Structure of DNA
DNA is a store of genetic information which is important for synthesis of polypeptides in a cell, cell differentiation and cell division. A segment of DNA that codes for a specific sequence of amino acids on a polypeptide chain is known as the gene. DNA associates with histone proteins to form a chromatin thread. Chromatin thread further coils around itself to form a chromosome.
The basic unit of DNA is a nucleotide that consists of a five carbon sugar known as deoxyribose, a nitrogenous base (adenine, thymine, guanine or cytosine) and a phosphate group. Nucleotides join together to form a polynucleotide. Two strands of polynucleotides run in opposite directions and are held by hydrogen bonds between complementary base pairs to form a DNA molecule. Complementary base pairing involves adenine on one polynucleotide strand base pairing with thymine on the opposite polynucleotide strand. Guanine on one polynucleotide strand base pairing with cytosine on the opposite polynucleotide strand.
Protein Synthesis
Every three nucleotides on the gene codes for one amino acid. Different combinations of nucleotides on the gene would code for different sequence of amino acids on the polypeptide chain. Synthesis of polypeptide involves two main processes - (i) transcription and (ii) translation.
During transcription at the nucleus, the template DNA strand is read and used to make the messenger RNA (mRNA) by complementary base pairing. mRNA then moves from the nucleus and binds to ribosomes where every triplet bases on the RNA nucleotides are read and translated to form amino acids on the polypeptide chain.
Genetic engineering
Genetic engineering refers to identifying, isolating, inserting and transferring the gene of interest from one organism to another organism. The organism receiving the gene of interest may be of the same or different species. The recipient organism would express the transferred gene. The gene of interest has to be inserted into a DNA vector. The DNA vector discussed is the plasmid which is obtained from a bacteria.
Advantages of genetic engineering would be the ability to increase crop yields, reduced costs for food or drug production, reduced need for pesticides, ability to improve nutritional qualities, resistance to diseases, synthesis of potential medicinal cures and increase animal production by inserting the growth hormone gene into targeted livestock such as salmon.
There are concerns on genetic engineering such as use of pesticides, herbicides or antibiotic resistance may cause specific species in the ecosystem to be removed and this causes instability in the food chains and food webs. Other concerns include the possible presence of new allergens in genetically modified foods. Introduction of a foreign gene into another organism may also affect its growth rate, metabolism and response to external environmental factors that may affect the transgenic organism as well as the environment.