3.5 Genetic Modification

Explain the Steps for PCR

Denaturation – DNA sample is heated (\~90ºC) to separate the two strands
Annealing – Sample is cooled (\~55ºC) to allow primers to anneal (primers designate sequence to be copied)
Elongation – Sample is heated to the optimal temperature for a heat-tolerant polymerase (Taq) to function (\~75ºC)

Def: PCR

The polymerase chain reaction (PCR) is an artificial method of replicating DNA under laboratory conditions

Purpose of PCR

The PCR technique is used to amplify large quantities of a specific sequence of DNA from an initial minute sample

Explain how gel electrophoresis can separate protein according to sizes.

* Smaller molecules migrate through the gel more quickly and therefore travel further than larger fragments that migrate more slowly and therefore travel a shorter distance.
* As a result the molecules are separated by size.
* Gel electrophoresis is a technique that separates proteins or fragments of DNA according to size
* Samples placed in a block of gel and current is applied Smaller samples move faster through the gel (low resistance)
* Samples will move towards the positive terminus (anode)
DNA is negatively charged (due to phosphate group)

Explain the steps for somatic cell nuclear transfer.

* Differentiated Cell (somatic cell) taken from adult donor organism
* Cell cultured in low nutrient medium, so active genes shut down
* Cell is now undifferentiated again (like a stem cell) and can be differentiated into any type of cell as it divides and develops
* Nucleus is removed from donor cell
* Unfertilised egg cells is taken from a different animal of same species
* Nucleus of egg cell removed, disposed of -> does not contribute any of it’s own DNA to clone that will develop
* Nucleus from donor cell is then inserted into egg cell, two are fused with electric pulse Egg cell now contains nucleus, DNA of og donor organism -> newly fertilized zygote

What is the difference between reproductive cloning and therapeutic cloning? ( 2 marks)

In therapeutic cloning embryonic cells can be induced to differentiate to create specific tissues or organs for transplantation

while in reproductive cloning if the embryo is implanted into the uterus of a surrogate, a new cloned organism will develop.

Risks of GMO Crops

Some gene transfer may be harmful to the host organism (particularly animals).
Genes could be harmful or allergenic to other organisms, including humans.
Genes could be transferred to other species of organisms that are not the target organism.
GMOs could spread and compete with natural organisms, disrupting ecosystems.

Benefits of GMO Crops

* Could be used to improve nutritional standards
* Can grow in a wide range of environments (higher yields)
* Could reduce farming costs and associated deforestation
* Can be used to reduce spoilage (longer shelf life)

Explain the process of Gene Transfer

\-a plasmid is removed from a bacterial cell;
\-the plasmid is cut using a specific restriction enzyme, leaving sticky ends;
\-a copy of the DNA containing the desired gene is removed from a donor organism;
\-the same restriction enzyme is used to cut the donor DNA into fragments;
\-one fragment contains the desired gene;
\-the gene is introduced into the plasmid;
\-DNA ligase is used to join the gene and plasmid together;
\-forming a recombinant plasmid;
\-the recombinant plasmid is then inserted into a host cell, which will contain the desired gene and express the product of that gene;

Explain one application of Gene Transfer in plants and animals that is useful.

* the gene for the production of human insulin is isolated from human cells;
* and transferred to E. coli bacteria using a plasmid;
* the bacteria incorporate the gene into their DNA;
* they are then are cloned / allowed to reproduce naturally;
* the resulting population all contain the gene and therefore produce insulin;
* the insulin can then be separated and purified, and used to treat patients with diabetes;

Define: genetic modification and identify how it is carried out.

* the transfer of selected genes from one organism to another;
* carried out by gene transfer between species;

What is gene transfer?

when a gene coding for a particular polypeptide and influencing a specific characteristic in an organism of one species is transferred to another organism of a different species

Why can genes be transferred between species but the proteins produced by them remain unchanged?

* because the genetic code is universal;
* all organisms’ DNA contains the same four nucleotide bases: A, T, C, G;
* so when genes are transferred the sequence of amino acids translated from them is unchanged;
* and the same polypeptide is produced;

Outline the role of the restriction enzymes in gene transfer

* cut DNA at specific base sequences;
* leaving sticky ends that can be used to join together the gene and plasmid;

Outline the role of DNA Ligase in gene transfer

* joins the gene and plasmid together;
* by forming covalent bonds between the sugars and phosphates in the DNA backbone;

Summarize the steps involved in gene transfer using plasmids.

* a plasmid is removed from a bacterial cell;
* the plasmid is cut using a specific restriction enzyme, leaving sticky ends;
* a copy of the DNA containing the desired gene is removed from a donor organism
* the same restriction enzyme is used to cut the donor DNA into fragments
* one fragment contains the desired gene
* the gene is introduced into the plasmid
* DNA ligase is used to join the gene and plasmid together; forming a recombinant plasmid
* the recombinant plasmid is then inserted into a host cell, which will contain the desired gene and express the product of that gene;

Outline the process by which human insulin is produced using gene transfer.

* the gene for the production of human insulin is isolated from human cells;
* and transferred to E. coli bacteria - using a plasmid;
* the bacteria incorporate the gene into their DNA;
* they are then are cloned / allowed to reproduce naturally;
* the resulting population all contain the gene and therefore produce insulin;
* the insulin can then be separated and purified, and used to treat patients with diabetes;