How do Genes Function? How is a Phenotype Produced?: 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 job done in cytoplasm through their managers – RNAs.
R N A
RNA is ribonucleic acid (Fig 17.8). 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:
1. RNA has ribose instead of deoxyribose
2. RNA has uracil instead of thymine
3. RNA is a single polynucleotide strand, but DNA is made up of two polynucleotide strands.
4. RNA is found throughout the cell but DNA is concentrated in the nucleus.
5. 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):
1. 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 is called transcription. Translation is decoding of mRNA information into a sequence of amino acid in a protein.”
2. 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.