Genetic Engineering - Sicm


Dec 11, 2012 (5 years and 6 months ago)


Genetic Engineering

- this is one of the most significant scientific advances of modern times
- it is the technology that allows genes to be altered and transferred from one
organism to another
- therefore, useful genes can be taken from a donor organism and given to a host
organism where the gene will continue to produce its product.
- a gene carried the genetic code for the production of an enzyme (an enzyme is a
- for example, the human gene for insulin can be extracted as mRNA. This can then
be used to produce insulin to treat diabetes.

This process has a number of steps:
1. The required gene is identified
2. The gene must be isolated (cut-out)
3. The gene is inserted into a vector (this is a bacterial plasmid – a circular strand of
DNA in a bacterial cell)
4. The plasmid is placed into the bacterium or host cell
5. The bacterium is allowed to produce numerous identical cells
6. The host cell produced the product (e.g. insulin)
7. The insulin is separated and purified

Further information about procedure:

(a) the required gene is cut out of the DNA strand by an endonuclease (enzyme)
- this enzyme cuts the DNA at specific points
- it leaves “sticky-ends” – which allow other genes to rejoin
(b) the same restriction enzyme (endonuclease) is used to cut the bacterial
plasmid (leaving the same sticky ends)
(c) the required gene is inserted into the plasmid ring using a ligase enzyme. The
plasmid ring acts as a vector – transferring the gene.
(d) the plasmid is then put back into the bacterium, which is allowed to reproduce
by mitosis (i.e. produce clones)
(e) the product is then purified and used

Human Insulin – as an example
- extract from the host cell the mRNA (messenger RNA) that codes for the
production of insulin
- add reverse transcriptase which produces the DNA code from the mRNA
- cut the plasmid using the endonuclease
- insert the DNA code for insulin with ligase
- return the plasmid to the bacterium and allow to reproduce
Protein Synthesis

How it happens

1. DNA unzips in particular region
2. mRNA is manufactured from 1 strand of DNA
- mRNA is one strand of DNA which is created by nucleotides binding to one
strand of the real DNA. RNA is always one strand. Another difference is that
it is normally shorter and there is no Thymine. This is substituted for Uracil.
3. mRNA leaves the nucleus via nuclear pores and goes towards ribosomes
4. Ribosomes read code on mRNA
5. They direct tRNA (another form of RNA – basically just three nucleotides that join
to the mRNA) to form appropriate amino acids.
6. Amino acids are joined together by peptide bonds to form proteins.

Uses of genetic engineering

(a) genetically engineered bacteria which break down oils into soluble sugars
(b) genes which give resistance to plants from various diseases
(c) genes inserted to the roots of non-leguminous plants to allow them to fix
atmospheric nitrogen – reducing the need for fertilisers and so reducing pollution
(d) genes inserted into cows / sheep for human milk production (lower in fat)
(e) genetically engineered sheep that produce Factor VIII – needed by haemophiliacs
(f) genes inserted into plants to slow food deterioration
(g) bacteria have genes inserted in them to produce a particular product

DNA (unwound)
amino acid
Advantages of genetic engineering
- fast
- cost effective
- reliable
- saves lives
- enabled rapid research
- increases resistance to disease by crops
- increases crop yield
- reduces crop production cost
- less fertiliser / pesticide needed

Disadvantages of genetic engineering
- can the gene “jump” from one species to another? o e.g. weed-killer resistance can jump to weeds themselves
- taste affected o e.g. tomatoes that produce pesticide
- could the product damage / harm the consumer o e.g. contain harmful chemical applied to it
- increase resistance in the attacking organism
- moral / ethical problems o re-manipulation of life?

- the production of genetically identical offspring (i.e. exactly the same DNA)
- used in bio culture and animal husbandry (farming)


(a) Cuttings from stems / leaves / roots enable large numbers of genetically identical
plants to be produced from the parent:
i. simple form of cloning
ii. already used for hundreds of years

(b) Tissue culture
Method of producing genetically identical plants from one species of plant tissue
- small piece of tissue is taken (size of rice grain)
- placed on sterile agar jelly
- agar contains nutrients needed
- a suitable temperature is provided (≈ 25ºC)
- hormones to stimulate cell division (by mitosis) is added
- cells divide to form completely new plants
- add water


- many plants produced
- short time (i.e. fast)
- endangered species are increased in number
- little space is required
- can be done all year round
- disease free


- lack of variation
- susceptible to disease – all could die with one disease


2 main techniques: both involve surrogate mothers
(a) early embryos removed from the uterus of cow/sheep and deliberately split into a
number of parts
- each part can be inserted into the uterus of a surrogate mother and will develop
- products as if “identical” twins – since they were divided from the same embryo

(b) an unfertilised egg is removed from the ovary and its nucleus is removed
- the nucleus is replaced by a “normal” body cell
- this is then implanted into a surrogate mother
- product will be genetically identical to the organism from which the implanted
nucleus was derived.