DNA replication: retain one strand in each daughter molecule
הוצג| English | משמעות |
|---|---|
| DNA polymerase/ˌdiː en ˈeɪ ˌpɒlɪməˈreɪz/ | DNA פולימראז |
| semi-conservative replication/ˈsemi kənˈsɜːvətɪv ˌreplɪˈkeɪʃn/ | ריפוי חצי-שמרני |
What would explain this observation?
- After DNA replication, each daughter double helix contains one pre-existing strand and one newly synthesized strand. Copying a molecule is different from expressing its information.
Build the model
- DNA replication is semi-conservative.
- Complementary base pairing supports copying of the base sequence: adenine pairs with thymine and cytosine with guanine.
- The strands have opposite orientations.
- Helicase separates paired strands, while DNA polymerase DNA聚合酶 builds new DNA using a template and available nucleotides.
- semi-conservative replication 半保留复制: DNA copying in which each daughter double helix retains one parental strand.
- DNA polymerase: An enzyme that synthesizes DNA using a template.
What does each daughter double helix retain after one ideal replication round?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Replication is semi-conservative: each daughter double helix keeps one parental strand paired with one new strand. Keeping both parental strands together in every molecule, or none, contradicts the labelling evidence.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- New DNA is synthesized in the 5′ to 3′ direction.
- In a simplified fork model, one new strand can be synthesized continuously while the other is produced in fragments that are joined.
- Distinguish these molecular mechanisms from the later separation of chromosomes during cell division.
- Copying errors can occur despite proofreading and repair.
In the lab: Use labelled strand models or an attributed experimental diagram. Mark old and new material with both labels and colours so the meaning survives monochrome viewing. Track successive rounds using a stated starting population and assumptions. A classroom model illustrates predictions; it is not direct evidence about enzyme activity or a substitute for experimental results.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: one double-stranded molecule contains two labelled original strands.
- After one complete round in unlabelled nucleotides, two molecules each contain one labelled strand.
- After two rounds, four molecules exist: two retain one labelled original strand and two contain only unlabelled strands.
- The fraction containing an original strand is 2/4=50%.
Your turn: One labelled double helix replicates for three complete rounds in unlabelled nucleotides. What percentage of the eight molecules contain an original strand?
One labelled double helix replicates for three complete rounds in unlabelled nucleotides. What percentage of the eight molecules contain an original strand?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 25 %. Known: one labelled double helix; three complete rounds in unlabelled nucleotides; 2^3 = 8 molecules. Only the two original strands persist, each in one molecule, so 2 of 8 molecules contain an original strand. Percentage = 2/8 x 100 = 25%.
Check the conclusion and its limits
- Replication uses DNA as a template to make DNA; transcription uses a DNA template to make RNA.
- A predicted label distribution assumes complete rounds and no degradation or exchange of the labelled material.
Not true: DNA replication and transcription both produce the same type of nucleic-acid product. Replication copies DNA into DNA; transcription copies a DNA template into RNA. The products are different nucleic acids with different roles.
- DNA replication is semi-conservative.
- New DNA is synthesized in the 5′ to 3′ direction.
- Watch for: replication uses DNA as a template to make DNA; transcription uses a DNA template to make RNA.
Write from 2 labelled molecules out of 32
- One labelled double helix replicates for 5 complete rounds in unlabelled nucleotides.
- Say how many of the 32 molecules still contain an original strand.
Replication copies DNA into DNA; transcription copies a DNA template into RNA.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. Replication copies DNA into DNA; transcription copies a DNA template into RNA. The products are different nucleic acids with different roles.
DNA copying in which each daughter double helix retains one parental strand: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
semi-conservative replication means DNA copying in which each daughter double helix retains one parental strand.
One labelled double helix replicates for 5 complete rounds in unlabelled nucleotides. How many molecules are there, and what fraction still contain an original strand?
2 to the power 5 is 32. Two original strands remain in two molecules, so the fraction is 2 out of 32.
After 5 rounds, what fraction of the molecules contain an original strand?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Five rounds make 32 molecules, and the two original strands are in 2 of them.