The genes of an individual is the genotype, and the expression of genes results in the phenotype. There are different structural proteins like Haemoglobin in blood, enzymes e.g. pepsin, almost all of which are proteins.

There are carrier proteins in the cell membrane. So there are various proteins and the information for the formation of these proteins is present in the genes.

Central Dogma

Genes are in the nucleus and proteins are synthesized in the cytoplasm of the cell. The transfer of information from genes to the site of protein synthesis constitutes the Central Dogma. Information flows from DNA (particular gene) to the particular protein through RNA.

For protein synthesis, first the information coded in DNA is copied as a complementary messenger RNA molecule. This is termed as Transcription. Messenger RNA carrying information moves out of nucleus into the cytoplasm, attaches to the ribosomes to translate the information in the form of a protein. This is termed Translation.

Genetic Code

The information for the synthesis of proteins is present in the DNA in a sequence of nucleotides. This coded information was discovered by Nirenberg, Mathais and Ochoa.

The genetic code refers to the information in DNA responsible for the amino acid sequence of a particular protein to be synthesized. The information is coded as sequence of nitrogen bases in the DNA molecule. The particular gene or fragment of DNA which carries the code for synthesis of a complete polypeptide (protein) is termed a cistron.