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, and the identity of the third base is irrelevant. For what other sets of codons is the third base also irrelevant, and for what amino \(\operatorname{acid}(\mathrm{s})\) does each set code?

Short answer

Question: Identify other sets of codons where the third base is irrelevant, and determine which amino acid each set codes for. Answer: The sets of codons with irrelevant third bases and their corresponding amino acids are: 1. Valine (Val) - GUU, GUC, GUA, and GUG. 2. Phenylalanine (Phe) - UUU, UUC. 3. Leucine (Leu) - UUA, UUG, CUU, CUC, CUA, and CUG. 4. Proline (Pro) - CCU, CCC, CCA, and CCG. 5. Threonine (Thr) - ACU, ACC, ACA, and ACG. 6. Alanine (Ala) - GCU, GCC, GCA, and GCG.

Step-by-step solution

Identify the Genetic Code Table

To find sets of codons where the third base is irrelevant, you need to use a genetic code table, which shows the 64 possible codon combinations and their corresponding amino acids.

Look for Sets with Similarities in the First and Second Bases

In the given example, CUU, CUC, CUA, and CUG all code for leucine. Notice that the first two bases are the same (CU) and only the third base is different. Look for other sets of codons in the genetic code table with identical first and second bases, and where the third base doesn't affect the corresponding amino acid.

Identify Sets With Irrelevant Third Bases

After examining the table, you will find the following sets of codons that meet the criteria: 1. GUU, GUC, GUA, and GUG all code for valine (Val). 2. UUU, UUC code for phenylalanine (Phe). 3. UUA, UUG, CUU, CUC, CUA, and CUG all code for leucine (Leu). 4. CCU, CCC, CCA, and CCG all code for proline (Pro). 5. ACU, ACC, ACA, and ACG all code for threonine (Thr). 6. GCU, GCC, GCA, and GCG all code for alanine (Ala). In each set, the first and second bases are the same, and the identity of the third base is irrelevant to determining the amino acid.

Listing the Amino Acids and Sets

Now that we have identified the sets of codons with irrelevant third bases, we can list them along with their corresponding amino acids: 1. Valine (Val) - GUU, GUC, GUA, and GUG. 2. Phenylalanine (Phe) - UUU, UUC. 3. Leucine (Leu) - UUA, UUG, CUU, CUC, CUA, and CUG. 4. Proline (Pro) - CCU, CCC, CCA, and CCG. 5. Threonine (Thr) - ACU, ACC, ACA, and ACG. 6. Alanine (Ala) - GCU, GCC, GCA, and GCG. These are the sets of codons where the third base is irrelevant and their respective amino acids.

Key concepts

Codons

Codons are the building blocks of genetic codes. They are sequences of three nucleotides found in messenger RNA (mRNA) that specify which amino acids will be added to a growing polypeptide chain during protein synthesis. A set of three nucleotides is always needed for coding because, with this triplet arrangement, you can form 64 different combinations (4 bases at each position, giving 4 × 4 × 4 = 64 possible combinations).
Codons are vital because they serve as the key to translating the genetic information stored in DNA into functional proteins. Every group of three RNA bases codes for an amino acid or a signal to stop or start protein synthesis. Thus, understanding codons is crucial for comprehending how genetic information is read and utilized at a cellular level.

Amino Acids

Amino acids are the fundamental components of proteins, which are crucial molecules in every living organism. There are 20 different amino acids that can appear in proteins, and each one is uniquely encoded by specific codons.
When the genetic code is translated, each codon provides the instructions to add a particular amino acid to a protein chain. Thus, a sequence of codons will determine the sequence of amino acids, ultimately defining the protein's structure and function. For example, the codons UUU and UUC both code for the amino acid phenylalanine, illustrating how different codons can specify the same amino acid.
Proteins, made up of long chains of amino acids, are involved in almost every cellular process, ranging from structural roles to catalyzing biochemical reactions. Therefore, amino acids and their codons are central to the function and maintenance of life.

Third Base Redundancy

Third base redundancy is a fascinating feature of the genetic code where changes in the third nucleotide of a codon may still produce the same amino acid. This is due to the wobble hypothesis, which suggests flexibility at the third position in the pairing between codon and anticodon during translation.
For instance, the codons CUU, CUC, CUA, and CUG all code for the same amino acid, leucine, despite having different third bases. This redundancy serves as a protective mechanism. It reduces the effects of mutations since changes in the third base do not always alter the amino acid sequence. This ensures that proteins can be synthesized correctly even if some mutations occur. Understanding this redundancy helps explain why the genetic code is considered "degenerate," meaning there is more than one codon for most amino acids in the code.

Genetic Code Table

The genetic code table is an essential tool for anyone studying molecular biology. It organizes the 64 possible codon combinations and indicates which of the 20 amino acids or stop signals each codon correlates with. The table is usually arranged to show codons grouped by their first two bases, which helps identify patterns, such as third base redundancy.
Using this table, one can easily decipher the mRNA sequence into an amino acid sequence, understanding exactly how genetic information translates into proteins. It highlights the codons, like GUU, GUC, GUA, and GUG, which all code for valine, regardless of the third base, and identifies stop codons which signal the end of protein synthesis.
The table thus acts as a decoder, connecting the language of nucleic acids to the language of proteins, and is crucial for interpreting genetic data and mutations accurately.