Question

What is a codon?

Short answer

A codon is a sequence of three nucleotides in mRNA that specifies a particular amino acid or a start/stop signal during protein synthesis.

Step-by-step solution

Understand the Genetic Code

The genetic code is a set of rules by which information encoded in DNA or RNA sequences is translated into proteins by living cells. In particular, a genetic code defines how sequences of three nucleotides, known as triplets, specify which amino acid will be added next during protein synthesis.

Define a Nucleotide

Nucleotides are the building blocks of nucleic acids like DNA and RNA. Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base (adenine [A], cytosine [C], guanine [G], or thymine [T] in DNA, uracil [U] replacing thymine in RNA).

Introduce the Triplet Codon

A codon is a sequence of three nucleotides in mRNA that encodes a specific amino acid or a start/stop signal during translation. The sequence determines which amino acid is added to the growing protein chain.

Explain Codons in Protein Synthesis

During protein synthesis, the ribosome reads the mRNA sequence in sets of three nucleotides or codons. Each codon corresponds to one of the 20 amino acids or a stop signal, which causes the synthesis to terminate.

Key concepts

Understanding the Genetic Code

The genetic code is the blueprint for how living cells translate DNA or RNA sequences into proteins. It comprises sets of three nucleotides called triplets. Each triplet specifies which amino acid will be added next in the process of protein synthesis. These triplet sequences are fundamental for the creation of proteins, which are essential for various cell functions.
For example, the triplet sequence 'AUG' codes for the amino acid methionine, a crucial molecule that often signals the start of protein synthesis. Without the genetic code, cells would not be able to produce the proteins necessary for life.
In essence, the genetic code is like a detailed instruction manual that tells the cell machinery how to assemble proteins, step by step.

The Building Blocks: Nucleotides

Nucleotides are the basic units that make up nucleic acids like DNA and RNA. Each nucleotide is composed of three parts: a sugar, a phosphate group, and a nitrogenous base. In DNA, the nitrogenous bases are adenine (A), cytosine (C), guanine (G), and thymine (T). In RNA, thymine is replaced by uracil (U).
Nucleotides form the backbone of the DNA and RNA strands through sugar-phosphate connections. These sequences of nucleotides carry genetic information.
When these nucleotides are read in sets of three, the sequence forms a codon, which instructs the cell's machinery during protein synthesis.

Decoding Protein Synthesis

Protein synthesis is the process by which cells create proteins based on the genetic information found in DNA and carried by RNA. This process takes place in the ribosome, a cellular machine that reads the mRNA sequence in triplets or codons.
Each codon corresponds to a specific amino acid or a stop signal, which tells the ribosome when to stop synthesizing the protein. For example:

• The codon 'GCU' codes for the amino acid alanine.
• The codon 'UAA' is a stop signal, indicating the end of the protein chain.

As the ribosome reads the mRNA, it adds the corresponding amino acids to the growing protein chain, creating a unique protein based on the original DNA template.
Protein synthesis is a highly regulated and precise process, ensuring that each cell produces the right proteins needed for its functions, from muscle contraction to enzyme activity.