1. DNA Replication S phase of Interphase

2. DNA Replication DNA Replication DNA Replication occurs during the S phase of the INTERPHASE. STEP 1: Separation of the strands. DNA helicase - DNA helicase STEP 2: Assembly of the new strands. DNA polymerase - DNA polymerase

3. Step 1: Separation of Chains breaking the hydrogen bonds between nucleotides To copy DNA separate the two, adjoining chains (or backbones) by breaking the hydrogen bonds between nucleotides. DNA helicase. This action is assisted by the enzyme DNA helicase. replication fork Occurs at the replication fork. Occurs simultaneously at many points Occurs simultaneously at many points along the DNA strand.

4. Step 2: Assembly of New Strand DNA polymerase DNA polymerase brings complementary nucleotides to the new strand. Many DNA polymerases will bind at many different points along the nucleotide chains to speed up replication.

5. Accuracy of DNA Replication DNA replication is very accurate. Only one error occurs in 10,000 paired nucleotides. There are many enzymes that proofread and repair the DNA strands to keep the errors low. If errors remain un-repaired the production of proteins can be altered. **Holt Biology Interactive Tutor 6-3

6. What are MUTATIONS? mutation A mutation is the substitution of one nucleotide that is incorrect, and it can have serious effects in a cell. environmental carcinogen, DNA can become mutated beyond repair by many factors including environmental carcinogen, causing cancer or cell death. Types of point mutations Genetic Abnormalities Genetic Abnormalities