After the initiation phase the message gets longer during the elongation phase. The complex then shifts along the mRNA to the next triplet, opening the A site. The new tRNA enters at the A site. In this way a cell may rapidly make many proteins. Addition, deletion, or addition of nucleotides can alter the polypeptide.
Point mutations are the result of the substitution of a single base.
Frame-shift mutations occur when the reading frame of the gene is shifted by addition or deletion of one or more bases. With the exception of mitochondria, all organisms use the same genetic code. Powerful evidence for the common ancestry of all living things. Slideshow and downloadable animation of the process. A text with links to illustrations.