Chemical concept

12.6 Process of Genetic Engineering

CONCEPT

As mentioned in the introduction, genetic engineering is the alteration of genetic material by direct intervention in genetic processes with the purpose of producing new substances or improving functions of existing organisms. On one hand, it offers the possibility of cures for diseases and countless material improvements to daily life. Hopes for the benefits of genetic engineering are symbolized by the Human Genome Project, a vast international effort to categorize all the genes in the human species. On the other hand, genetic engineering frightens many with its potential for misuse, either in Nazi-style schemes for population control or through simple bungling that might produce a biological holocaust caused by a man-made virus. Symbolic of the alarming possibilities is the furor inspired by a single concept on the cutting edge of genetic engineering: cloning.

Any discussion of genetics makes reference to DNA (deoxyribonucleic acid), a molecule that contains genetic codes for inheritance. DNA resides in chromosomes, threadlike structures found in the nucleus, or control center, of every cell in every living thing. Chromosomes themselves are made up of genes, which carry codes for the production of proteins. The latter, of which there are many thousands of different varieties, make up the majority of the human body’s dry weight.

 

HOW IT WORKS

DNA was discovered more than 130 years ago in 1869 by Swiss biochemist Johann Friedrich Miescher (1844-1895). He isolated a substance, containing both nitrogen and phosphorus, that separated into a protein and an acid molecule and called it nucleic acid. In this material he discovered DNA. In 1944, a research team led by the Canadian-born American bacteriologist Oswald Avery (1877-1955) found that by taking DNA from one type of bacterium and inserting it into another, the second bacterium took on certain traits of the first. This experiment, along with other experiments and research, proved that DNA serves as a blueprint for the characteristics and functions of organisms.

 

THE DOUBLE HELIX

Nine years later, in 1953, the American biochemist James D. Watson (1928-) and the English biochemist Francis Crick (1916-) proposed a double helix, or spiral staircase, model, which linked the chemical bases of DNA in definite pairs. Using this twisted-ladder model, they were able to explain how the DNA molecule could duplicate itself, since each side of the ladder is identical to the other; if separated, each would serve as the template for the formation of its mirror image. This is known as the semi-conservative replication. 

The sides of the DNA ladder are composed of alternating sugar and phosphate molecules, like links in a chain, and consist of four different chemical bases: adenine, guanine, cytosine, and thymine. The four letters designating these bases—A, G, C, and T—are the alphabet of the genetic code, and each rung of the DNA molecule is made up of a combination of two of these letters. Owing to specific chemical affinities, A always combines with T and C with G, to form what is called a base pair. Specific sequences of these base pairs, which are bonded to each other by atoms of hydrogen, constitute the genes.

Image taken from Google

PRINCIPLES OF GENETIC ENGINEERING

Just as DNA is at the core of studies in genetics, recombinant DNA (rDNA)—that is, DNA that has been genetically altered through a process known as gene splicing —is the focal point of genetic engineering. In gene splicing, a DNA strand is cut in half lengthwise and joined with a strand from another organism or perhaps even another species. Use of gene splicing makes possible two other highly significant techniques. Gene transfer, or incorporation of new DNA into an organism’s cells, usually is carried out with the help of a microorganism that serves as a vector, or carrier. Gene therapy is the introduction of normal or genetically altered genes to cells, generally to replace defective genes involved in genetic disorders.

DNA can also be cut into shorter fragments through the use of restriction enzymes. (An enzyme is a type of protein that speeds up chemical reactions.). Restriction enzymes are synthesised naturally in bacteria which protect them from viruses by degrading incoming viral DNA . Each restriction enzyme recognises a specific sequence of 4 to 8 nucleotide bases on the DNA molecule known as restriction site. It acts like a molecular scissors, cutting up DNA molecules into fragments called restriction fragments.

The ends of these fragments have an affinity for complementary ends on other DNA fragments and will seek those out in the target DNA. By looking at the size of the fragment created by a restriction enzyme, investigators can determine whether the gene has the proper genetic code. This technique has been used to analyze genetic structures in fetal cells and to diagnose certain blood disorders, such as sickle cell anemia.

Image taken from Google

HOW IT WORKS TO PRODUCE GMO:

  1. Identify a trait of interest
    For example,  to improve the nutritional content of a crop, researchers would have to screen a list of plants that they hypothesize produce the nutrient of interest.
  2. Isolate the genetic trait/gene of interest (GOI)
  3. Insert the GOI into a new genome. This is done by:Extraction of plasmid (a small, circular DNA) from the bacteria or yeast cell.
    Desired genetic trait and plasmid are cut with same restriction enzymes.
    GOI is inserted into the gap in the plasmid. This is known as the recombinant DNA.
  4. Growing the GMO
    After the GOI has been successfully inserted into an organism’s genome, the modified organism must be able to grow and replicate with its newly engineered genome.
    The genotype of the organisms must be checked so that only organisms in which the genome was modified correctly are propagated.

Image taken from http://sitn.hms.harvard.edu/flash/2015/how-to-make-a-gmo/

 

References:

www.yourgenome.org

How to Make a GMO

CM8001 Group 18

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