1. DNA Replication Why does the DNA in a cell replicate before cell division?

2. DNA Replication A cell makes a copy of its DNA before mitosis occurs. DNA replication ensures that each daughter cell will have all of the genetic information it needs to carry out its activities.

3. History 1950’s Discovered DNA carries all of the cell’s instructions. DNA passed from parent to daughter cells 1953 – Watson and Crick figured out the structure of DNA by building the DNA molecule. Discovery revealed important information about how DNA copies itself

4. Structure of DNA Double Helix – a twisted ladder shape or sometimes known as a spiral staircase. Two sides of ladder – Made of a combination of alternating deoxyribose (sugar) molecules and phosphate molecules. Rungs of ladder – made of Nitrogen bases

5. Nitrogen Bases Adenine – A Thymine – T Guanine – G Cytosine – C Adenine always pairs with Thymine Guanine always pairs with Cytosine The pairing pattern of the nitrogen bases is the key to understanding how DNA replication occurs.

6. Replication Process DNA Replication begins when the 2 sides of the DNA molecule unwind and separate like a zipper unzipping. The DNA molecule separates between the paired nitrogen bases on each rung of the ladder. Nitrogen bases that are floating in the nucleus pair up with the bases on each half of the DNA molecule. A combines with T G combines with C

7. DNA Replication

8. Replication Process Two new DNA molecules are formed. The order of the bases in each new DNA molecules will exactly match the order in the original DNA molecules.