Slide 1
Each DNA strand guides a new complementary strand
Cells copy deoxyribonucleic acid, or DNA, before division so daughter cells can receive it. Each strand guides construction of a complementary new strand.
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This genetic material is usually called DNA. The resulting DNA molecules each contain an old strand paired with a newly made one, a pattern called semiconservative replication. This preserves a template while creating the material needed for the next generation of cells.
Slide 2
Polymerases add matching building blocks
DNA polymerases, the copying enzymes, add nucleotides, DNA’s building blocks, according to the template.
Correct base pairing makes appropriate additions more likely than mismatched ones.
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The polymerase also changes shape during selection, helping reject unsuitable nucleotides. Accuracy therefore depends on molecular recognition and enzyme dynamics, not just passive attraction between exposed bases.
Slide 3
Many copying enzymes remove recent mistakes
Many replicative polymerases can remove a wrongly added nucleotide before continuing. This proofreading reduces errors left in the new strand.
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The removal uses an exonuclease activity that works back from the growing end. It is a separate chemical action from extending the strand, allowing the enzyme to correct an error rather than merely stop at it.
Slide 4
Mismatch repair catches some remaining errors
Mismatch repair can detect errors that escaped initial polymerase selection and proofreading. Several mechanisms therefore contribute to copying fidelity.
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Damage to DNA is not identical to a copying mismatch. Cells have additional repair pathways for chemically altered bases and broken strands, matching different kinds of problems with different molecular machinery.
Slide 5
Changes can still survive into descendant cells
Some sequence changes remain despite these safeguards. If retained through later copying, they can become mutations in descendant cells.
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A change in a reproductive cell lineage can be inherited by offspring, while a change confined to another cell lineage is generally limited to that individual’s descendants of the affected cell.
Sources
- DNA Replication
National Human Genome Research Institute
- DNA Replication Mechanisms
NCBI Bookshelf