CHAPTER 12 NOTES

DNA REPLICATION

 

Definition: The process of copying DNA

 

Purpose: Gives new cells produced in mitosis and meiosis a complete set of chromosomes.

 

Where Does DNA Replication Occur?  Nucleus

 

When Does DNA Replication Occur? The S phase of interphase in the cell cycle

 

Steps of Replication:

1. DNA untwists and enzymes break the hydrogen bonds between the nitrogen bases. The DNA “unzips”.

2. Free-floating nucleotides pair with each unzipped strand following the base pairing rule (A with T and C with G). The complementary bases must match up!

·    Each strand of DNA acts a template.

·    DNA polymerase is an enzyme that joins the nucleotides together.

·    Hydrogen bonds hold the base pairs together.

3. the two new identical molecules of DNA are twisted back up by enzymes.

 

Note: In eukaryotic cells, replication may begin at dozens or hundreds of places on the DNA molecule and proceeds in both directions until the chromosome is completely copied.

 

Result: Two identical copies of DNA each composed of one original and one new strand.

 

Why is replication so important?

It occurs during interphase so that each new daughter cell will have a complete set of chromosomes at the end of mitosis.