What makes us “us”? What is responsible for producing startling inherited resemblances between the members of a family as well as distinctive variations in different generations? Why are identical twins so ‘identical’? Why do some diseases tend to run in families?What causes diseases like cancer, diabetes , AIDS and Alzheimer’s so difficult to cure? How is production of clones possible? These questions can all be answered by genetics, so here’s the introduction to genetics.

“Genetics” presents answers to all those and hundreds of other curious questions. From understanding the variations in eye color to the new principles of Biotechnology, Genetics is full of interesting concepts.In simple,Genetics deals with the study of the units of inheritance called “Genes”.

To understand what a Gene is, first we must be familiar with the structure and function of the DNA, because Genes are the working subunits of DNA. Basically, Genes are the codes of the biological information that builds and maintains body’s structure and function and is also transferred to the offsprings of any organism. This article specifically focuses on the most basic concept of Molecular Genetics i.e DNA.

Introduction To Genetics: The Molecular Basis Of Life ‘DNA’

DNA or Deoxyribonucleic Acid is the basic unit of heredity in every organism. Discovered in 1869 by Chemist Friedrich Miescher,  there was a very little research on understanding its structure and role in cell,for the next 50 years.

In 1920,structure of DNA was revealed. DNA is acidic in nature present in the nucleus of the cell. It has 3 chemical components.A five carbon sugar, a nitrogen base and a phosphate group. There are four Nitrogen bases of two types,large ringed called Purines and small ones known as Pyrimidines. Adenine and Guanine are Purines and Cytosine and Thymine are Pyrimidines. Each purine forms Hydrogen bonds with a pyrimidine. Adenine forms two H-bonds with Thymine, while Cytosine and Guanine form three bonds. The sequence of these base pairs determines the sequence of protein sub-units called Amino acids. Each base is attached to a five carbon ribose sugar(at carbon 2 two H are present instead of one H and one OH group) and a Phosphate group. This whole structure is known as a “Nucleotide”.

The sequence of nucleotides that determines the amino acid sequence of a protein is called a “Gene”.  Nucleotides are arranged in Double Helix, with the base pair of two strands pointed inwards towards each other while the sugar and Phosphate form the “Backbone” of the Helix.

Almost all cells in a person’s body has the same DNA. Only in sex cells or Gametes the DNA is half of the rest of the cells of the body. Human DNA has about 3 million base pairs and 99% of all DNA is similar in all humans, whereas identical twins have 100% same DNA. The DNA and proteins are coiled to form a Chromosome. The number of Chromosomes is same in all individual of a species.

Humans have 46 chromosomes arranged in 23 pairs. A typical Human Chromosome contains about 140 million nucleotides in its DNA. The amount of Genetic information present on one chromosome would fill about 280 printed books of 1000 page, if each nucleotide corresponds to one word and each page had 500 words on it.  A DNA strand of Chromosome is 5 cm on average and human body on average has 10 Trillion cells, which would mean that if your DNA is stretched out, it would equal about 744 million miles and would reach sun and back about 600 times!

Most interesting thing about the DNA is that 98.5% of it is never used, it does not encode of any proteins. This “Junk DNA” became accumulated throughout Evolution. The DNA similarities between different organisms are marvelous. 8% of our DNA resembles that of Chimps, 90% to yeasts, 50% to the DNA of Cabbage and Bananas, 1% to sunflowers’ and 223 genes in our DNA resembles that of Bacteria, means we eat DNA everyday!

DNA replicates just before cell division so that all cells get the same DNA. DNA is a Marvel of Nature. It might have been the first molecule that made LIFE possible.

[Image Credit: Caroline Davis2010 (Creative Commons) | flikr ]