How DNA works

DNA is a biopolymer of deoxyribonucleic acids (a type of nucleic acid) that has four different chemical groups, called bases: adenine, guanine, cytosine, and thymine. It is a substance in living beings which determines their form, and can be used to uniquely identify a person.

The magic of DNA is that the pattern of bases along the strands controls how amino acids join together to make proteins. The pattern of bases along a strand of DNA determines the number, sequence and type of amino acid in the protein. Here is an outline of how this happens:

Manufacture of messenger RNA;
The two strands of DNA contained in the chromosomes of a cell unzip along part of their lenght. Every pattern of three bases along a strand acts as a code for an amino acid. Each pattern of three is a codon. There are 64 codons,but only 20 amino acids,so several codons code for the same amino acid. In addition, there are codons that control the place where the coding starts and stops.
The chain of amino acids that combine along the length of the DNA strand makes a second chain of nucleotides. This new chain is messenger RNA(mRNA).
mRNA has a different order of bases along its length than the original DNA. However, the important thing is that the structure of the mRNA,including the order of bases along its strands,is determined by the DNA.

RNA passes on information to make proteins;
mRNA can pass into the cytoplasm of a cell. Here it attaches itself to small structures called ribosomes. Once joined to the ribosomes, we have ribosomal RNA. Yet another type of RNA in cells, called transfer RNA(tRNA),binds to ribosomal RNA. Each molecule of tRNA carries with it a single amino acid. Now, the bases along the length of ribosomal RNA act as a code for different types of tRNA. This means that along the length of ribosomal RNA gather the various tRNA molecules, each with its own particular amino acid on the end.

Amino acids on transfer RNA form peptide links;
The amino acids are so close together that they join by making peptide links. As this happens,the tRNA minus its amino acid leaves the surface of the ribosomal RNA. The length of the peptide chain increases until one of the codons on the ribosomal RNA does not code for a tRNA with an amino acid. If,as is usually the case,the chain is very long,it wraps round to give a fibrous or globular structure.


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