Question

REFLECT AND APPLY It is possible for the codons for a single amino acid to have the first two bases in common and to differ in the third base. Why is this experimental observation consistent with the concept of wobble?

Short answer

It is consistent because wobble allows variations in the third base without changing the amino acid coded.

Step-by-step solution

Understand Codons and Amino Acids

Codons are sequences of three nucleotide bases in mRNA that specify particular amino acids. Multiple codons can code for the same amino acid, a concept known as codon redundancy.

Define the Concept of Wobble

The wobble hypothesis states that the third base in a codon can 'wobble' or vary without changing the amino acid it codes for. This allows for some flexibility or variability at the third position of the codon.

Connect Experimental Observations to Wobble

Given the data that codons for a single amino acid have the first two bases in common but differ in the third, this aligns with the wobble hypothesis. This is because the first two bases are critical for coding the amino acid, while variations in the third base still result in the same amino acid due to wobble.

Conclude the Reasoning

The observation that codons for a single amino acid share the first two bases and vary in the third aligns with the wobble hypothesis, as it explains how variations at the third base position can still result in the same amino acid.

Key concepts

Codons

Codons are the fundamental units of the genetic code. Each codon is a sequence of three nucleotide bases in messenger RNA (mRNA). These sequences are critical in the process of translating genetic information into proteins.

There are 64 possible codons in the genetic code, each of which corresponds to a specific amino acid or a stop signal during protein synthesis. For example, the codon AUG serves as the start codon and also codes for the amino acid methionine.

Multiple codons can code for the same amino acid, and this phenomenon is known as codon redundancy. This redundancy plays a crucial role in protecting the organism against errors in protein synthesis. If a mutation occurs in one base of a codon, it might still result in the same amino acid due to redundancy.

Amino Acids

Amino acids are the building blocks of proteins. Each protein is made up of one or more chains of amino acids. There are 20 different amino acids commonly found in the proteins of living organisms.

The sequence and number of amino acids determine the structure and function of a protein. This sequence is directly dictated by the sequence of codons in the mRNA. Each amino acid is encoded by one or more specific codons.

For instance, the amino acid leucine can be encoded by the codons UUA, UUG, CUU, CUC, CUA, and CUG. This exemplifies codon redundancy, where different codons can specify the same amino acid.

mRNA

mRNA, or messenger RNA, acts as a template for protein synthesis. It carries the genetic information transcribed from DNA to the ribosome, where proteins are synthesized.

The mRNA sequence is read in sets of three nucleotide bases, known as codons. Each codon specifies a particular amino acid, which will be added to the growing polypeptide chain during translation.

For example, if the mRNA sequence is AUG CGA UUA, the corresponding amino acids would be methionine (start), arginine, and leucine. The ribosome reads the mRNA codons in the 5' to 3' direction, ensuring that the genetic code is accurately translated into a functional protein.

Codon Redundancy

Codon redundancy, also known as degeneracy of the genetic code, refers to the fact that multiple codons can encode the same amino acid. This feature is essential for the robustness of protein synthesis.

For example, the amino acid serine is encoded by the codons UCU, UCC, UCA, UCG, AGU, and AGC. This repetition in coding provides a safeguard against mutations, ensuring that a single base change unlikely alters the amino acid sequence of the protein.

The wobble hypothesis helps explain codon redundancy. According to this theory, the third base in a codon can often vary without changing the specified amino acid. This flexibility in the third codon position allows for a 'wobble,' facilitating accurate and efficient protein synthesis even in the presence of certain mutations.