Description of Genomes
Most genomes, including those for all cellular lifeforms, are made of DNA(deoxyribonucleic acid), and some have RNA(ribonucleic acid). DNA and RNA are polymetric molecules made up of linear, unbranched chains of monometric subunits called nucleotides. Each nucleotide has 3 parts: a sugar, a phosphate grop and a base.
Description of Bases
Bases have 4 types: Adenine, Thymine, Cytosine, Guanine, also well-known as A,T,C,G. They hold the polynucleotides by means of hydrogen bonds between another. As you already know, A pairs with T, C pairs with G.
Structure of DNA
Each deoxyribonucleotide consists of sugar 2'-deoxyribose linked to a phosphate group and 1 base. Nucleotides are linked together by phosphodiester bonds to give a polynucleotide, the 2 ends which are chemically different. In the double helix, 2 polynucleotides, running in different directions, are wound around one another and held by base bonds.
Description of the Human Genome
The Human Genome is made of 2 distinct parts:
It comprises of nearly 3 000 000 000 base pairs of DNA.They are divided into 24 linear DNA molecules, the shortest 55 Mb (megabase-pairs) long and the longest 250 Mb, each one in a different chromosome. There are 22 autosomes and 2 sex chromosomes, X and Y.
A circular DNA molecule of 16 569 bp, many copies of which are located in the energy-generating organelles called microchondria.
Interesting facts about RNA
There are 3 types of RNA:
1)Messenger RNA (mRNA)/ Coding RNA
This is the only form of RNA that gets translated, as it contains information needed to make amino acids.
Ribosomal or rDNA are components of ribosomes, the structures on which protein generation takes place. Tranfer or tRNA, small molecules involved in protein generation, carrying amino acids to the ribosome and ensuring these are linked together in the order specified by the nucleotide sequence of the mRNA that is being translated.
Mapping by genetic markers
There are 3 ways of doing this:
1) Restriction fragment length polymorphisms (RFLPs)
This involves the use of restriction endonuclease, which is a chemical that cuts DNA molecules at definite sequences.
2) Simple sequence length polymorphisms (SSLPs)
These are arrays of repeated sequences, different stretches containing different number of repeats.
3) Simple nucleotide polymorphisms (SNPs)
The explanation of THIS one is going to blow your mind. These are individual point mutations. There are a vast number of these; there are thought to be over 200,000 SNPs that lie in genes. This method is more rapid as it is based on oligonucleotide hybridization analysis. Am oligonucleotide is a short, single-stranded DNA molecule, usually less than 50 nucleotides in length, that is synthesised in the test tube. Under the right conditions it will hybridize with another DNA molecule only if the oligonucleotide forms a complete base-paired structure with the second molecule. Screening is done via
1)DNA chip, where the test DNA, with a flourecent marker, is pipetted onto a chip with many different oligonucleotides in a high density array. The position of the flourecent signal, which can be seen under a flouresence microscope, shows which oligonucleotide the DNA strand has bonded with.
2) Dynamic allele-specific hybridization, consists of the testing DNA with a flourecent marker which binds only when hybridization takes place, a solution of oligonucleotides and a heat source. Hybridization only occurs under conditions that allow bonding despite a mismatch; allele discrimination is achieved by raising the temperature, as increased temperature increases the instability of the bonds, causing de-hybridiation. Which allele is present in the test DNA can therefore be determined from the temperature at which the hybridization-dependant flourecent signal disappears.
Alleles are stretches of bases.
What are Genetically Modified (GM) Foods?
Although "biotechnology" and "genetic modification" commonly are used interchangeably, GM is a special set of technologies that alter the genetic makeup of such living organisms as animals, plants, or bacteria. Biotechnology, a more general term, refers to using living organisms or their components, such as enzymes, to make products that include wine, cheese, beer, and yogurt.
Combining genes from different organisms is known as recombinant DNA technology, and the resulting organism is said to be "genetically modified," "genetically engineered," or "transgenic." GM products (current or in the pipeline) include medicines and vaccines, foods and food ingredients, feeds, and fibers.
Locating genes for important traits-such as those conferring insect resistance or desired nutrients-is one of the most limiting steps in the process. However, genome sequencing and discovery programs for hundreds of different organisms are generating detailed maps along with data-analyzing technologies to understand and use them.
GM crops are grown commercially or in field trials in over 40 countries and on 6 continents. In 2000, about 109.2 million acres were planted with transgenic crops, the principal ones being herbicide- and insecticide-resistant soybeans, corn, cotton, and canola. Other crops grown commercially or field-tested are a sweet potato resistant to a virus that could decimate most of the African harvest, rice with increased iron and vitamins that may alleviate chronic malnutrition in Asian countries, and a variety of plants able to survive weather extremes.
On the horizon are bananas that produce human vaccines against infectious diseases such as hepatitis B; fish that mature more quickly; fruit and nut trees that yield years earlier, and plants that produce new plastics with unique properties.
In 2000, countries that grew 99% of the global transgenic crops were the United States (68%), Argentina (23%), Canada (7%), and China (1%). Although growth is expected to plateau in industrialized countries, it is increasing in developing countries. The next decade will see exponential progress in GM product development as researchers gain increasing and unprecedented access to genomic resources that are applicable to organisms beyond the scope of individual projects.
Technologies for genetically modifying (GM) foods offer dramatic promise for meeting some areas of greatest challenge for the 21st century. Like all new technologies, they also poses some risks, both known and unknown. Controversies surrounding GM foods and crops commonly focus on human and environmental safety, labeling and consumer choice, intellectual property rights, ethics, food security, poverty reduction, and environmental conservation (see below for a summary of "GM Foods: Benefits and Controversies").