DNA, protein synthesis and evidence
| English | 中文 | Pinyin |
|---|---|---|
| transcription/trænˈskrɪpʃn/ | 转录 | zhuǎn lù |
| translation/trænˈsleɪʃn/ | 翻译 | fān yì |
What would explain this observation?
- A change in DNA can affect a protein, but not every DNA change changes the amino-acid sequence. The effect depends on the sequence and how it is used.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- DNA stores information in a base sequence. Complementary base pairing supports copying. During gene expression, transcription 转录 makes RNA and translation 翻译 uses codons to assemble an amino-acid sequence.
- transcription: Formation of RNA using a DNA template; translation: Formation of a polypeptide using an mRNA sequence.
Which change can leave the amino-acid sequence unchanged?
A codon comprises three bases. The genetic code is degenerate: more than one codon can specify the same amino acid. A substitution can therefore be silent, while insertions or deletions can shift the reading frame.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A codon comprises three bases. The genetic code is degenerate: more than one codon can specify the same amino acid. A substitution can therefore be silent, while insertions or deletions can shift the reading frame.
- Keep DNA template, coding DNA and mRNA distinct. State the strand used and write sequences in the required direction. Use a codon table for mRNA, not an unexplained DNA triplet.
Which two habits make the investigation or model in this case more defensible?
Keep DNA template, coding DNA and mRNA distinct. State the strand used and write sequences in the required direction. Use a codon table for mRNA, not an unexplained DNA triplet.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: an mRNA coding region contains 90 bases, including one stop codon. Codons = bases/3 = 90/3 = 30. A stop codon does not encode an amino acid, so the peptide contains 29 amino acids under this stated model.
A coding mRNA segment has 63 bases including a stop codon. Find peptide length. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A coding mRNA segment has 63 bases including a stop codon. Find peptide length.
The result is 20 amino acids. Known: an mRNA coding region contains 90 bases, including one stop codon. Codons = bases/3 = 90/3 = 30. A stop codon does not encode an amino acid, so the peptide contains 29 amino acids under this stated model.
Check the conclusion and its limits
- The number of bases is not automatically the number of amino acids. Real genes include regulatory regions and, in eukaryotes, often introns; a whole gene length is not a peptide-length calculation.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Each DNA base encodes one complete amino acid. This claim is false: The number of bases is not automatically the number of amino acids. Real genes include regulatory regions and, in eukaryotes, often introns; a whole gene length is not a peptide-length calculation.
DNA, protein synthesis and evidence: A codon comprises three bases. The genetic code is degenerate: more than one codon can specify the same amino acid. A substitution can therefore be silent, while insertions or deletions can shift the reading frame.
Each DNA base encodes one complete amino acid.
The number of bases is not automatically the number of amino acids. Real genes include regulatory regions and, in eukaryotes, often introns; a whole gene length is not a peptide-length calculation.
Formation of RNA using a DNA template: write the technical term.
transcription means Formation of RNA using a DNA template.