The original transcript from the DNA is called pre-mRNA. It contains transcripts of both introns and exons. The introns are removed by a process called splicing to produce messenger RNA (mRNA). Ribozymes are catalytic RNA molecules that function as enzymes and can splice RNA. RNA splicing removes introns and joins exons. RNA Splicing can also be carried out by spliceosomes. How is it possible that there are millions of human antibodies when there are only about 30,000 genes? Alternative splicing refers to the different ways the exons of a gene may be combined, producing different forms of proteins within the same gene-coding region. Alternative pre-mRNA splicing is an important mechanism for regulating gene expression in higher eukaryotes. Proteins often have a modular architecture consisting of discrete structural and functional regions called domains. In many cases different exons code for the different domains in a protein. Translation is the RNA-directed synthesis of a polypeptide. Translation involves :mRNA. Ribosomes - Ribosomal RNA. Transfer RNA, Genetic coding – codons. Genetic information is encoded as a sequence of nonoverlapping base triplets, or codons. The gene determines the sequence of bases along the length of an mRNA molecule. Codons: 3 base code for the production of a specific amino acid, sequence of three of the four different nucleotides. Since there are 4 bases and 3 positions in each codon, there are 4 x 4 x 4 = 64 possible codons. 64 codons but only 20 amino acids, therefore most have more than 1 codon. 3 of the 64 codons are used as STOP signals; they are found at the end of every gene and mark the end of the protein. One codon is used as a START signal: it is at the start of every protein.
To be continued.........