Chemistry-only: DNA is made from nucleotide monomers
| English | 中文 | Pinyin |
|---|---|---|
| nucleotide/ˈnjuːklɪɒtaɪd/ | 核苷酸 | hé gān suān |
| double helix/ˈdʌbl ˈhiːlɪks/ | 双螺旋 | shuāng luó xuán |
What would explain this observation?
- A DNA model has repeated building blocks along two chains. The order of its four nucleotide 核苷酸 types can encode information; it is not a chain made from amino acids or glucose.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- DNA, deoxyribonucleic acid, is a very large molecule essential for life. It encodes genetic instructions for the development and functioning of organisms and viruses. Most DNA molecules consist of two polymer chains arranged as a double helix 双螺旋. Each chain is built from nucleotide monomers. There are four nucleotide types, commonly identified by the bases A, T, C and G; a base alone is only part of the whole nucleotide.
- nucleotide: A monomer building block of a nucleic-acid chain, containing a sugar, phosphate and a base; double helix: The two-strand helical arrangement of the stated DNA model.
Which monomers form the two chains in the stated DNA model?
The chains provide a repeated structural framework while the sequence of nucleotide types varies. A ladder model can distinguish the two continuous chains from paired positions across them. In the familiar double-stranded DNA model, A pairs with T and C with G. Twisting that ladder models the double helix. Colour-coded blocks are a representation: they are not actual nucleotide shapes, accurate atom arrangements or a diagram of separate bases joined without a backbone.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- The chains provide a repeated structural framework while the sequence of nucleotide types varies. A ladder model can distinguish the two continuous chains from paired positions across them. In the familiar double-stranded DNA model, A pairs with T and C with G. Twisting that ladder models the double helix. Colour-coded blocks are a representation: they are not actual nucleotide shapes, accurate atom arrangements or a diagram of separate bases joined without a backbone.
- Build an actual classroom model with four labelled nucleotide-card types. Arrange a short sequence along one chain and the complementary sequence along the other, then twist or compare with a supplied three-dimensional model. State what the model shows about repeated units and variable sequence, and what it omits about dimensions and chemical bonds. No human DNA collection or biological sampling is necessary for this representation task.
Which two habits make the investigation or model in this case more defensible?
Build an actual classroom model with four labelled nucleotide-card types. Arrange a short sequence along one chain and the complementary sequence along the other, then twist or compare with a supplied three-dimensional model. State what the model shows about repeated units and variable sequence, and what it omits about dimensions and chemical bonds. No human DNA collection or biological sampling is necessary for this representation task.
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 short double-stranded model has 18 paired positions. Each position contains one nucleotide from each chain, so there are 18×2=36 nucleotides. If one chain contains six A, four T, five C and three G, its partner contains six T, four A, five G and three C. Counting the whole model therefore gives equal A/T and equal C/G totals, without claiming every DNA sequence has equal quantities of all four types.
A double-stranded DNA model has 24 paired positions. Count all its nucleotides. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A double-stranded DNA model has 24 paired positions. Count all its nucleotides.
The result is 48 nucleotides. Known: a short double-stranded model has 18 paired positions. Each position contains one nucleotide from each chain, so there are 18×2=36 nucleotides. If one chain contains six A, four T, five C and three G, its partner contains six T, four A, five G and three C. Counting the whole model therefore gives equal A/T and equal C/G totals, without claiming every DNA sequence has equal quantities of all four types.
Check the conclusion and its limits
- A nucleotide is not an amino acid, and four nucleotide types does not mean DNA is only four nucleotides long. A double helix has two polymer chains, not one chain split into four. Recognising DNA and its monomers is Chemistry-only content on both tiers. Additional molecular detail is an explanatory model, not a new requirement to reproduce advanced nucleotide chemistry.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
DNA is a polypeptide made from amino-acid monomers. This claim is false: A nucleotide is not an amino acid, and four nucleotide types does not mean DNA is only four nucleotides long. A double helix has two polymer chains, not one chain split into four. Recognising DNA and its monomers is Chemistry-only content on both tiers. Additional molecular detail is an explanatory model, not a new requirement to reproduce advanced nucleotide chemistry.
Chemistry-only: DNA is made from nucleotide monomers: The chains provide a repeated structural framework while the sequence of nucleotide types varies. A ladder model can distinguish the two continuous chains from paired positions across them. In the familiar double-stranded DNA model, A pairs with T and C with G. Twisting that ladder models the double helix. Colour-coded blocks are a representation: they are not actual nucleotide shapes, accurate atom arrangements or a diagram of separate bases joined without a backbone.
DNA is a polypeptide made from amino-acid monomers.
A nucleotide is not an amino acid, and four nucleotide types does not mean DNA is only four nucleotides long. A double helix has two polymer chains, not one chain split into four. Recognising DNA and its monomers is Chemistry-only content on both tiers. Additional molecular detail is an explanatory model, not a new requirement to reproduce advanced nucleotide chemistry.
A monomer building block of a nucleic-acid chain, containing a sugar, phosphate and a base: write the technical term.
nucleotide means A monomer building block of a nucleic-acid chain, containing a sugar, phosphate and a base.