Problem 21 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

A sequence of how many nucleotides in messenger RNA makes a codon for an amino acid? |CBSE 2004] (a) Three (b) Four (c) One (d) Two

Step-by-Step Solution

Answer

Three nucleotides make a codon in mRNA.

Step 1: Understanding the Question

The question asks about the number of nucleotides in messenger RNA (mRNA) that make up a codon, which then codes for a single amino acid. Codons are part of the genetic code used in the process of translation.

Step 2: Recall the Genetic Code

In biology, the genetic code is composed of sequences of nucleotides in mRNA, where each set of three nucleotides forms a codon. This codon specifies one amino acid or a stop signal during protein synthesis.

Step 3: Recognize Codon Structure

A single codon is a sequence of three nucleotides in mRNA. Therefore, each codon is responsible for coding one specific amino acid in a protein.

Step 4: Conclusion and Answer Selection

Given the knowledge that a codon is made up of three nucleotides, we conclude that option (a) Three is the correct answer.

Key Concepts

Codons

Codons are fundamental units of the genetic code, found within messenger RNA (mRNA). They are triplets of nucleotides that provide the instructions for building proteins. Each codon corresponds to a particular amino acid or a stop signal in the protein synthesis process.

Here’s more on how this works:

• Each codon consists of exactly three nucleotides. This triplet formation is critical because it ensures the genetic message is read in the correct sequence.
• With four different nucleotides in RNA – adenine (A), cytosine (C), guanine (G), and uracil (U) – there are 64 possible codon combinations. This allows for the coding of 20 standard amino acids, with some redundancy, meaning multiple codons can specify the same amino acid.
• Codons are universal in almost all organisms, emphasizing their importance in biology. They connect the genotype carried by the nucleotides to the phenotype expressed in proteins.

Understanding codons is vital, as alterations in their sequence can lead to changes in protein structure and function, potentially causing genetic disorders or traits.

Messenger RNA (mRNA)

Messenger RNA (mRNA) serves as the crucial intermediary between DNA and proteins in the process of gene expression. It is a type of RNA that carries genetic information from the DNA in the nucleus to the ribosomes, where protein synthesis occurs.

Let’s delve into its role:

• Transcription is the first phase where mRNA is synthesized based on the DNA template. This involves unwinding the DNA double helix and using one strand as a guide to form the mRNA sequence.
• mRNA is a single-stranded molecule, enabling it to pass out of the nucleus into the cytoplasm where ribosomes, the protein factories, reside.
• In translation, the sequence of nucleotides in mRNA is read in sets of three – the codons. Each codon calls for a specific amino acid to be added to the growing protein chain.

mRNA is essential for dictating the amino acid sequence of the resulting protein, thus directly influencing each protein's structure and function within a cell.

Protein Synthesis

Protein synthesis is the process by which cells build proteins based on genetic instructions carried by mRNA. It occurs in two main stages: transcription and translation, and it’s indispensable for cellular function and organism growth.

Here’s how the process unfolds:

• Transcription: This is the first stage, where DNA is transcribed to form mRNA in the cell nucleus. The mRNA serves as a portable copy of the genetic instructions. Once transcription is complete, the mRNA exits the nucleus.
• Translation: Taking place in the ribosome, translation reads the sequences of codons in mRNA to produce a polypeptide chain. Transfer RNA (tRNA) molecules bring the corresponding amino acids to the ribosome, matching their anticodons to the mRNA codons, ensuring accuracy in protein building.
• As amino acids link together, they fold to form a functional protein. This folding is crucial for the protein's activity and is dictated by the sequence and chemical characteristics of the constituent amino acids.

Protein synthesis is essential as proteins serve countless roles throughout the body, from structural elements, enzymes, and antibodies, to signals and receptors. Each protein's unique structure allows it to perform its specific function within the organism.