Question

The nucleoside inosine frequently occurs as the third base in codons. What role does inosine play in wobble base pairing?

Short answer

Inosine allows tRNAs to bind to multiple codons, increasing efficiency and versatility in protein synthesis.

Step-by-step solution

Understanding Inosine in Codons

Inosine is a nucleoside that is commonly found in transfer RNA (tRNA) molecules. It often appears in the anticodon loop of tRNA at the position that pairs with the third base of the codon on mRNA.

Determine the Function of Wobble Base Pairing

Wobble base pairing is a feature of the genetic code that allows some tRNA molecules to pair with more than one mRNA codon. This is possible because the third position of the codon-anticodon pair does not always follow the standard Watson-Crick base pairing rules strictly.

Inosine's Role in Wobble Pairing

Inosine can pair with multiple different bases (adenine, cytosine, and uracil) at the third position of the mRNA codon. This flexibility allows a single tRNA to recognize and bind to different codons, thereby increasing the efficiency and flexibility of protein synthesis.

Conclusion

Inosine's ability to form non-standard base pairs with different nucleotides at the third codon position is crucial for the wobble hypothesis, making protein synthesis more efficient and versatile by reducing the number of tRNAs required.

Key concepts

tRNA

Transfer RNA (tRNA) is a crucial molecule involved in decoding messenger RNA (mRNA) into proteins. It acts as an adaptor that matches specific amino acids to corresponding codons on the mRNA. Each tRNA has an anticodon loop, which is a sequence of three nucleotides that can base pair with a complementary codon on the mRNA. The tRNA molecule carries an amino acid at the opposite end of the anticodon. When the tRNA anticodon pairs with the mRNA codon, the amino acid is added to the growing protein chain. This process occurs in the ribosome and is essential for translating the genetic code into functional proteins.

Codons

Codons are sequences of three nucleotides in mRNA that are read by the ribosome during protein synthesis. Each codon specifies a particular amino acid, or a stop signal, which tells the ribosome to stop translating the mRNA. Codons are key components of the genetic code. There are 64 different codons, but only 20 amino acids. This means that several codons can code for the same amino acid. For example, the codons UUU and UUC both code for the amino acid phenylalanine. This redundancy is known as the degeneracy of the genetic code.

Wobble Hypothesis

The wobble hypothesis is a concept developed by Francis Crick to explain how tRNA can recognize multiple codons for the same amino acid. According to this hypothesis, the first two bases of the codon-anticodon pair follow standard Watson-Crick base pairing rules (A-U and G-C), but the third base can 'wobble' and allow some flexibility. This means that certain tRNA molecules can bind to more than one codon. This significantly enhances the efficiency of protein synthesis, as fewer tRNA molecules are needed to decode the entire set of codons. For instance, Inosine in tRNA can pair with adenine, cytosine, and uracil, which allows a single tRNA to recognize multiple codons.

Non-Standard Base Pairing

Non-standard base pairing occurs when bases pair in ways that do not follow the traditional Watson-Crick base pairing rules. This is observed at the third position of the codon and is a key aspect of the wobble hypothesis. Inosine, a nucleoside found in tRNA, is a perfect example of this. Inosine can form hydrogen bonds with adenine, cytosine, and uracil. This non-standard pairing capability makes the genetic code more versatile and increases the adaptability of the organism. It allows cells to use fewer tRNA molecules, making protein synthesis more economical and efficient.