Problem 52 - A Complete Resource Book in Chemistry for JEE Main

Question

A sequence of how many nucleotides in messenger RNA makes a codon for an amino acid? (a) one (b) two (c) three (d) four

Step-by-Step Solution

Answer

The sequence of three nucleotides in mRNA makes a codon for an amino acid. (c) three.

Step 1: Understand the Sequence in mRNA

In messenger RNA (mRNA), nucleotides are the building blocks that code for amino acids. A particular set of nucleotides forms what is known as a 'codon'.

Step 2: Codons and Their Role

A codon is a sequence of nucleotides that pairs with transfer RNA to add a specific amino acid to a growing protein chain. Each codon corresponds to one amino acid.

Step 3: Determine the Length of a Codon

In the genetic code, each codon is made up of three nucleotides. This sequence dictates which amino acid will be added during protein synthesis.

Step 4: Answer the Question

Based on the information above, the sequence of three nucleotides in mRNA makes a codon for an amino acid. Thus, the correct answer is (c) three.

Key Concepts

Nucleotide Sequence

To grasp the concept of DNA and RNA, it's important to first understand nucleotide sequences. Nucleotides are the basic building blocks of nucleic acids like DNA and RNA. Each nucleotide is composed of a sugar, a phosphate group, and a nitrogenous base.
Nucleotide sequences are specific arrangements of these nucleotides that carry genetic information. In DNA, the sequence of nucleotides determines everything about an organism – from its genetic traits to its cellular functions. RNA sequences, particularly those in messenger RNA (mRNA), are crucial for protein synthesis.

• DNA contains the bases adenine (A), cytosine (C), guanine (G), and thymine (T).
• In RNA, thymine is replaced by uracil (U).
• The order of these bases in an mRNA strand dictates the process of creating proteins in cells.

Codon

A codon is a specific sequence of three nucleotides in mRNA. Each codon corresponds to a specific amino acid or a signaling function during the protein synthesis.

• mRNA is read in sets of three nucleotides at a time, known as a codon.
• Each codon specifies either an amino acid or a stop signal during protein synthesis.
• For example, the codon AUG not only codes for the amino acid methionine but also serves as a start signal for protein synthesis.

Understanding codons is crucial because they dictate the exact order in which amino acids are introduced into a protein. This, in turn, determines the protein's structure and function.

Protein Synthesis

Protein synthesis is a vital biological process where cells build proteins. It occurs in two main stages: transcription and translation. **Transcription** During transcription, a particular segment of DNA is copied into RNA, specifically mRNA. This mRNA then serves as a template to guide the construction of proteins.
**Translation** Once transcription is complete, the mRNA moves to the ribosome, the protein-making machinery of the cell. Here, the mRNA's nucleotide sequence is read and translated into a sequence of amino acids, which are the building blocks of proteins.

• tRNA (transfer RNA) plays a key role during translation by bringing the appropriate amino acid to the ribosome as it reads each codon of the mRNA.
• The ribosome helps form peptide bonds between the amino acids, creating a growing polypeptide chain which eventually folds into a functional protein.

This precise process is essential for the maintenance and function of life in all living organisms.