Saturday, 17 March 2012

5.20 Cloned transgenic animals

Evaluate the potential for using cloned transgenic animals, for example to produce commercial quantities of human antibodies or organs for transplantation.

Animals which are cloned are genetically identical and transgenic refers to an organism having DNA from two or more organisms.

Commercial production of antibodies (example using transgenic cows):

  1. We want to obtain an egg cell from the cow, and from a human we will take a cell and we are going to remove using restriction enzymes we are going to cut a gene associated with antibody production. 
  2. In the egg cell we knock out the cow antibody gene and then we are going to add the human gene using ligase enzyme. 
  3. The cow cell is then developed by mitosis to form clone of cells - an embryo. 
  4. This is transferred to a surrogate mother which will then produce genetically identical calves and in this particular example, the gene for antibodies is expressed and the human antibodies are collected from the milk of the animal in a large commercial scale.

5.19 Mammal Cloning

Describe the stages in the production of cloned mammals involving the introduction of a diploid nucleus from a mature cell into an enucleated egg cell, illustrated by Dolly the sheep

The original sheep in which the scientists take the genetic information from would have the same genes as its clone (Dolly).  This is done by:
  • Removing a diploid cell with the full set of genetic information. This nucleus contains all the genetic information to form a clone.
  •  At the same time, we need to obtain a cell, which has a tendency to divide, so another sheep would be injected with hormones to produce eggs, but we don't want the genetic information so we remove it (enucleation). 
  • So we take the cell with the genetic information that we do wish to copy and we take the egg cell which divides and we fuse them together and by doing so we combine the genetic information that we want with a cell that needs to divide
  • The combination of the two results in many cell divisions by mitosis and forms a ball of cells called the blastula, and this is essentially an embryonic sheep
  • This embryo is placed into another sheep - the surrogate sheep.
  • The embryo will grow into a foetus and then it will be born and this sheep that is born is called Dolly and it has the same sets of genetic information as the first sheep

Sunday, 11 March 2012

5.18 Commercial Plant Growing

Understand how microprogation can be used to produce commercial quantities of identical plants (clones) with desirable characteristics.

If a plants has commercially desirable characteristics, people would want to make many copies of it, however, the two ways of doing this:

  • Sexual reproduction will lead to variation and a loss of qualities. 
  • Therefore, we want to use cloning technique (micropropagation) so that we get many plants of the same quality and commercially that keeps the product the same so it can be sold.

5.17 Micropropagation

Describe the process of micropropagation (tissue culture) in which small pieces of plants (explants) are grown in vitro using nutrient media.

We begin with a plant which has characteristics that we consider desirable and we want to produce more plants of the same kind, the problem is if we use sexual reproduction, the plant will show genetic variation, instead we will have to cloning technique called micropropagation.

  1. We begin by taking tissue from the shoot tip or the root tip 
  2. The next step is under aseptic conditions (free from contamination), we are going to cut this tissue into many small parts
  3. Then transfer the tissue to a petri dish which will contain nutrient agar.
  4.  In addition to the minerals, there will also be rooting compounds and other plant hormones which will encourage the growth of each of the small parts into small clone of the original plant and then each of these can be then grown on into a seedling.
  5.  In the process of doing so, we create a lot of copies of the original plants, and these plants are known as 'clones' which will have the same genes.

5.16 Transgenic Organism

Recall that the term 'transgenic' means the transfer of genetic material from one species to a different species.

The previous objectives 5.13 and 5.15 both show examples of transgenic organisms:

  • In 5.13, the bacterial cell had become transgenic since it still had bacterial DNA but also plasmids that carried human insulin genes.
  • In 5.15, the maize had  become transgenic since we introduced the BT gene to the maize DNA.

Saturday, 3 March 2012

5.15 Genetically Modified Plants

Evaluate the potential for using genetically modified plants to improve food production. (illustrated by plants with improved resistance to pests)

In this example, we will use the crop maize:

  • Maize is damaged by the larvae of the european corkborer and can cause up to 20% loss of crop yield.
  • The bacterial Bt has a chromosome which contains a gene which produces Bt toxin and is known to kill the cork borer larvae.
  • The first step is to take the restriction enzyme to the gene of the Bt bacterium and chop the gene out so we have the Bt gene for the toxin, this is then transferred to the cells of the maize plants.
  • The technique involves the process which is known as 'gene gun' which involves taking tiny particles of gold and coated in the Bt gene, which is fired at high velocity at the plant cell and introduces the Bt gene to the interior of the plant cell.
  • So the plant cell gets the genes, so the maize cells have the Bt genes and means when it is switched on it produces the Bt toxin and kills the pests (larvae of cork borer) and increases crop yield

5.14 Humulin

Understand that large amounts of human insulin can be manufactured from genetically modified bacteria that grow in a fermenter.

  • The bacterial cell containing the recombinant DNA with the human genes (in this case the production of insulin) can be injected into a fermenter and will be necessary to provide it with nutrients, control the temperature and pH and also the gases. 
  • By creating the optimal temperature for bacterial growth, we will see population increase and see the bacteria manufacture protein insulin. 
  • The bacteria inside the fermenter will manufacture the insulin protein from the nutrient (amino acids) provided in the fermenter and it will be necessary to remove the product and carry out purification (called downstream processing) for human usage.
  • The genetically engineered human insulin is called humulin

5.13b Hosting recombinant DNA

Describe how plasmids and viruses can act as vectors, which takes up pieces of DNA, then insert this recombinant DNA into other cells.

  1. After the recombinant DNA is formed, it is necessary to find a host cell for it. In this instance, we will use the virus to achieve this.
  2. We have to remove the nucleic acid from the virus, leaving us with the capsid of the virus alone.
  3. The plasmids are taken up by the virus and the virus will act as a vector of the recombinant DNA.
  4. It will help us transfer that DNA to our host cell, the virus known as a phage infects bacterial cells, and so the virus is able to attach to the cell membrane of the bacteria and insert the recombinant DNA into our host cell.
  5. At the end of this process, we will have a bacteria containing the recombinant DNA including the human DNA for insulin

5.13a Recombinant DNA

Describe how plasmids and viruses can act as vectors, which take up pieces of DNA, then insert thiis recombinant DNA into other cells.

Plasmids are find in bacterial cells and are a ring of DNA and are particularly small carrying little DNA.

Viruses have a protein shell called a capsid and inside there would be a Nucleic acid (of which contains either DNA or RNA).

The human chromosome is made of DNA and in our example, we will talk about the gene which codes for the production of the protein, insulin (hormone controlling blood sugar levels).

  1. The restriction enzyme would be selected to cut the DNA, leaving us with the gene of insulin separately.
  2. Having cut the gene, the plasmid will also be cut with the same restriction enzyme.
  3. This leaves the plasmid ring structure broken, the human insulin gene is then inserted into the plasmid.
  4. This will leave our plasmid with the human gene inserted and is then necessary to apply ligase enzyme which will join the DNA.
  5. This combination of the human gene, and the plasmid is known as recombinant DNA.

5.12 Restriction and Ligase Enzymes

Describe the use of restriction enzymes to cut DNA at specific sites and ligase enzymes to join pieces of DNA together.

  1. The restriction enzyme is able to cut the DNA, the restriction enzyme cuts the DNA at a particular location, and this location is identified by the base sequence
  2. The ligase enzyme is able to join the two pieces of DNA together.

These are commonly used with genetical engineers and bio engineers.