How do genes function? Every phenotype is based on specific biochemical molecules, e.g.; proteins. These proteins are made in the cells under the instructions of genes. Genes sit like a ‘Boss’ seated comfortably on chromosomes in their office – the nucleus. They get their hob done in cytoplasm through their managers – RNAs.
RNA
RNA is ribonucleic acid (Fig17.8). It is also a polynucleotide but its basic unit is ribonucleotide. A ribonucleotide consists of a phosphate group, Ribose sugar and a nitrogenous base. Its four bases are adenine (A), guanine (G), cytosine (C) and Uracil (U). DNA controls synthesis of RNA.
RNA is slightly different from DNA:
Fig.17.8 Structure of RNA
- RNA has ribose instead of deoxyribose
- RNA has uracil instead of thymine
- RNA is a single polynucleotide strand, but DNA is made up of two polynucleotide strands.
- RNA is found throughout the cell but DNA is concentrated in the nucleus.
- RNA is of three types: messenger RNA (mRNA) transfer RNA (tRNA) and ribosomal RNA (rRNA) but DNA has no such types.
A gene expresses itself in two steps (Fig 17.9):
Transcription: the coded information in DNA, which is there in the form of base sequence, is copied into the base sequence of messenger RNA.
Copying of DNA-encoded information into RNA-encoded information called transcription. Translations decoding of mRNA information into a sequence of amino acid in protein.
Fig. 17.9 Genetle Information flows DNA to Protein through mRNA
Translation: the messenger RNA’s message is for the protein synthesis. Its base sequence is translated into a sequence of amino acids of a particular protein.