Protein Synthesis
Proteins are made in a living cell as per the information encoded in the genes of the cell. Genes consist of specific sequences DNA in the nucleus of the cell. The genetic code it written in the form of four letters (representing bases) A, T, G, C which stand for Adenine, Thymine, Guanine and Cytosine. This code is read in three letter sets called "codon" which specify the amino acids which get linked to form proteins. The order of base, besides determining the sequence of amino acids is proteins also regulatory commonds. In human beings, a structural sequence or a gene consists of what are called Exons and Introns (fig. no. 28)—that is stretch of utilizable and non-utilizable sequences. The genetic information is translated into proteins directly.
First the entire sequence of bases of DNA are transcribed into RNA as per the base paring rule. Adenine to Thymine, Guanine to cytosine in DNA. In RNA copies of Introns are exercised from the message and all the remaining exons are joined together end to end. The reassembled strand of RNA then moves out of nucleus into cytoplasm when the manufacture of proteins take place. (fig. 34 (a)) What is the quantity of DNA in a human being? A diploid human cell contains 7.3 x 10-12 (with a range of 6.6 to 8.0) with 7.1 x 109 nucleotide pairs. About 6-7 million genes are accommodated on this DNA. 42% of DNA in the human genome consists of repetitive sequences of redundant DNA—that is non coding DNA. Also interspersed with coding DNA is non coding DNA. | |
Fig.34a |