When a ribosome encounters a stop codon, it dissociates from the mRNA through the enzymatic action of release factors. These are UAA, UAG and UGA and are recognized by proteins called release factors rather than by tRNAs. Out of the 64 codons made by various combinations of 4 nucleotides, 3 are stop codons, that signal the end of translation. This degeneracy is aided by the fact that the third nucleotide in every codon binds loosely to its corresponding tRNA, allowing unusual types of bases to pair with each other. Similarly, phenylalanine can be represented by either UUU or UUC on the mRNA and leucine is coded by a total of six codons. For instance, the amino acid serine can be coded by six codons of which four are: UCA, UCG, UCU or UCC. Often, the difference between degenerate codons is the third base which is called the ‘wobble position’. In addition, since stretches of 3 nucleotides can give rise to a total of 64 codons, a single amino acid can be coded by multiple codons, a property that is called ‘degeneracy’.
TRANSCRIBE BIOLOGY SERIES
A series of experiments in the 1960s confirmed this hypothesis and also showed that these codons do not overlap with each other. Therefore, it was suggested that amino acids were coded by stretches of three nucleotides called codons.
TRANSCRIBE BIOLOGY CODE
Even having two nucleotides code for a single amino acid is insufficient. Therefore, it is not possible to have a direct one-to-one correlation between the sequences of nucleotides and amino acids. There are only 4 bases in nucleic acids whereas proteins are made of 20 amino acids. When nucleic acids were discovered as the primary genetic material, one important question came to the fore. Ribosomes and tRNA dock on a mature mRNA transcript and recruit multiple enzymes in an energy intensive process that uses ATP as well as GTP. The sequence of nucleotides on the RNA is translated into the amino acid sequence of proteins and this reaction is carried out by ribosomes. Translation refers to the process of creating proteins from an mRNA template.
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