DNA and Chromosomes

DeoxyriboNucleic Acid is commonly known as DNA. DNA at its most basic level is in essence the blueprint of an organism's genetic make-up. The shape of DNA, discovered by Francis Crick and James Watson, is a double helix. The composition of DNA is a series of nitrogenous bases (known as base pairs), and sugar and phosphate strands. Within the ladder model of DNA (at left), the sugar and phosphate strands compose the sides of the DNA model, or molecule, while the actual rungs of the ladder are made up of the 4 nitrogen bases. For a molecule of DNA to maintain its shape there are a number of rules between pair bonds, and the strands of phosphates. They are as follows:

(Please note this is an oversimplification)

• The four pair bonds, Cytosine, Guanine, Adenine, and Thymine, do not entirely intermix. Only Cytosine can attach with Guanine, and only Adenine can attach to Thymine. Or only C's can attach to G's, and only T's to A's.

• The Phosphate and Sugar strands (edges of the ladder), are arranged as follows, S - P - S - P - S - P, etc.

In the composition of DNA, codons are a grouping of three base pair sequences, which determine the production of different types of amino acids. There are 20 different types of amino acids, which a cell uses to produce proteins, and which are central to the functioning of cells within an organism. Even the most minute differentiation in the amount and type of amino acid, can have drastic effects on a cell's composition and function.

DNA replicates itself by splitting itself in two, or unzipping itself like a zipper. Once detached, the split side of the ladder connects with free floating nucleotides (C, T, A, and G base pairs). Connections between Nucleotides are governed by the base pair rule( i.e. C's can only connect with G's, and T's can only connect with A's). When replication is complete, two identical strands of DNA are produced.

Chromosomes

Cells, whether through meiosis or mitosis, share genetic information through chromosomes. Chromosomes are the package for DNA and genes. A living organism has roughly 5 feet or 1.5 meters of compacted DNA within it's nucleus. To contain the DNA within the nucleus of a cell, the genetic information is wound up into strands like coiled rope. These strands take the shape of X's. Each place on a chromosome holds genetic information which pertains to the expression of a trait. The genetic information a chromosome holds, or one piece of genetic information a chromosome can hold, is known as a gene. An allele is a point or place on a chromosome. The locus is a place on a specific chromosome where a gene is found.

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