Wobble Hypothesis

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The Wobble Hypothesis, by Francis Crick, states that the 3rd base in an mRNA codon can undergo non-Watson-Crick base pairing with the 1st base of a tRNA anticodon <ref>Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. (2008) Molecular Biology of The Cell, 5th edition, New York: Garland Science.</ref>&nbsp;
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The Wobble Hypothesis, by Francis Crick, states that the 3rd base in an mRNA codon can undergo non-Watson-Crick base pairing with the 1st base of a tRNA anticodon <ref>Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. (2008) Molecular Biology of The Cell, 5th edition, New York: Garland Science.</ref>&nbsp;  
  
The mRNA codon’s first 2 bases form Hydrogen bonds with their corresponding bases on the tRNA anticodon in the usual Watson-Crick manner, in that they only form base pairs with complimentary bases. <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref> However, the formation of Hydrogen bonds between the 3rd base on the codon and the 1st base on the anticodon can potentially occur in a non-Watson-Crick manner. Therefore different base pairs to those usually seen can form at this position.&nbsp;<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>&nbsp;
+
The mRNA codon’s first 2 bases form Hydrogen bonds with their corresponding bases on the tRNA anticodon in the usual Watson-Crick manner, in that they only form base pairs with complimentary bases. <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref> However, the formation of Hydrogen bonds between the 3rd base on the codon and the 1st base on the anticodon can potentially occur in a non-Watson-Crick manner. Therefore different base pairs to those usually seen can form at this position.&nbsp;<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>&nbsp;  
  
 
==== Flexible Base Pairing at the 3rd Position of the “codon-anticodon duplex”&nbsp;<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>  ====
 
==== Flexible Base Pairing at the 3rd Position of the “codon-anticodon duplex”&nbsp;<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>  ====
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*If C is at the 3rd position in the codon it can base pair with G or I, if either of these is present at the 1st position in the anticodon.&nbsp;<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>
 
*If C is at the 3rd position in the codon it can base pair with G or I, if either of these is present at the 1st position in the anticodon.&nbsp;<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>
  
I is the nucleoside Inosine that is formed in tRNA by the removal of an amino group from adenosine <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>
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I is the nucleoside Inosine that is formed in tRNA by the removal of an amino group from adenosine <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>  
  
 
==== Reasons why more flexible base-pairing rules occur  ====
 
==== Reasons why more flexible base-pairing rules occur  ====
  
The 16S RNA in the 30S ribosomal subunit possesses a means of examining whether the standard Watson-Crick base pairs have formed between the 1st codon base and the 3rd anticodon base, as well as between the 2nd codon base and the 2nd anticodon base. However, there is no system to check whether the 3rd codon base and the 1st anticodon base are complimentary to one another and this amounts to the more lenient base-pairing that is witnessed exclusively at the 3rd position. <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>
+
The 16S RNA in the 30S ribosomal subunit possesses a means of examining whether the standard Watson-Crick base pairs have formed between the 1st codon base and the 3rd anticodon base, as well as between the 2nd codon base and the 2nd anticodon base. However, there is no system to check whether the 3rd codon base and the 1st anticodon base are complimentary to one another and this amounts to the more lenient base-pairing that is witnessed exclusively at the 3rd position. <ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>  
  
 
==== The consequent degeneracy of the Genetic Code  ====
 
==== The consequent degeneracy of the Genetic Code  ====
  
The Wobble Hypothesis explains why multiple codons can code for a single amino acid. One tRNA molecule (with one amino acid attached) can recognise and bind to more than one codon, due to the less-precise base pairs that can arise between the 3rd base of the codon and the base at the 1st position on the anticodon. This hence explains why more codons exist than there are specific tRNA molecules.&nbsp;<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>&nbsp;The Wobble Hypothesis also illustrates why the only variability between many codons, that encode the same amino acid, is their 3rd base (Alberts, p369).  
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The Wobble Hypothesis explains why multiple codons can code for a single amino acid. One tRNA molecule (with one amino acid attached) can recognise and bind to more than one codon, due to the less-precise base pairs that can arise between the 3rd base of the codon and the base at the 1st position on the anticodon. This hence explains why more codons exist than there are specific tRNA molecules.&nbsp;<ref>Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.</ref>&nbsp;The Wobble Hypothesis also illustrates why the only variability between many codons, that encode the same amino acid, is their 3rd base <ref>Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. (2008) Molecular Biology of The Cell, 5th edition, New York: Garland Science.</ref>
  
 
<references />
 
<references />

Revision as of 19:52, 3 January 2011

The Wobble Hypothesis, by Francis Crick, states that the 3rd base in an mRNA codon can undergo non-Watson-Crick base pairing with the 1st base of a tRNA anticodon [1] 

The mRNA codon’s first 2 bases form Hydrogen bonds with their corresponding bases on the tRNA anticodon in the usual Watson-Crick manner, in that they only form base pairs with complimentary bases. [2] However, the formation of Hydrogen bonds between the 3rd base on the codon and the 1st base on the anticodon can potentially occur in a non-Watson-Crick manner. Therefore different base pairs to those usually seen can form at this position. [3] 

Flexible Base Pairing at the 3rd Position of the “codon-anticodon duplex” [4]

I is the nucleoside Inosine that is formed in tRNA by the removal of an amino group from adenosine [6]

Reasons why more flexible base-pairing rules occur

The 16S RNA in the 30S ribosomal subunit possesses a means of examining whether the standard Watson-Crick base pairs have formed between the 1st codon base and the 3rd anticodon base, as well as between the 2nd codon base and the 2nd anticodon base. However, there is no system to check whether the 3rd codon base and the 1st anticodon base are complimentary to one another and this amounts to the more lenient base-pairing that is witnessed exclusively at the 3rd position. [7]

The consequent degeneracy of the Genetic Code

The Wobble Hypothesis explains why multiple codons can code for a single amino acid. One tRNA molecule (with one amino acid attached) can recognise and bind to more than one codon, due to the less-precise base pairs that can arise between the 3rd base of the codon and the base at the 1st position on the anticodon. This hence explains why more codons exist than there are specific tRNA molecules. [8] The Wobble Hypothesis also illustrates why the only variability between many codons, that encode the same amino acid, is their 3rd base [9]

  1. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. (2008) Molecular Biology of The Cell, 5th edition, New York: Garland Science.
  2. Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.
  3. Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.
  4. Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.
  5. Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.
  6. Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.
  7. Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.
  8. Berg J., Tymoczko J and Stryer L. (2007) Biochemistry, 6th edition, New York: WH Freeman.
  9. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. (2008) Molecular Biology of The Cell, 5th edition, New York: Garland Science.
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