1. Reviewing Nitrogen Base Pairs Which nitrogenous base always pairs with Cytosine (C)? _______________________ Which nitrogenous base always pairs with Adenine (A)?

2. Reviewing Nitrogen Base Pairs A double-stranded segment of DNA is 50 nucleotides long. – If 30 of the bases are adenine how many are thymine?_______ – How many are cytosine?________ – How many are guanine? ________

3. DNA Replication 1. What is DNA replication? 1a. The process in which a cell makes a copy of its DNA before dividing.

4. DNA Replication 2. What are the steps of DNA replication? Step 1: Frist the DNA strand has to split down the middle. An enzyme called helicase “unzips” the DNA molecule by breaking the weak hydrogen bonds between the complimentary base pairs.

5. DNA Replication 2. What are the steps of DNA replication? Step 2: New complimentary base pairs are attached to each strand. Other enzymes, called DNA polymerase, move along the bases on one of the unzipped halves and connect the complementary nucleotides. Because of the base pairing rule, only the correct, complimentary bases will fit.

6. DNA Replication 2. What are the steps of DNA replication? Step 3: Meanwhile, another DNA polymerase does the same thing to the other half of the original molecule.

7. DNA Replication 2. What are the steps of DNA replication? When it is finished, the nucleus has two identical copies of the original DNA molecule.

8. DNA Replication 2. What are the steps of DNA replication? Now the cell can proceed with mitosis. Each completed DNA molecule travels to opposite sides of the cell, which then divides.

9. https://www.youtube.com/watch?v=4jtmOZalvS0 https://www.youtube.com/watch?v=zdDkiRw1Pd U&feature=related