DNA structure, function, and biological significance

DNA or deoxyribonucleic acid is the only commonly found molecule that can dictate its own syntheses through reproduction, for this reason the DNA is the cell structure that dictates genetic material to a new organism. (Carter, 2004, NP) the shape and form of DNA create the ability of it to regenerate in patterned sequences, that are limitedly predictable and there fore result in a new genetic identity, with many of the existing organism's characteristics and some from a new organism, also supplying DNA to the process.

DNA forms as a double helix with the outer and inner edges forming alternating ladders and rungs that determine the function of the DNA at given periods of reproduction, through the chemical representation of cell formation:

The outer edges are formed of alternating ribose sugar molecules and phosphate groups. The two strands go in opposite directions (1 "up" and 1 "down"). The nitrogenous bases are "inside" like rungs on a ladder. Adenine on one side pairs with thymine (uracil in RNA) on the other by hydrogen bonding, and cytosine pairs with guanine. Note that the C-G pair has three hydrogen bonds while the a-T pair has only two, which keeps them from pairing wrong. This dictates side-to-side pairing, but says nothing about the order along the molecule. Watson and Crick said this variability along the molecule can account for the variety in the genetic code. Their model also accounts for how DNA can replicate itself. They said the molecule "unzips" and new matching bases are added in to create two new molecules. They called this semiconservative replication because each new molecule has one "old" and one "new" strand of DNA. (Carter, 2004, NP)

As a result of this DNA replication process it serves as the main road map for the development of new cells with both old and new characteristics.

DNA codes for protein synthesis by first coding for RNA. First, the DNA code is transcribed to RNA code, which is still in the "language" of nitrogenous bases, except that adenine on the DNA pairs with uracil (in place of thymine) on the RNA. The RNA code is then translated to protein code, which is a different "language." This process involves ribosomes and two kinds of RNA: mRNA and tRNA. The mRNA codes for the gene in question and is copied off the DNA, while tRNA matches a specific group of nucleotides with a specific amino acid. A "unit" of three nucleotides on the tRNA codes for one amino acid. Each of these "units" is called an anticodon. These match up with corresponding three-nucleotide sequences on the mRNA called codons, and in this manner the amino acids are organized into the correct sequence to build a protein. The ribosome works with the mRNA and tRNA to hook the amino acids together to form a protein. (Carter, 2004, NP)

The replication structure of DNA serves as a basis for inheritance through the development of meiosis which allows gene pairs to form into a new organism, based on the determining genome factors of the original cells.

The blueprint for what every one of us will be like appears at the instant in which the gametes of our father and mother merge to form a single whole, called the zygote or the fertilized egg. The entire message is encapsulated in the nucleus of this single cell -- more precisely, in its DNA molecule. This molecule carries information about the color of our eyes and hair, about our stature, the form of our nose, whether or not we will be a virtuoso musician, and many other things. Of course, our future depends not only on DNA but also on the unpredictable vicissitudes of life. However, many, many thing in our individual destiny will be determined by the qualities built into us at birth by our genes -- that is, by the sequence of nucleotides in our DNA molecules. (Frank-Kamenetskii, 1997, p. 27)

This pairing, will determine the nature of the final being, which will then be affected by its environment to some degree with the inclusion of predisposition of the genetic forms. Gametes, or reproductive cells contain the given and donated DNA. Once the DNA structure creates a reproductive event the gametes then translate this information into a complete being with characteristics of both donors.

There are two categories of cells in multicellular organisms based on their chromosomes: Somatic (another word for "body" cells) and Gametes (reproductive cells). In human gametes, each sperm cell has 23 chromosomes, and each egg cell has 23 chromosomes through the process of Meiosis. This is called the haploid number and is represented by the letter n. When these two gametes get together, they form a complete human whose somatic cells have 46 chromosomes. This is the diploid number and is represented by 2n. (Petty, 2005, NP)