Problem 87 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following statements is true for protein synthesis (translation)? (a) amino acids are directly recognized by \(\mathrm{m}\)-RNA (b) the third base of the codon is less specific (c) only one codon codes for an amino acid (d) every t-RNA molecule has more than one amino acid attachment.

Step-by-Step Solution

Answer

Option (b) is true: the third base of the codon is less specific.

Step 1: Understanding the Question

The question asks which statement is true regarding the process of protein synthesis, specifically the translation phase. We need to evaluate each option and determine its accuracy based on the principles of molecular biology.

Step 2: Evaluating Option A

Option (a) states that amino acids are directly recognized by mRNA. This is incorrect because it is tRNA, not mRNA, that brings the amino acids to the ribosome and matches them with the codons on the mRNA.

Step 3: Evaluating Option B

Option (b) suggests that the third base of the codon is less specific. This is true due to a phenomenon known as the 'wobble hypothesis,' where the third base of the codon can often vary without affecting the amino acid it codes for.

Step 4: Evaluating Option C

Option (c) states that only one codon codes for an amino acid. This is false. Most amino acids are actually coded by more than one codon, which is referred to as degeneracy of the genetic code.

Step 5: Evaluating Option D

Option (d) claims that every tRNA molecule has more than one amino acid attachment. This is incorrect because each tRNA molecule is specific to one amino acid, having only one attachment site for it.

Step 6: Conclusion

Based on the analysis, option (b) is the true statement, as the third base of many codons can indeed vary without changing the amino acid they encode, due to the wobble effect.

Key Concepts

Translation Process

Protein synthesis is a vital process through which cells create proteins. It consists of two main phases: transcription and translation. During transcription, DNA is converted into messenger RNA (mRNA), which then carries genetic information to the ribosome. Translation is the next phase and involves converting the mRNA sequence into a chain of amino acids, eventually folding into a functional protein.

• The ribosome, a complex molecular machine, reads the sequence of the mRNA.
• Transfer RNA (tRNA) molecules bring the appropriate amino acids to the ribosome.
• Amino acids are linked together by peptide bonds, forming a polypeptide chain.

This process is highly coordinated and essential for maintaining the cell's functions. It involves various molecules, each with a specific role, ensuring proteins are synthesized accurately and efficiently.

Wobble Hypothesis

The wobble hypothesis is an interesting aspect of genetic coding proposed by Francis Crick. It explains why multiple codons can code for the same amino acid. The genetic code consists of codon triplets, and while the first two bases are usually very specific, the third base can "wobble"—meaning it can tolerate some variability.

• This flexibility allows a tRNA to recognize multiple codons.
• The phenomenon contributes to genetic code degeneracy, where several codons may correspond to a single amino acid.

This hypothesis is fundamental in understanding how proteins can be synthesized efficiently even if minor errors occur in the coding sequence. This flexibility helps in combating minor mutations or errors, ensuring that protein function is usually maintained.

tRNA Function

Transfer RNA, or tRNA, plays a crucial role in the translation process by acting as the adapter molecule that connects mRNA codons to the corresponding amino acids. Each tRNA has a three-nucleotide sequence known as the anticodon, which pairs with the codon in mRNA.

• Each tRNA is specific to one amino acid and carries it to the ribosome.
• The anticodon ensures that the correct amino acid is added to the growing polypeptide chain.
• The aminoacyl-tRNA synthetases are enzymes that charge the tRNA with its specific amino acid.

This system is essential for accurate protein synthesis, as it ensures that the genetic code is translated correctly. Without tRNA, the ribosome would not be able to match amino acids with the mRNA codons, leading to errors in protein construction.

Codon Specificity

Codon specificity refers to the precise matching of mRNA codons with their respective amino acids. Each mRNA codon consists of three nucleotides and matches with an anticodon on a tRNA molecule that brings a specific amino acid to the ribosome.

• The genetic code is described as degenerate because several codons can encode the same amino acid.
• Despite this degeneracy, each codon specifies exactly one amino acid, maintaining precise protein coding.
• Exceptions can occur, such as the "wobble" base pairing, which still ensures fidelity in protein synthesis.

Codon specificity is a cornerstone of genetic coding, ensuring that proteins are built correctly, performing their intended functions effectively within the cell organizations. Understanding this helps unravel the accuracy and complexity of biological systems.