A2/A-level Biology - Biotechnology and Gene Technologies (1)

• The industrial use of living organisms (or parts of living organisms) to produce food, drugs or other products.

When it comes to A2/A-level Biology, do you know why microorganisms are often used in biotechnological processes?

Many biotechnological processes make use of microorganisms (bacteria and fungi) as they have many advantages:

• Rapid growth in favourable conditions.
• Proteins and chemicals produced can be harvested.
• Can be genetically engineered to produce specific products.
• Grows well at low temperatures – lower than those chemical processes.
• Can be grown anywhere – not climate-dependent.
• Purer products than those produced in chemical processes.
• Can be grown using nutrient materials that are useless or toxic to humans.

• A culture is a growth of microorganisms.
• A pure culture contains one microorganism and a mixed culture contains multiple species.

1.    Lag phase

• Organisms are adjusting to surroundings (taking in water, cell expansion, activating specific genes, synthesising specific enzymes.
• Cells are active but not reproductive = population remains fairly constant.

2.    Log (exponential) phase

• Population size doubles each generation as every individual has enough space and nutrients to reproduce.

3.    Stationary phase

• Nutrient levels decrease and waste products and other metabolites build up.
• Rate of death is equal to rate of reproduction.

4.    Decline/death phase

• Nutrient exhaustion and increased levels of waste products and metabolites lead to death rate exceeding reproduction rate.
• Eventually, all organisms will die in a closed system.

• This is where enzymes are held, separated from the reaction mixture.
• Substrate molecules can bind to the enzyme molecules and the products formed go back into the reaction mixture leaving the enzyme molecules in place.
• Methods for immobilising enzymes depend on ease of preparation, cost, relative importance of enzyme ‘leakage’ and efficiency of the particular enzyme that is immobilised.

Adsorption   

• Enzyme molecules are mixed with immobilising support and bind to it due to hydrophobic interactions and ionic links.
• Bonding forces are not particularly strong so enzymes can become detached (leakage), however this method can give very high reaction rates.
• Adsorption agents: porous carbon, glass beads, clays and resins.

Covalent Bonding   

• Enzymes are covalently bonded to a support, often an insoluble material such as clay particles using a cross-linking agent such as gluteraldehyde and sepharose.
• This method does not immobilise a large quantity of enzyme but binding is very strong so there is very little leakage of enzyme from the support.

Entrapment   

• Enzymes are trapped, e.g. in a glass bead or a network or cellulose fibres.
• Reaction rates can be reduced as substrate molecules need to get through the trapping barrier.
• The active site is less easily available than other methods.

Membrane separation   

• Enzymes are separated from the substrate mixture by a partially permeable membrane.
• The enzyme solution is held at one side of a membrane whilst substrate solution is passed along the other side.
• Substrate molecules are small enough to pass through the membrane to the enzyme.
• Product molecules are small enough to pass back through the membrane.

• In many areas of clinical research and diagnosis and in some industrial processes, the product of a single chemical reaction is required.
• It is often more efficient to use isolated enzymes to carry out the reaction rather than growing the whole organism or using an inorganic catalyst.
• Isolated enzymes can be produced in large quantities in commercial biotechnological processes.

• The extraction of enzyme from the fermentation mixture, involving separation and purification of any product of large-scale fermentations.

Industrial-scale fermentations can be operated in two ways:
(1) Batch culture:

• The microorganism is mixed with a specific quantity of nutrient solution.
• It is left to grow for a fixed period with no further nutrient added.
• At the end of the period, the products are removed and the fermentation tank is emptied.
• E.g., pencillin.

(2) Continuous culture:

• Nutrients are added to the fermentation tank.
• Products are removed from the fermentation tank at regular intervals/continuously.
• E.g., insulin.

In part 2, you will know more about metabolites.

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Drafted by Bonnie (Biology)