Molecular Biology

DNA Replication

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Session Overview


This session will explain how DNA is replicated prior to cell division. In this process, DNA polymerase uses an original strand as a template to create a new daughter strand of DNA. Polymerization occurs in the 5’ to 3’ direction, creating a new strand that is anti-parallel to the original. Polymerization begins at a specific DNA sequence called the Origin of Replication and proceeds in two directions along both template strands. Because of the directionality of synthesis, one strand is synthesized continuously, while the other strand is synthesized in small fragments, which are then joined together by DNA ligase.

Learning Objectives

  • To understand the semi-conservative model of DNA replication.
  • To recognize the 5’ and 3’ ends of DNA and predict the direction in which replication will proceed.
  • To predict the sequence of a newly synthesized strand of DNA, based on the sequence of the original strand.
  • To identify the leading and lagging strands during replication.
  • To understand the function of helicase and DNA ligase and explain why they are necessary.

Session Activities

Lecture Video

Watch the lecture video excerpt

Check Yourself

Below is a representation of an origin of replication and the two associated replication forks. Synthesis of new DNA occurs on both strands.


Question 1

At Fork 1, which template strand (1 or 2) is copied in a continuous manner?

Template strand 1 check
Template strand 2 close

Question 2

To which site or sites can the primer 5'-CAAGG-3' bind to initiate replication?

All Sites close
Only Site A close
Only Site B close
Only Site C close
Only Site D close
Sites A and B close
Sites B and D check

Session Activities

Help Session Video

Watch the short video of Sera Thornton explaining the numbering and labeling conventions of RNA and of proteins.

Practice Problems

Further Study

Suggested topics for further study in an introductory-level Biology textbook

  • DNA Replication

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Learning Resource Types

theaters Recitation Videos
assignment_turned_in Problem Sets with Solutions
grading Exams with Solutions
theaters Lecture Videos