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AP Biology Practice Quiz: DNA Replication

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: July 2026

Test your understanding with short quizzes. This quiz has 7 questions to check your progress.

Question 1 of 7

What is the fundamental purpose of DNA replication as described in the provided text?

All Questions (7)

What is the fundamental purpose of DNA replication as described in the provided text?

A) To create genetic mutations for evolution.

B) To ensure the continuity of genetic information for transmission between generations.

C) To synthesize proteins required for cellular function.

D) To break down old DNA molecules for energy.

Correct Answer: B

The provided content explicitly states that 'DNA replication ensures the continuity of genetic information' and is a mechanism for copying genetic information 'for transmission between generations.'

DNA replication is referred to as a 'semiconservative process.' What does this term imply about the resulting DNA molecules?

A) Each new DNA molecule is composed of two entirely new strands.

B) Each new DNA molecule consists of one original strand and one newly synthesized strand.

C) Only half of the original DNA molecule is copied, while the other half is discarded.

D) The original DNA molecule remains intact, and a second, completely new molecule is created.

Correct Answer: B

The term 'semiconservative' means that half of the original molecule is conserved. In DNA replication, this means each of the two new double helices contains one parental (original) strand and one new strand.

According to the principles of DNA replication, in which direction does the synthesis of a new DNA strand occur?

A) From the 3' end to the 5' end.

B) From the 5' end to the 3' end.

C) In both directions from the origin of replication.

D) The direction is random and depends on the specific gene being copied.

Correct Answer: B

The provided content clearly states that DNA is 'synthesized in the 5' to 3' direction.' This is a fundamental rule of DNA replication.

Which of the following enzymes is primarily responsible for unwinding and separating the two strands of the DNA double helix at the start of replication?

A) DNA polymerase

B) Ligase

C) Helicase

D) Topoisomerase

Correct Answer: C

While the content lists several enzymes, helicase's specific function is to unwind the DNA helix, separating the two parental strands to make them available as templates for replication.

The enzyme DNA polymerase is essential for replication because it performs which of the following actions?

A) It relieves the strain from supercoiling ahead of the replication fork.

B) It joins the fragments of the newly synthesized lagging strand.

C) It adds new nucleotides to the 3' end of the growing DNA strand, following the template.

D) It unwinds the parental DNA double helix.

Correct Answer: C

DNA polymerase is the main enzyme for synthesis. It reads the template strand and adds complementary nucleotides to the 3' end of the new strand, thereby extending it in the 5' to 3' direction.

A cell develops a mutation that renders its topoisomerase enzyme nonfunctional. Which of the following would be the most likely immediate consequence during DNA replication?

A) The two DNA strands would fail to separate at the origin of replication.

B) The newly synthesized DNA fragments would not be joined together.

C) Supercoiling and torsional strain would build up ahead of the replication fork, halting the process.

D) The new DNA strand would be synthesized in the 3' to 5' direction.

Correct Answer: C

Topoisomerase works ahead of the replication fork to relieve the strain caused by the unwinding action of helicase. Without a functional topoisomerase, the DNA would become overly twisted, preventing replication from proceeding.

Which statement correctly pairs two of the enzymes involved in DNA replication with their respective functions?

A) Helicase synthesizes the new DNA strand, while DNA polymerase unwinds the helix.

B) Ligase separates the DNA strands, while topoisomerase joins them.

C) DNA polymerase synthesizes the new DNA strand, and ligase joins DNA fragments.

D) Topoisomerase adds new nucleotides, and helicase joins DNA fragments.

Correct Answer: C

This option correctly identifies the primary roles of two key enzymes mentioned in the text. DNA polymerase is the main builder of the new DNA strand, and ligase is responsible for joining DNA fragments (such as Okazaki fragments on the lagging strand).