Explain how the \"wobble\" position of any anticodon can engage in non-Watson-Cr
ID: 3521209 • Letter: E
Question
Explain how the "wobble" position of any anticodon can engage in non-Watson-Crick nucleotide pairing with the codon, while the other two positions follow W-C pairing rules. Be as chemically explicit as possible.
Problem #4 (25 points). On the (W-C) base-pairing surface of a nucleotide, the three key locations for H-bond donating and accepting can be viewed as three boxes from the “top” to the “bottom” in the way that nucleobases are typically drawn. The “top” box is determined by the 6-position in purines and the 4-position in pyrimidines. The "middle" box is determined by the 1-position in purines and the 3-position in pyrimidines. The "bottom" box is determined by the 2-position in both purines and pyrimidines. Imagine the cell needs to code for a valine aminoacyl- tRNA synthetase (ValRS) enzyme. This is a class I synthetase, and consequently has two conserved amino-acid blocks, one of which is five amino acids long. Now, consider a possible mRNA sequence needed to decode this peptide using the standard genetic code. Write such a sequence and then fill in the following boxes with a D, an A, or an X at physiological temperature and pH: 5 top middle bottom What is the physical length of this mRNA in A), assuming it is in a standard A-form helix (complexed perhaps with the template DNA strand from which it is being transcribed)? How many atoms are in the phosphate backbone of this mRNA molecule? What is the information content in your answer in the Table above?Explanation / Answer
DNA double helix model as proposed by Watson, Crick and Wilkins consists of four base pairs namely- adenine , guanine, cytosine and thymine. The four base pairs follow a fixed pattern of their pairing as proposed by them. Adenine always base pairs with thymine via two hydrogen bonds while guanine base pairs with cytosine by three hydrogen bonds,.
DNA follows the central dogma which states that DNA would copy itself; process called replication; then changes to RNA; process called transcription , and later changes to proteins; process called translation.
DNA-RNA-Proteins.
For protein synthesis to occur, the requirements are the genetic codon ( which are the segments of three base pairs on the mRNA molecule), t RNA molecule which bears an anticodon loop complementary to the codons on mRNA coding for a particular amino acid.
Since there are a total of sixty four codons among which sixty one are coding and the remaining three are called as non sense or the stop codons; it was proposed that a total of sixty one tRNAs would be present in the cell bearing a specific anticodon for their respective codons on the mRNA molecule.
However later Francis crick proposed the wobble concept. The concept states that the base present at the 5’ end of the anticodon shows a non specific and non standard base pairing with many of the bases present in the 3’ end of the codon. That is it does not follow the standard base pairing methods.
Hence first base of the anticodon and third base of the codon are said to in the wobble position to each other and this also suggests that the total number of tRNA molecules available for the protein synthesis need not be sixty one.
Given below are the pairing combinations with the wobble concept as proposed by Crick
Base in anticodon Base in codon
A U
G U, C
C G
U A, G
I A, U, C
Where A= adenine
U=uracil
G=guaine
C=cytosine
I=inosine
mRNA= messenger RNA
tRNA= transfer RNA
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