IGCSE BIOLOGY TOPIC 20 BIOTECHNOLOGY

Genetic engineering is the process of artificially altering genes in a cell to change the way it
works. This could be to make the cell perform a desired function, such as making a specific
protein, or to make the cell resistant to different factors. For example, some strawberries have
been genetically modified to become resistant to frost by inserting a gene taken from cold
water fish which makes antifreeze proteins.
Genetic engineering and bacteria:
Bacteria are useful to genetic engineering as they reproduce very rapidly but still have the
ability to produce complex molecules. Bacteria contain plasmids, which are circular rings of
DNA, into which new genes can be inserted, removed or changed. There are also no ethical
concerns about manipulating the DNA of bacteria.
Bacteria can be manipulated to produce human proteins, such as insulin:

  1. The gene which codes for the desired protein is located and isolated using restriction
    enzymes. The isolated gene has “sticky ends”.
  2. The plasmid from the bacterial cell is cut with the same restriction enzymes. This leaves
    complementary sticky ends to the isolated gene.
  3. The gene is inserted into the plasmid. The complementary sticky ends are joined using
    the enzyme DNA ligase. This forms a recombinant plasmid.
  4. This plasmid is inserted into the bacteria, which will then produce this protein as the
    inserted gene is expressed.
  5. The bacterial cell reproduces, making more cells which produce the protein.
    Examples of genetic engineering:
    ● Insulin production – people with diabetes must take insulin to regulate their bloodglucose concentration. Insulin was originally harvested from animals, such as pigs,
    although this had slight differences to human insulin, which made some people allergic
    to it. Genetic engineering has allowed human insulin to be made in bacteria cells. This
    produces cheap, human insulin in high quantities.
    ● Herbicide and insect resistant plants – genes can be inserted into plants to make them
    resistant to herbicides and insects. This means that less crops die, so farmers have a
    larger crop yield.
    ● Vitamin-rich plants – some plants can be genetically modified to increase the number of
    vitamins in them. This is beneficial to places where certain vitamins are hard to find to
    reduce vitamin deficiency. For example, “golden rice” is a type of rice that has been
    genetically modified to produce beta carotene, which humans use to produce vitamin A.
    This reduces vitamin A deficiency in some areas.

Disadvantages of genetic engineering:
● Loss of biodiversity.
● Potential development of weeds that are resistant to herbicides.
● GM crops are more expensive.
● GM crops may contaminate wild species by crossbreeding.
● Long-term health impacts not known.
Biotechnology:
Biotechnology involves using microorganisms and biological substances to carry out functions
in manufacturing processes:
● Yeast is a microorganism which can respire anaerobically (without oxygen) to release
carbon dioxide. This can be used in bread-making to make dough rise as bubbles of
carbon dioxide form. Ethanol is also released during this reaction, which can be used to
make biofuels that are used as an alternative to fossil fuels.
● Pectinase is an enzyme used in fruit juice production. Pectinase breaks down pectin,
which is found in plant cell walls and is used to hold the cell wall together. Adding
pectinase therefore breaks down these walls to release the contents of the cell, which
increases the yield of fruit juice.
● Biological washing powders contain enzymes to break down different molecules.
Amylases break down starch, lipases break down fats and oils, and proteases break
down proteins. Enzymes break these into smaller products that are water soluble, thus
can be washed out easily. As enzymes are denatured at high temperatures and extreme
pH, a lower washing temperature is needed, and the enzymes may not work in acidic or
alkaline water.
● The enzyme lactase can be used to make lactose-free milk. When lactase is added to
milk, it breaks down the lactose into glucose and galactose, which can be safely
consumed by lactose-intolerant people.
● Penicillium is a fungus used to produce penicillin, an antibiotic. The fungus is placed in a
fermenter to keep it at the optimum temperature and pH, so the penicillin yield is high.
There is also an air inlet so that aerobic respiration can take place, and all other
microorganisms are killed to limit contamination and competition.

MAIN NOTES

 Biotechnology and genetic engineering

  • Biotechnology is the application of biological organisms, systems or processes to manufacturing and service industries.
  • Genetic engineering involves the transfer of genes from one organism to (usually) an unrelated species.
  • Both processes often make use of bacteria because of their ability to make complex molecules (eg. proteins) and their rapid reproduction rate.
  • Bacteria are useful in biotechnology and genetic engineering because they can be grown and manipulated without raising ethical concerns.
  • They have a genetic code that is the same as all other organisms, so genes from other animals or plants can be successfully transferred into bacterial DNA.
  • Bacterial DNA is in the form of a circular strand and also small circular pieces called plasmids.
  • Scientists have developed techniques to cut open these plasmids and insert sections of DNA from other organisms into them.
  • When the bacterium divides, the DNA in the modified plasmid is copied, including the ‘foreign’ DNA.

This may contain a gene to make a particular protein such as insulin, which can be extracted and used as a medicine to treat diabetes.

Genetic engineering

Genetic engineering: is changing the genetic material of an organism by removing, changing or inserting individual genes.

Examples of genetic engineering:

  • The insertion of human genes into bacteria to produce human insulin.
  • The insertion of genes into crop plants to confer resistance to herbicides and insect pests.
  • The insertion of genes into crop plants to provide additional vitamins.

Bacterial production of a human protein such as insulin:

  1. Isolation of the DNA making up a human gene using restriction enzymes, forming sticky ends.
  2. Cutting of bacterial plasmid DNA with the same RE, forming complementary sticky ends.
  3. Insertion of human DNA into bacterial plasmid DNA using ligase enzymes to form a recombinant plasmid.
  4. Insertion of plasmid into bacteria.
  5. Replication of bacteria containing recombinant plasmid which make human protein as they express the gene.
  • Restriction enzymes cut DNA at specific sites, rather than just in random places along the DNA molecule. Eg. between the A and the T in the sequence GAA-TTC.
  • ligase enzymes join pieces of DNA together at specific sites.
  • The plasmids are said the be vectors that carry the human DNA into the bacteria and the techniques are sometimes called gene-splicing.
  • The bacteria are cultured in special vessels called fermenters and the insulin that they produce can be extracted from the culture medium and purified for use in treating diabetes.

Golden rice:

Advantages

  • Produces beta carotene which is needed by humans in order to make vitamin A.
  • Used in areas where vitamin A deficiency is common, so it can help prevent night blindness.

Disadvantages

  • beta carotene levels in golden rice may not be high enough to make a difference.
  • there are fears that it will cross-breed with and contaminate wild rice.
  • there are concerns that food from GM plants might harm people.
  • seed for GM plants can be expensive.

Soya and Maize:

Disadvantages

  • Can contain pesticide residues or substances that causes allergies (allergens).

Herbicide-resistant crops:

Disadvantages

  • The potential development of herbicide-resistant weeds.

Loss of biodiversity because fewer weeds survive – resulting in reduced food and shelter for animals.

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