Higher Tier: sequence, protein shape and gene expression
| English | Français |
|---|---|
| protein synthesis/ˈprəʊtiːn ˈsɪnθəsɪs/ | synthèse des protéines |
| gene expression/dʒiːn ekˈspreʃn/ | expression génique |
What would explain this observation?
- Higher Tier: A DNA change can alter a protein’s shape, leave its function unchanged, or change how much protein is made. These are different causal routes.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Complementary DNA strands pair A with T and C with G. Proteins are synthesised on ribosomes according to a template. Carrier molecules bring specific amino acids, which join in the correct order. The completed chain folds into a unique shape suited to its function, such as an enzyme, a hormone or a structural protein including collagen.
- protein synthesis 蛋白质合成: Assembly of an amino-acid chain on a ribosome according to a template; gene expression 基因表达: Use of genetic information to produce a functional product.
Which account fits a non-coding regulatory variant?
A change in coding DNA can change the amino-acid sequence and therefore folding. An enzyme’s active site may no longer fit its substrate, or a structural protein may lose strength. Most mutations do not change the protein, or change it too little to alter its appearance or function. Non-coding DNA can control whether genes are switched on or off; variants there may affect expression without changing the coded amino-acid sequence.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A change in coding DNA can change the amino-acid sequence and therefore folding. An enzyme’s active site may no longer fit its substrate, or a structural protein may lose strength. Most mutations do not change the protein, or change it too little to alter its appearance or function. Non-coding DNA can control whether genes are switched on or off; variants there may affect expression without changing the coded amino-acid sequence.
- Use supplied short sequences and an explicit classroom code key. First distinguish a coding-region change from an expression-control change, then trace only the consequence supported by the prompt. Detailed structures of mRNA, tRNA, amino acids and proteins are not required. Model substitutions or insertions with cards rather than treating all mutations as harmful.
Which two habits make the investigation or model in this case more defensible?
Use supplied short sequences and an explicit classroom code key. First distinguish a coding-region change from an expression-control change, then trace only the consequence supported by the prompt. Detailed structures of mRNA, tRNA, amino acids and proteins are not required. Model substitutions or insertions with cards rather than treating all mutations as harmful.
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: a supplied strand is A C G T. Its complementary sequence is T G C A in the paired display. In a separate fictional sample, 4 of 80 observed variants alter the measured phenotype: 4/80×100 = 5%. These supplied frequencies do not establish a universal mutation rate or prove the remaining variants have no effect in every environment.
Five of 100 variants in a fictional study alter the measured phenotype. Find the percentage. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
Five of 100 variants in a fictional study alter the measured phenotype. Find the percentage.
The result is 5 %. Known: a supplied strand is A C G T. Its complementary sequence is T G C A in the paired display. In a separate fictional sample, 4 of 80 observed variants alter the measured phenotype: 4/80×100 = 5%. These supplied frequencies do not establish a universal mutation rate or prove the remaining variants have no effect in every environment.
Check the conclusion and its limits
- DNA does not assemble the protein directly inside the nucleus in this account: synthesis takes place on ribosomes. A changed sequence does not automatically create a useful or harmful phenotype. Non-coding means not coding a protein, not having no function.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Every mutation changes protein shape and causes disease. This claim is false: DNA does not assemble the protein directly inside the nucleus in this account: synthesis takes place on ribosomes. A changed sequence does not automatically create a useful or harmful phenotype. Non-coding means not coding a protein, not having no function.
Higher Tier: sequence, protein shape and gene expression: A change in coding DNA can change the amino-acid sequence and therefore folding. An enzyme’s active site may no longer fit its substrate, or a structural protein may lose strength. Most mutations do not change the protein, or change it too little to alter its appearance or function. Non-coding DNA can control whether genes are switched on or off; variants there may affect expression without changing the coded amino-acid sequence.
Every mutation changes protein shape and causes disease.
DNA does not assemble the protein directly inside the nucleus in this account: synthesis takes place on ribosomes. A changed sequence does not automatically create a useful or harmful phenotype. Non-coding means not coding a protein, not having no function.
Assembly of an amino-acid chain on a ribosome according to a template: write the technical term.
protein synthesis means Assembly of an amino-acid chain on a ribosome according to a template.