AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
Translation as the production of polypeptides from the sequence of codons…
Full specification wording
DNA and protein synthesis: Translation as the production of polypeptides from the sequence of codons carried by mRNA. The roles of ribosomes, tRNA and ATP.
Translation builds a polypeptide from the codons on mRNA.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 6 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Translation builds a polypeptide from the codons on mRNA. The mRNA binds to a ribosome, which holds two codons at a time. A tRNA whose anticodon is complementary to the first codon binds by hydrogen bonds, carrying one specific amino acid; a second tRNA binds at the adjacent codon. A peptide bond forms between the two amino acids, catalysed by the ribosome. The first tRNA detaches and is reused, and the ribosome moves along exactly three bases to the next codon. The cycle repeats until a stop codon is reached, when the completed polypeptide is released and folds into its tertiary structure. ATP is required to attach each amino acid to its tRNA (amino acid activation) and provides energy for the process; peptide bond formation is catalysed by the ribosome.
What earns the marks
- mRNA binds to a ribosome and the bases are read in triplets as codons.
- tRNA anticodons bind to complementary mRNA codons by hydrogen bonds, each tRNA carrying a specific amino acid.
- Peptide bonds form between adjacent amino acids, catalysed by the ribosome.
- The ribosome moves along the mRNA to the next codon, with tRNA released and reused.
- The process continues to a stop codon, after which the polypeptide folds into its tertiary structure.
- ATP is used to attach each amino acid to its tRNA and provides energy for translation; peptide bond formation is catalysed by the ribosome.
Common mistakes and how to put them right
Saying the tRNA anticodon is complementary to the DNA rather than to the mRNA codon.
Describing the ribosome as 'reading' the mRNA with no mention of tRNA or anticodons.
Stating that ATP directly drives peptide bond formation or ribosome movement.
Put it right: ATP charges each amino acid onto its tRNA and provides energy for translation, while peptide bonds are catalysed by the ribosome.
Writing that hydrogen bonds join the amino acids, when peptide bonds join amino acids and hydrogen bonds hold codon to anticodon.
Saying a changed anticodon stops the protein being made, when it inserts a different amino acid and alters the tertiary structure.
Exam tips
- Name the bond at every stage: hydrogen bonds for codon-anticodon, peptide bonds between amino acids.
- To link a tRNA mutation to a disease, use the chain: wrong amino acid, altered tertiary structure, protein cannot carry out its function.
Try the lesson
The start of the DNA and protein synthesis: Translation as the production of polypeptides from the sequence of codons carried by mRNA. The roles of ribosomes, tRNA and ATP. lesson, made from checked teaching notes for this specification point.
Have a go first
Which molecule carries the amino acid to the ribosome during translation?
Listen
Translation builds a polypeptide from the codons on mRNA. The mRNA binds to a ribosome, which holds two codons at a time. A tRNA whose anticodon is complementary to the first codon binds by hydrogen bonds, carrying one specific amino acid; a second tRNA binds at the adjacent codon. A peptide bond forms between the two amino acids, catalysed by the ribosome. The first tRNA detaches and is reused, and the ribosome moves along exactly three bases to the next codon. The cycle repeats until a stop codon is reached, when the completed polypeptide is released and folds into its tertiary structure. ATP is required to attach each amino acid to its tRNA (amino acid activation) and provides energy for the process; peptide bond formation is catalysed by the ribosome. A strong answer earns marks for these points. mRNA binds to a ribosome and the bases are read in triplets as codons. tRNA anticodons bind to complementary mRNA codons by hydrogen bonds, each tRNA carrying a specific amino acid. peptide bonds form between adjacent amino acids, catalysed by the ribosome. the ribosome moves along the mRNA to the next codon, with tRNA released and reused. A common slip: stating that ATP directly drives peptide bond formation or ribosome movement. Instead, ATP charges each amino acid onto its tRNA and provides energy for translation, while peptide bonds are catalysed by the ribosome. Exam tip: Name the bond at every stage: hydrogen bonds for codon-anticodon, peptide bonds between amino acids.
Key words
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codons and anticodons
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ribosome movement
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peptide bond formation
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role of ATP
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See every definition
- codons and anticodons
- The bases on mRNA are read in triplets as codons, and a tRNA anticodon binds to a complementary mRNA codon by hydrogen bonds.
- ribosome movement
- The ribosome moves along the mRNA to the next codon, and the tRNA is released and reused.
- peptide bond formation
- Peptide bonds form between adjacent amino acids, catalysed by the ribosome.
- role of ATP
- ATP is used to attach each amino acid to its tRNA and provides energy for translation.
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