active site.

Question 7

How do metabolic reactions take place?

Answer 7

A metabolic reaction begins when the substrate molecule(s) bind to the active site of an enzyme molecule to form an enzyme-substrate complex. The formation of the enzyme-substrate complex greatly lowers the activation energy of the reaction. The substrate(s) are converted into product(s), which dissociate from the enzyme molecule. The enzyme molecule is released in its original form and can be reused.
In catabolic reactions, the active site binds to a substrate molecule and helps split it apart. In anabolic reactions, the active site binds two or more substrate molecules and helps join them together.

Question 8

How can the specificity of enzyme actions be explained with an analogy?

Answer 8

It can be explained with the lock-and-key hypothesis: A key of a specific shape fits only one lock. Similarly, an enzyme with an active site of a specific shape binds only to a particular type of substrate.

Question 9

What are the properties of enzymes?

Answer 9

1. Enzymes are biological catalysts: They speed up metabolical reactions in organisms by lowering the activation energy of reactions.
2. The action of enzymes are specific: An enzyme only acts on substrates that fit into its active site. Each type of enzyme has its unique active site. Therefore, one type of enzyme can only catalyse one type of reaction. Hence, enzymes are said to be specific in action.
3. Enzymes are proteins: Their structures and activity sir easily affected by temperature and pH. Most of them are denatured at high temperatures and extreme values of pH.
4. Enzymes are reusable: They remain unchanged after reactions, enabling them to bind again to other substrate molecules after a reaction is complete.
5. Enzymes are needed in relatively small amounts since they are reusable.

Question 10

How does temperature affect the rate of an enzymatic reaction?

Answer 10

At low temperatures, the enzymes are inactive. the kinetic energy of enzyme and substrate molecules is low. The molecules move slowly and the chance for them to collide with each other is low. Therefore, the chance of forming enzyme-substrate complexes is low. The reaction rate is low.
As the temperature rises, most enzyme and substrate molecules have more kinetic energy. They move around more rapidly and collide with each other more frequently. This increases the chance of forming enzyme-substrate complexes. As a result, the rate of the enzymatic reaction increases.
As the temperature continues to rise, the rate of enzymatic reaction will eventually reach a maximum at the optimum temperature.
High temperatures may cause conformational damage (a change in shape) in the active site of the enzyme molecule. The enzyme is said to be denatured. The substrate molecule can no longer fit into the active site of the enzyme to form an enzyme-substrate complex. The rate o enzymatic reaction decreases.

Question 11

How does pH affect the rate of an enzymatic reaction?

Answer 11

Most enzymes work in a narrow range of pH. They work best at their optimum pH.
An unsuitable pH may cause conformational damage in the active site of the enzyme molecule (the denaturation of the enzyme). The substrate molecule can no longer fit into the active site of the enzyme to form an enzyme-substrate complex. The rate of enzymatic reaction decreases.

Question 12

What are inhibitors?

Answer 12

Inhibitors are chemicals that can decrease the rate of enzyme reactions. Examples of inhibitor include cyanide and heavy metals like mercury ions, lead(II) ions, and copper(II) ions.

Question 13

How are enzymes applied in biological washing powders?

Answer 13

They contain proteases and lipases. These enzymes help break down insoluble proteins and lipids in stains into soluble products (amino acids, glycerol, fatty acids), which can be removed by water easily.

Question 14

How are enzymes applied in manufacturing stonewashed jeans?

Answer 14

In the past, stone washed jeans were produced by washing the jeans with stones. Now, cellulase is used in the production instead. It helps break down the cellulose fibres of the jeans to produce a similar effect to stonewashing.

Question 15

How are enzymes applied in contact lens cleaners?

Answer 15

Some contact lens cleaners contain proteases, which can help remove the proteins deposited on the contact lens.

Question 16

How are enzymes applied in meat tenderisers?

Answer 16

Meat tenderisers contain papain, a protease extracted from papaya. Papain helps break down protein fibres in meat so that the meat becomes soft.

Question 17

How are enzymes applied in the production of cheese?

Answer 17

Proteases extracted from young cows’ stomach are used for coagulating milk to produce cheese.

Question 18

How are enzymes applied in the production of fruit juices?

Answer 18

Pectin is a substance in plant cell walls. The presence of pectic in fruit juices ,ales the juices look cloudy. Pectinase is used to break down the pectin in the juices, so that the juices look clear.

Question 19

What are the advantages of using enzymes in the production of commercial products?

Answer 19

1. Enzymes can speed up chemical reactions. This shortens the production time and allows mass production of products.
2. Enzymes are specific in action. This can reduce the production of unwanted products.
3. Enzymes are reusable and are needed in small amounts only. This lowers the cost of production.
4. Many enzymes work at moderate conditions. Using enzymes in the production processes does not require extreme conditions, such as very high temperatures and pressures.

Question 20

What are the limitations of using enzymes in the production of commercial products?

Answer 20

1. Enzymes are sensitive to temperature and pH change. High temperatures and unsuitable pH can cause denaturation of enzymes.
2. Enzymes are easily affected by inhibitors. All containers that are used in the production processes have to be clean to prevent them from contamination with inhibitors.