AP Biology Unit 6 Topic 2: DNA replication

What to Know

Replication is semiconservative because each DNA molecule contains one original strand and one newly built strand.
DNA polymerase adds nucleotides only in the 5 prime to 3 prime direction.
The leading and lagging strands are built differently because DNA strands run antiparallel.
Always connect this topic back to the larger unit: Gene Expression and Regulation.

Detailed Notes

DNA replication belongs to Unit 6: Gene Expression and Regulation. DNA replication copies genetic information by using each original strand as a template for a new complementary strand. Treat the topic as a relationship between structure, process, evidence, and biological function instead of memorizing an isolated definition.

Key relationships: Replication is semiconservative because each DNA molecule contains one original strand and one newly built strand. DNA polymerase adds nucleotides only in the 5 prime to 3 prime direction. The leading and lagging strands are built differently because DNA strands run antiparallel.

Model to use: Draw a replication fork and label helicase action, primer placement, leading strand synthesis, and lagging strand fragments. A clear model should label the parts, show the direction of movement or information flow when relevant, and connect the diagram back to the biological outcome.

AP-style move: When a replication enzyme is disrupted, predict whether unwinding, primer formation, strand extension, or fragment joining is affected. Strong answers name the concept, apply it to the scenario, and explain the reasoning in complete sentences.

Key Vocabulary

Semiconservative replication

DNA copying in which each new double helix contains one old strand and one new strand.

Replication fork

The Y-shaped region where DNA strands separate and copying occurs.

DNA polymerase

An enzyme that adds DNA nucleotides to a growing strand.

Primer

A short nucleic acid segment that provides a starting point for DNA synthesis.

Leading strand

The new DNA strand synthesized continuously toward the replication fork.

Lagging strand

The new DNA strand synthesized discontinuously away from the replication fork.

Quick Practice

How would you explain DNA replication in one or two AP-style sentences?

Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.

Official Alignment

Reference and Attribution

Biology concept reference: Biology for AP Courses by OpenStax, Rice University. Access for free at OpenStax. Licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License. EduCompanion used this source as a conceptual reference and rewrote the study notes in original wording.