2. 2 Cell Metabolism Objectives

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2.2 Cell Metabolism


2.2.1 Metabolism

  1. Define the term: metabolism.

2.2.2 Sources of energy

  1. State that solar energy is source of energy on Earth.

  2. State that cellular energy sourced from chemical energy in ATP.

2.2.3 Enzymes

  1. Define the term: enzymes

  2. State the nature, folded shape & functions of enzymes.

  3. Explain the role of enzymes in plants and animals including role in metabolism

  4. Explain the effects of pH & temperature on enzyme activity.

  5. State the procedure and advantages of Bio-processing.

  6. State the use of Bio-processing.

  7. Explain the active site theory to examine enzyme function & specificity.

  8. Explain the term optimum activity with reference to temperature.

  9. Explain the nature of heat denaturation

2.2.7.H Enzymes Extended Study

  1. Explain the active site theory to examine enzyme function & specificity.

  2. Explain the term optimum activity with reference to temperature.

  3. Explain the nature of heat denaturation

Practical activities

ME - Investigate effect of pH on enzyme rate

ME - Investigate effect of temperature on enzyme rate

ME - Prepare one enzyme immobilisation and examine its application

ME - Investigate the effect of heat denaturation on catalase activity

Metabolism is the sum of all the chemical reactions in organisms..

Enzyme reactions can be catabolic (breakdown)

i.e. AB A + B e.g. respiration, digestion

or anabolic (synthetic)

i.e. A + B AB e.g. photosynthesis, protein synthesis.

Catabolic reactions release energy and anabolic reactions require energy normally.

Living organisms obtain their energy either directly from the sun or from food (solar energy or chemical energy. In organisms energy is released from energy stored in bonds of biomolecules during respiration, some used by cells, rest is released as heat.

Enzymes are biological catalysts that control metabolism.

Properties of enzymes

  • Biological catalysts, which can speed up reactions without being used up. They lower the activation energy of the reaction (the amount of energy required to trigger molecules to begin reacting).

  • Proteins, with a particular 3D shape, are produced in living cells.

  • Specific for a particular substrate. One enzyme per reaction.

  • Enzymes can work in both directions (reversible).

  • The activity of the catalyst varies with temperature, pH, enzyme conc., substrate conc., product conc. and enzyme inhibitors.

Enzyme inhibitors

Inhibitors are chemicals that attach to an enzyme and destroy its shape e.g.

  • heavy metals - arsenic, mercury, lead, silver, gold salts.

  • nerve gases e.g. sarin - attack enzymes involved in nerve impulse transmission.

  • cyanide - blocks an enzyme involved in respiration.

  • Antibiotics, drugs, some insecticides – act as inhibitors of enzymes that are not present in humans. They affect other organisms e.g. insects and bacteria.

Naming enzymes - all enzymes are named by adding the suffix -ase to the substrate they act on e.g. lipase acts on lipids.
Amylase (catabolic enzyme) breaks down starch into maltose.

DNA polymerase – an anabolic enzyme that forms and repairs damaged DNA.

Mechanism of enzyme action

  • Substrate combine with active site of enzyme.

  • Induced fit theory – when the substrate joins the enzyme it will change the shape of the active site slightly to make a better fit for the substrate.

  • A temporary enzyme-substrate complex is produced. The bonds in the substrate are altered so that the substrate changes into the product(s).

  • Products leave active site. Active site returns to original shape and can now accept a new substrate.

The mechanism was often referred to as the lock and theory. Substrate = lock and enzyme = key.

Reaction rate is the amount of product formed per unit time or the amount of substrate used up per unit time.

Factors affecting the rate of enzyme action

1. Temperature

The activity of the catalyst varies with temperature. At low temp. the molecules move slowly and collide infrequently, so a low rate of reaction. If too low the enzymes are inactivated. Higher temp. means more frequent collisions so a higher rate. Above optimum temp. shape of active site is altered, so enzyme denatured i.e. their function is permanently destroyed by high temperatures, so rate falls. (humans = 37oC, plants = 20-30oC

2. pH

Most enzymes work within a narrow pH around neutral - can be denatured by a large change in pH i.e. shape of active site altered. Effects of pH are reversible.

Optimum pHs e.g. Pepsin pH 2, most enzymes = 7

3. Substrate concentration

The greater the number of substrate (reactant) molecules, the faster the reaction up to a certain conc. when all active sites have been occupied.
4. Enzyme concentration
In general, the more enzyme the faster the reaction - due to frequent collisions, provided that there is plenty of substrate.

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