Question

The \(\alpha\) chain of eukaryotic hemoglobin is composed of 141 amino acids. What is the minimum number of nucleotides in an mRNA coding for this polypeptide chain?

Short answer

Answer: The minimum number of nucleotides in an mRNA coding sequence for a polypeptide chain with 141 amino acids is 423.

Step-by-step solution

Understanding the components of a polypeptide chain and mRNA

A polypeptide chain is composed of amino acids, which are encoded by nucleotide triplets called codons on the mRNA molecule. In general, one codon is made up of three nucleotides, and each codon codes for one specific amino acid.

Calculate the number of codons required for encoding 141 amino acids

Since one codon encodes one amino acid, the number of codons required for encoding a polypeptide chain of 141 amino acids will also be 141.

Calculate the minimum number of nucleotides required for encoding 141 codons

To determine the minimum number of nucleotides required for encoding 141 codons, we simply multiply the number of codons by the number of nucleotides in each codon (which is 3). So, the minimum number of nucleotides will be: Minimum number of nucleotides = Number of codons × Number of nucleotides per codon Minimum number of nucleotides = 141 × 3 Minimum number of nucleotides = 423 Therefore, the minimum number of nucleotides in an mRNA coding for this polypeptide chain is 423.

Key concepts

Codon and Amino Acid Relationship

The language of life lies in the way cells translate genetic information into functional proteins. At the heart of this biological conversation is the relationship between codons and amino acids. A codon consists of three nucleotide bases in messenger RNA (mRNA). These nucleotides are the smallest units of the genetic code, coming in four types: adenine (A), uracil (U), cytosine (C), and guanine (G). The sequence of these bases determines which amino acid will be added next in the growing polypeptide chain during protein synthesis.

There are 64 different possible codons, but only 20 standard amino acids, which means there's a redundancy in the genetic code, known as its 'degeneracy'. This implies multiple codons can encode for the same amino acid. For example, the codons UUU and UUC both code for the amino acid phenylalanine. This aspect of the relationship is crucial as it provides a buffer against some mutations allowing organisms to maintain proper function even with minor genetic variations.

Nucleotide Triplets

Nucleotide triplets are the consecutive sequences of three nucleotides on an mRNA strand that constitute a codon. Their role is essential in determining the structure and function of proteins. Each triplet is read in a non-overlapping, linear fashion during the translation process. The nature of this triplet code is universal across almost all living organisms, illustrating the shared heritage of life on Earth.

Furthermore, since the genetic code is redundant but not ambiguous, each triplet distinctly codes for a single amino acid or a stop signal—but never more than one. This precision ensures that during translation, the correct amino acids are added sequentially to elongate the polypeptide chain, thereby 'spelling' out the exact protein necessary for a particular function in an organism.

Protein Synthesis

Protein synthesis is an essential biological process that translates the genetic blueprint into the workhorses of the cell—proteins. This intricate process occurs in two primary stages: transcription and translation. During transcription, DNA's double helix unwinds, and one strand serves as a template for creating a complementary mRNA strand. Once the mRNA is transcribed, it leaves the nucleus and travels to a ribosome, the 'protein factory' of the cell.

Translation is where the real construction of the protein happens. The mRNA, equipped with codons, is read by the ribosome, and transfer RNA (tRNA) molecules bring the correct amino acids to create the polypeptide chain. Each amino acid is added to the growing chain in the sequence dictated by the nucleotide triplets on the mRNA, and the process repeats until the ribosome encounters a stop codon, signalling the end of the protein synthesis. The resulting polypeptide chain then folds into its unique three-dimensional structure to become a functional protein, ready to perform its role in the cell.