Metabolism and Enzymes

Question 1

Metabolism

Answer 1

• Metabolism is made up of two different types of chemical reaction:
  1. Catabolic metabolism is the reactions in which large molecules are broken down to smaller ones. Catabolic reactions release energy. E.g. digestion
  2. Anabolic metabolism is the reactions in which small molecules are built up into larger ones. Anabolic reactions require energy. E.g. protein synthesis.

Question 2

Nutrients

Answer 2

Nutrients are used for growth, repair or maintaining the body, that is, any substance required for metabolism. There are six groups of nutrients:

1. Water
2. Carbohydrates
3. Lipids
4. Proteins
5. Minerals
6. Vitamins

Question 3

Organic Compounds

Answer 3

• Organic compounds are molecules with a carbon chain.

- This includes carbohydrates, lipids, proteins and nucleic acids

Question 4

Carbohydrates

Answer 4

Main source of energy for cells:  
Simple sugars (glucose) are used in cellular respiration to release energy, while complex carbohydrates (starch) are broken down into simple sugars.

Question 5

Lipids

Answer 5

• Includes fats and oil and are another important energy source.
• They are broken down into fatty acids and glycerol. The glycerol can then enter the glycolysis pathway to cellular respiration.
• Other examples of lipids are phospholipids, which are important in the cell membrane, and steroids, including cholesterol and sex hormones.

Question 6

Proteins

Answer 6

• Proteins are made up of many amino acids.
• With regard to metabolism, the most important proteins made are enzymes. Enzymes influence metabolism by controlling the chemical reactions that occur in the body. Proteins can also be used as a source of energy, but only if the supply of carbohydrates and lipids is inadequate.

Question 7

Inorganic Compounds

Answer 7

• Not based on a carbon chain, most don’t contain carbon at all
• Water is important because it dissolves substances and is involved in some chemical reactions
• Minerals may be part of enzymes or substances involved in metabolism
• Vitamins act as coenzymes for many of the chemical reactions of metabolism

Question 8

Chemical Reaction

Answer 8

• There are certain conditions that must be met for a chemical reaction to occur. The reacting particles need to collide with enough energy to break the bonds. This is the activation energy
• The particles must also collide with the correct atoms.
• Chemicals called catalysts are able to decrease the amount of energy needed to break the bonds. This means that the activation energy will be lower and more particles with enough energy to react.

Question 9

Catalyst

Answer 9

• Catalysts are particularly effective because they are not consumed during the reaction, and therefore can influence many reacting particles.
• Catalysts are proteins called enzymes. Enzymes allow chemical reactions to occur at a fast enough rate at body temperature fo the body to function.

Question 10

Enzymes

Answer 10

• The shape of the protein means that enzymes are specific for a particular reaction. The molecule on which an enzyme acts is called the substrate.
• Each enzyme will combine with only one particular substrate and is therefore involved in only one specific reaction. This occurs because the enzyme and its substrate have characteristics that are complementary to one another.
• The part of the enzyme molecule that combines with the substrate is called the active site.

Question 11

Enzymes-Substrate Complex

Answer 11

• When the enzyme and substrate are combined, they are called an enzyme-substrate complex. Two models are used to describe how enzymes function:

1. The Lock and Key Model: states that the shape of the enzyme is always complementary to the shape of the substrate.
2. The Induced Fit Model: states when the enzyme and substrate join, they form weak bonds that cause the shape of the enzyme to change, creating complementary shapes.

Question 12

Factors affecting enzyme activity - pH

Answer 12

• Enzymes are very sensitive to the pH of the medium in which a reaction is taking place
• Each enzyme has an optimum pH at which it will work most effectively.

Question 13

Factors affecting enzyme activity - Temperature

Answer 13

• The rate of most chemical reactions increases as temperature increases.
• This only occurs in a limited temperature ranges;
• If the temperature increases too much, the enzyme will denature (lose its shape)
• If the temperature decreases too much, the enzyme will become inactive.

Question 14

Factors affecting enzyme activity - Presence of Inhibitors

Answer 14

• Are substances that slow or even stop the enzyme’s activity
• Inhibitors may be used by cells to control reactions so that products are produced in specific amounts.

Question 15

Factors affecting enzyme activity - Co-enzymes and co-factors

Answer 15

• Co-factors are ions or non-protein molecules that are required to catalyse a reaction
• Co-factors change the shape of the active site so that the enzymes can combine with the substrate
• Co-enzymes are non-protein organic molecules such as vitamins. They do the same job as co-factors

Question 16

Factors affecting enzyme activity

Answer 16

• The higher the concentration of the enzyme, the faster the rate of a chemical reaction.
• Increasing substrate concentration also increases the rate of a chemical reaction
• The products of a chemical reaction must be continually remoeved otherwise the rate of reaction will slow.