DNA makes RNA makes protein
In higher organisms, the hereditary material, DNA,
is located in the cell nucleus.
The DNA in one human cell contains about 100,000 genes, located on 46 chromosomes.
A chromosome pair and the DNA molecule, a long double-stranded helix, are shown to the right and below.
The genetic information in the DNA is stored as a
sequence of bases (or nucleotides). The bases are
stacked in between the two strands which wind
around each other.
The order of the bases determines the genetic information. When a gene is activated, the DNA strands separate and one of them serves as a template for copying a messenger RNA (mRNA) as shown on the right.
The letters represent the bases adenine (A),
thymine (T), guanine (G) and cystosine (C).
In the double helix, A always pairs with T, and C with G. In the mRNA, thymine is replaced by uracil (U).
A stretch of three bases in the mRNA determines the
position of a particular amino acid in the growing
The mRNA, containing the information for a particular protein, is transported from the nucleus to the cytoplasm, where protein synthesis takes place. Amino acids are joined together as pearls on a string.
There are 20 different amino acids. Their order in the protein molecule determines its structure and function. Proteins may serve e.g., as enzymes, hormones or structural components of a cell.
The final protein molecule may