The Question is from neet-botany molecular-basis-of-inheritance , and it was created by the author Mr. NARESH KUMAR K

Question

A researcher is studying translation in a prokaryotic cell.  They introduce a modified mRNA where all the guanine nucleotides in the coding sequence are replaced with inosine. Which of the following is the MOST LIKELY effect on translation?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
 **Primary Concept**: Translation and codon-anticodon interaction
 **Related Topics**: Genetic code, mRNA modification, wobble hypothesis
 **Prerequisites**: Understanding of the process of translation, the genetic code, and the structure of tRNA.
## SOLUTION PATHWAY
**Given Information**:
  mRNA with all guanines replaced by inosine.
  Prokaryotic cell.
**Method & Steps**:
 1. Understand the role of guanine in codons.
  Reasoning: Guanine is one of the four nitrogenous bases (A, U, G, C) that make up mRNA codons.  Each codon specifies a particular amino acid during translation.
 2. Consider the properties of inosine.
  Working: Inosine (I) is a nucleoside that can base-pair with U, C, and A.  This means that replacing G with I can alter codon specificity.
  Key Point: The wobble hypothesis explains that the third base in a codon can sometimes have non-standard base pairing with the anticodon.  Inosine's ability to base-pair with multiple bases is a key example of this.
 3. Predict the effect on translation.
  Result: Since inosine can pair with different bases, replacing guanine with inosine will change the meaning of some codons, leading to the incorporation of different amino acids into the polypeptide chain.  This results in an altered protein sequence.
  Verification: The wobble hypothesis supports the idea that changing a base, particularly at the third position, can lead to a different amino acid being incorporated, but not necessarily a premature stop codon.  The ribosome is unlikely to be unable to bind the modified mRNA, as the overall structure is still largely intact.
 ## OPTION ANALYSIS
A :x: Inosine does not act as a stop codon.
B :x: The ribosome binding site (usually upstream of the coding sequence) is unlikely to be significantly affected by changes within the coding sequence.
C :x: Replacing G with I changes the codons, so the protein will not be identical.
D ✓: The altered codons due to the substitution of inosine for guanine will result in a different amino acid sequence in the synthesized protein. 
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Assuming inosine will always cause premature termination: Inosine can pair with multiple bases, leading to amino acid substitutions, not necessarily termination.
  2.Ignoring the wobble hypothesis: The flexibility in base pairing at the third codon position is crucial in understanding the effect of inosine.
 **Quick Tips**:
  1.Remember the wobble hypothesis and the non-standard base pairing possibilities.
  2.Consider the potential changes to codon meaning when a base is replaced.

Mr. NARESH KUMAR K · Answer

Translation will terminate prematurely due to the presence of inosine.

Mr. NARESH KUMAR K · Answer

The ribosome will be unable to bind to the modified mRNA.

Mr. NARESH KUMAR K · Answer

The protein synthesized will be identical to the one produced from the unmodified mRNA.

Mr. NARESH KUMAR K · Answer

The correct Option is "The protein synthesized will have altered amino acid sequence due to changes in codon recognition."

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