Protein translation proceeds as an ordered process and involves all of the following steps EXCEPT

Options

A. ribosomes reads the mRNA in the 5' to 3' direction
B. peptide synthesis proceeds from the amino-terminus to the carboxyl-terminus
C. if present within the coding region, AUG represents valine and GUG represents methionine
D. chain elongation requires the activity of multiple tRNA molecules

Answer

To solve the question regarding the steps involved in protein translation, we will analyze each of the provided options and determine which one does not belong to the process of translation.

### Step-by-Step Solution:

1. **Understand the Process of Translation**:
Translation is the process by which ribosomes synthesize proteins based on the sequence of codons in mRNA. It involves several key steps: initiation, elongation, and termination.

2. **Evaluate Each Statement**:
- **Statement 1**: "Ribosome reads the mRNA from 5' to 3' direction."
- This statement is correct. Ribosomes indeed read the mRNA in the 5' to 3' direction during translation.

- **Statement 2**: "Peptide synthesis proceeds from amino acid terminus to the carboxyl terminus."
- This statement is also correct. During protein synthesis, the peptide chain grows from the amino (N) terminus to the carboxyl (C) terminus.

- **Statement 3**: "If present within the coding region, AUG represents valine whereas GUG represents methionine."
- This statement is incorrect. AUG is the start codon and codes for methionine, not valine. GUG can code for valine but not in the context of being a start codon.

- **Statement 4**: "Elongation requires the activity of multiple tRNA molecules."
- This statement is correct. During the elongation phase, various tRNA molecules bring specific amino acids to the ribosome according to the codon sequence on the mRNA.

3. **Identify the Incorrect Statement**:
- From the analysis, Statement 3 is the only one that does not accurately describe a step in the protein translation process. Therefore, it is the answer to the question.

### Final Answer:
The statement that is NOT a part of the protein translation process is: **"If present within the coding region, AUG represents valine whereas GUG represents methionine."**

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