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MCAT Content / Genetic Code / Codon Anticodon Relationship

Codon–anticodon relationship

Topic: Genetic Code

When mRNA is translated into a polypeptide chain during translation, the codons of mRNA base pair with complementary RNA sequences in tRNA molecules (which carry amino acids to the growing polypeptide) at the ribosome.

mRNA molecules contain triplets of nucleotides known as codons, each of which codes for an amino acid or a stop signal for translation. tRNA molecules also contain triplets of nucleotides, known as anticodons, which are complementary to codons. Take a look at the figure below to see the structure of a tRNA molecule and the location of the anticodon (grey) relative to the site where amino acids attach to the molecule (yellow):

During translation, tRNA molecules recognize the codons in the mRNA through base pairing between the codon and anticodon. This ensures that correct the amino acid, based on the mRNA sequence, is added to the growing polypeptide chain. Take a look at an example of codon-anticodon pairing in the image below:

MCAT Codon–anticodon relationship


Practice Questions

Khan Academy

MCAT Official Prep (AAMC)

Practice Exam 1 B/B Section Passage 6 Question 32

Practice Exam 1 B/B Section Question 59

Practice Exam 4 B/B Section Passage 2 Question 14

Practice Exam 4 B/B Section Question 57


Key Points

• mRNA codons and tRNA anticodons are complementary to each other.

• Codons in the mRNA bind to the anticodons in the tRNA during protein synthesis (translation).

• This relationship ensures the correct the amino acids are added to the growing polypeptide chain.

Key Terms

Messenger RNA (mRNA): An RNA molecule, copied from a DNA sequence, that encodes a polypeptide sequence (protein); three consecutive nucleotides constitute a codon.

Polypeptide: A chain of amino acids that are connected by peptide bonds.

Translation: The process by which an mRNA molecule is used to create a polypeptide (protein).

Complementary: Describes the pairing between specific nucleotides in DNA and RNA.

Transfer RNA (tRNA): An RNA molecule, copied from a DNA sequence, that carries amino acids to the ribosome during translation.

Amino acids: Organic molecules that make up proteins; they contain an amino group (−NH2), a carboxyl group (−COOH), and a side chain specific to each amino acid.

Ribosome: A macromolecule made up of RNA and proteins that acts as the site of protein synthesis during translation.

Anticodons: he triplet of nucleotides in tRNA that is complementary to a mRNA codon and allows a tRNA to recognize specific codons during translation.

Codon-anticodon pairing: Describes the pairing between mRNA codons and complementary tRNA anticodons that allows tRNA molecules to recognize codons and add the correct amino acids to a growing polypeptide chain.

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