Question

Codons in the set CUU, CUC, CUA, and CUG all code for the amino acid leucine. In this set, the first and second bases are identical; the identity of the third base is irrelevant. For what other sets of codons is the third base also irrelevant? For what amino acid(s) does each set code?

Short answer

Question: Identify sets of codons where the third base is irrelevant to determine the amino acid they code for, just like the given set of codons (CUU, CUC, CUA, and CUG) that code for leucine. List the corresponding amino acids as well. Answer: The sets of codons with an irrelevant third base are: a. UUU, UUC b. UUA, UUG, CUU, CUC, CUA, CUG c. AUU, AUC, AUA d. GUU, GUC, GUA, GUG These sets code for the following amino acids: a. Phenylalanine b. Leucine c. Isoleucine d. Valine

Step-by-step solution

Understand the genetic code

Genetic code is a set of rules used by living cells to translate information encoded within genetic material (DNA or mRNA sequences of nucleotide triplets, or codons) into proteins. Amino acids are coded by a group of 3 bases called codons. We will find the sets of codons where the third base does not determine the amino acid.

Identify the sets where the third base is irrelevant

We start by identifying all sets of codons that code for the same amino acid irrespective of the third base identity, just like how all CUU, CUC, CUA, and CUG code for leucine. Possible sets are: 1. UUU, UUC (Phenylalanine) 2. UUA, UUG, CUU, CUC, CUA, CUG (Leucine) 3. AUU, AUC, AUA (Isoleucine) 4. GUU, GUC, GUA, GUG (Valine)

Identify the amino acids for each set

By examining the genetic code table, we can determine the corresponding amino acids for each set. 1. Phenylalanine: UUU, UUC 2. Leucine: UUA, UUG, CUU, CUC, CUA, CUG (Already given) 3. Isoleucine: AUU, AUC, AUA 4. Valine: GUU, GUC, GUA, GUG So, the answer is: 1. The sets of codons are: a. UUU, UUC b. UUA, UUG, CUU, CUC, CUA, CUG c. AUU, AUC, AUA d. GUU, GUC, GUA, GUG 2. These sets code for the following amino acids: a. Phenylalanine b. Leucine c. Isoleucine d. Valine

Key concepts

Codons

Codons are the basic units of the genetic code, often likened to the 'words' that spell out the instructions for making proteins. These units consist of three nucleotides in a row within an RNA sequence. Each codon corresponds to a specific amino acid, the building block of a protein, or signals the start and stop of protein synthesis. The beauty of the genetic code lies in its redundancy; for instance, in your exercise, CUU, CUC, CUA, and CUG all specify the same amino acid, leucine.

As understanding the role of codons is critical for genetics, it's instructive to note that certain codons can vary in their third nucleotide yet still code for the same amino acid. This phenomenon, known as 'wobble', allows for a level of tolerance to mutations that may occur within the genetic sequence.

Amino Acids

Amino acids are organic compounds that combine to form proteins, which are crucial to the functioning of all living cells. There are twenty standard amino acids, each with a unique side chain, making them distinct. The genetic code defines how sequences of codons are translated into a string of amino acids to build a protein. In the exercise, for example, amino acids like leucine, phenylalanine, isoleucine, and valine are encoded by multiple codons.

The relationship between codons and amino acids is not one-to-one; several codons can lead to the same amino acid. This aspect of the genetic code is key for its fault tolerance, as a mutation in the DNA that alters only the third base of a codon may not change the resulting amino acid, and therefore may not affect the protein function.

Nucleotide Triplets

Nucleotides are the building blocks of nucleic acids like DNA and RNA, and they are composed of a sugar, a phosphate group, and a nitrogenous base. When we refer to nucleotide triplets, we are talking about groups of three nucleotides that together form a codon. To illustrate, a triplet could be ACG, where 'A' stands for adenine, 'C' for cytosine, and 'G' for guanine.

These triplets are crucial because they dictate the type of amino acid that will be incorporated into a growing protein chain during the process of protein synthesis. Mutations, or changes in these nucleotide sequences, can lead to changes in the protein structure and function, with potential impacts on an organism's health or characteristics.

Protein Synthesis

Protein synthesis is the process by which cells build proteins based on the instructions given by the genetic code. This complex process involves two main stages: transcription and translation. During transcription, the information encoded in the DNA is transferred to messenger RNA (mRNA). Translation follows, where the mRNA works with ribosomes and transfer RNA (tRNA) to 'read' the nucleotide triplets, or codons, and assemble the corresponding amino acids into a protein.

Each step of protein synthesis is fine-tuned to ensure that the correct sequence of amino acids is constructed. The redundancy in the genetic code is an essential feature that contributes to the accuracy and efficiency of this process, as seen with codons in the exercise, where changes in the third base do not alter the designated amino acid.