Problem 69 - Chemistry A Molecular Approach

Question

A monomeric protein contains 154 amino acids. How many codons code for these amino acids? How many nucleotides? MISSED THIS? Read Sections 23.6,23.7

Step-by-Step Solution

Answer

154 codons, 462 nucleotides.

Step 1: Understanding Codon to Amino Acid Relationship

Recall from the genetic code that each amino acid in a protein is coded by a sequence of three nucleotides, known as a codon. Therefore, each amino acid is represented by one codon.

Step 2: Calculating the Number of Codons

Since there is a one-to-one correspondence between an amino acid and a codon, if there are 154 amino acids, there will be 154 codons.

Step 3: Calculating the Number of Nucleotides

As each codon consists of three nucleotides, to find the total number of nucleotides, multiply the number of codons (154) by 3.

Key Concepts

Codon to Amino Acid Relationship

Understanding the genetic code is essential for grasping how proteins are synthesized in living organisms. Each amino acid, the building block of proteins, is specified by a unique sequence of three nucleotides termed a codon. This triplet code is universal and is the foundation for protein synthesis during the process of translation within a cell.

For instance, the codon AUG not only serves as a start signal for translation but also codes for the amino acid methionine. Similarly, there are codons such as UUU and UUC that both code for the amino acid phenylalanine. This redundancy in the genetic code, known as degeneracy, means that multiple codons can correspond to a single amino acid, providing a buffer against mutations that might otherwise have detrimental effects if the genetic code were more rigid.

Calculating the Number of Codons

With a basic grasp of the relationship between codons and amino acids, calculating the number of codons needed to encode a protein becomes straightforward. Given that each codon corresponds to a single amino acid, we can determine the number of codons in a protein by simply counting its amino acids.

In the context of the exercise, for a protein comprising 154 amino acids, an equivalent number of 154 codons are required to encode it. This direct correlation allows researchers and students alike to easily determine the length of the messenger RNA (mRNA) sequence necessary for the synthesis of a given protein.

Nucleotide Composition in Proteins

Transitioning from the number of codons to the number of nucleotides in a protein is a matter of simple multiplication because there are always three nucleotides per codon. For a protein encoded by 154 codons, as per the information provided in the exercise, the number of nucleotides would be \(154 \times 3 = 462\) nucleotides. This calculation provides a clearer picture of the actual genetic footprint required to produce a specific protein and is important for deeper molecular biology studies, such as DNA sequencing and genetic engineering, where precise nucleotide sequence information is crucial.