Adaptor hypothesis and discovery of mrna template biology discussion
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Adaptor hypothesis
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The adaptor hypothesis is part of a scheme to explain how information encoded in DNA is used to specify the amino acid sequence of proteins. It was formulated by Francis Crick in the mid-1950s, together with the central dogma of molecular biology and the sequence hypothesis. It first appeared in an informal publication of the RNA Tie Club in 1955 and was formally published in an article “On Protein Synthesis” in 1958.
Explanation
The adaptor hypothesis was framed to explain how information could be extracted from a nucleic acid and used to put together a string of amino acids in a specific sequence, that sequence being determined by the nucleotide sequence of the nucleic acid (DNA or RNA) template. Crick proposed that each amino acid is first attached to its own specific “adaptor” piece of nucleic acid (in an enzyme-catalysed reaction). The order of assembly of the amino acids is then determined by a specific recognition between the adaptor and the nucleic acid which is serving as the informational template. In this way the amino acids could be lined up by the template in a specific order. Coupling between adjacent amino acids would then lead to the synthesis of a polypeptide whose sequence is determined by the template nucleic acid.
Basis
Crick’s thinking behind this proposal was based on a general consideration of the chemical properties of the two classes of molecule — nucleic acids and proteins. The amino acids are characterised by having a variety of side chains which vary from being hydrophilic to hydrophobic: their individual characters reside in the very different properties these side chains have. By contrast, a nucleic acid is composed of a string of nucleotides whose sequence presents a geometrically defined surface for hydrogen bonding. This makes nucleic acids good at recognising each other, but poor at distinguishing the varied side chains of amino acids. It was this apparent lack of any possibility of specific recognition of amino acid side chains by a nucleotide sequence which led Crick to conclude that amino acids would first become attached to a small nucleic acid — the adaptor — and that this, by base-pairing with the template (presumably as occurs between DNA strands in the double helix), would carry the amino acids to be lined up on the template.
Proof
That such adaptors do exist was discovered by Mahlon Hoagland and Paul Zamecnik in 1958. These “soluble RNAs” are now called transfer RNAs and mediate the translation of messenger RNAs on ribosomes according to the rules contained in the genetic code. Crick imagined that his adaptors would be small, perhaps 5-10 nucleotides long. In fact, they are much larger, having a more complex role to play in protein synthesis, and are closer to 100 nucleotides in length.
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Last edited 5 years ago by AdamoulasA
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Adaptor Hypothesis
Explanation:
- The adaptor hypothesis is a piece of a scheme to clarify how information encoded in DNA is utilized to indicate the amino acid grouping of proteins
- Coupling between adjacent amino acids would then prompt the blend of a polypeptide whose arrangement is dictated by the template nucleic acid
- Adapter hypothesis, suggested that small RNA molecules would be the adaptors that could be charged of amino acids by explicit proteins and that could recognize the codons (triplets of nucleotides) of the of the mRNA by base-pairing