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Genetic Code and Translation

The genetic code is the set of triplet codons in mRNA that specify amino acids, and translation is the ribosome-mediated synthesis of a polypeptide using mRNA, tRNA, and amino acids.

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Student-friendly explanation

The genetic code is triplet, nearly universal, non-overlapping, comma-less, and degenerate, meaning more than one codon can code for the same amino acid. AUG usually acts as the start codon and codes for methionine, while UAA, UAG, and UGA are stop codons. tRNA works as an adapter because it has an anticodon for mRNA recognition and an amino acid attachment site. During translation, charged tRNA brings amino acids to the ribosome. Codon-anticodon pairing at ribosomal sites ensures amino acids are added in the correct order to form a polypeptide.

How to write this in exams

  1. 1

    Start with the exact idea

    The genetic code is the set of triplet codons in mRNA that specify amino acids, and translation is the ribosome-mediated synthesis of a polypeptide using mRNA, tRNA, and amino acids.

  2. 2

    Then show how to use it

    Attach amino acid to tRNA, bind mRNA to ribosome, start at AUG, match codon with anticodon at A site, form peptide bond with chain at P site, move ribosome, repeat elongation, stop at termination codon.

  3. 3

    Add one concrete example

    The mRNA codon AUG begins translation and brings methionine. If the next codon is UUU, a tRNA with complementary anticodon carries phenylalanine to the ribosome.

  4. 4

    Avoid this incomplete answer

    Saying stop codons code for a special amino acid.

Definition

The genetic code is the set of triplet codons in mRNA that specify amino acids, and translation is the ribosome-mediated synthesis of a polypeptide using mRNA, tRNA, and amino acids.

Example

The mRNA codon AUG begins translation and brings methionine. If the next codon is UUU, a tRNA with complementary anticodon carries phenylalanine to the ribosome.

Rule to remember

Coding rule: three bases form one codon; codons are read sequentially in one reading frame from start codon to stop codon.

Memory hook

Codon says the word, anticodon answers it, ribosome links the amino acids.

Examples and method

Worked example

An mRNA segment with 5'-AUG GGU UAA-3' starts with methionine, adds glycine, then stops at UAA, producing a short polypeptide before termination.

Method to apply

Attach amino acid to tRNA, bind mRNA to ribosome, start at AUG, match codon with anticodon at A site, form peptide bond with chain at P site, move ribosome, repeat elongation, stop at termination codon.

Diagram support

Label mRNA, codon, tRNA, anticodon, amino acid attachment site, ribosome small and large subunits, A site, P site, and growing polypeptide chain.

How CBSE asks it

Asked as features of genetic code, codon interpretation, tRNA structure-function, or translation sequence.

Avoid common mistakes

Common confusion

Students often write that one amino acid has only one codon. The code is degenerate, so several codons may specify the same amino acid.

Common wrong answer

Saying stop codons code for a special amino acid.

Exam tip

For translation answers, mention mRNA codon, tRNA anticodon, aminoacylation, ribosome, initiation, elongation, termination, and peptide bond formation.

Quick check

Why is tRNA called an adapter molecule?

tRNA is called an adapter because one part recognizes the mRNA codon through its anticodon, while another part carries the specific amino acid for that codon.

Answer writing and exam use

1-mark answer

Define genetic code, list key features, explain tRNA as adapter, then describe translation through initiation, elongation, and termination with codon-anticodon pairing.

2-mark answer

Define genetic code, list key features, explain tRNA as adapter, then describe translation through initiation, elongation, and termination with codon-anticodon pairing.

3-mark answer

Define genetic code, list key features, explain tRNA as adapter, then describe translation through initiation, elongation, and termination with codon-anticodon pairing.
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