How Does DNA Replicate?

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  • 0:01 How Does DNA Replicate?
  • 0:54 Steps of Replication
  • 1:49 Rates of Replication
  • 2:24 Proofreading
  • 3:02 Lesson Summary
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Lesson Transcript
Instructor: Jayne Yenko

Jayne has taught health/nutrition and education at the college level and has a master's degree in education.

In this lesson, we will learn why DNA replicates as well as how. We'll also learn about the rates of replication and how DNA proofreads itself. After watching the lesson, you can complete a short quiz to test your knowledge.

How Does DNA Replicate?

DNA (deoxyribose nucleic acid) carries all the genetic information needed to re-create itself and to pass on the characteristics of the organism. When a cell reproduces, it needs to pass all of this genetic information on to the new cells. Before reproduction can take place, a cell must replicate, or copy, its DNA.

The structure of the DNA molecule makes replication easy. Each side of the double helix run in opposite directions - one up, one down. This gives the structure the ability to unzip down the middle, and each side serves as a template for the other side. During actual replication, the helix doesn't unzip completely. A smaller area, called a replication fork, is unzipped instead.

Steps of Replication

What are the steps of replication?

  1. An enzyme, DNA gyrase, separates each side of the double helix.
  2. Another enzyme, helicase, unwinds the double helix.
  3. Several small proteins temporarily bind to each side and keep the sides separated.
  4. An enzyme complex, DNA polymerase, walks down the DNA strands and adds new nucleotides to each strand. The nucleotides pair up: adenine (A) with thymine (T) and guanine (G) with cytosine (C).
  5. A subunit of the DNA polymerase proofreads the new DNA.
  6. An enzyme, DNA ligase, seals up the fragments into long continuous strands.
  7. The new copies automatically wind up again.

Rates of Replication

Different types of cells replicate at different rates. Some, like those in hair, fingernails, and bone marrow, divide constantly. Others, like those in the heart, muscles, and brain, go through several rounds of replication and cell division and then stop. Some others, such as skin and liver cells, stop replicating and dividing but will start again to repair injuries. For cells that do not constantly divide, the cues to tell them to divide come in the form of chemicals, such as hormones, or from the environment.

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