1. Cell Growth and Division

2. The Cell Cycle What steps are taking place during the cell cycle? What types of cells go through the cell cycle? What do cells need for them to undergo cell growth and division?

3. The First Step of the Cell Cycle The first stage of the cell cycle is called interphase During interphase, the cell grows, makes a copy of its DNA, and prepares to divide into two new cells. Interphase has three main parts: growing, DNA replication, and preparing for division

4. Growing During this part of interphase cells grow to their full size and produce structures needed for their daily functions. What structures do you think the cell will focus on producing?

5. DNA Replication The second part of interphase is DNA replication. During this process cells make an exact copy of their DNA in their nuclei. Before we go into how DNA replication occurs let’s discuss what DNA is and where it is found in the cell.

6. DNA Structure To the right we see and image of DNA structure. DNA molecules look like a twisted ladder. What is this twisted ladder shape also known as? Each “rung” of the ladder is made up of a pair of nitrogen bases. Image courtesy of the U.S. National Library of Medicine

7. DNA Structure Nitrogen bases are molecules that contain the element nitrogen and other elements. The four nitrogen bases that build up DNA are: Adenine(A), Guanine(G), Cytosine(C), and Thymine(T) In DNA, Adenine can only pair with Thymine and Guanine can only be paired with Cytosine. This pairing pattern is key to understanding how DNA replication occurs.

8. DNA Replication During regular daily function, DNA is found within chromatin Chromatin is a combination of DNA and proteins and makes up the contents of the nucleus. Image courtesy of http://micro.magnet.fsu.edu/cells/nucleus/nucleus.html

9. The Replication Process Look at figure 15 on pg. 62 in your Cells and Heredity textbook During DNA replication the two sides of the DNA double helix will unwind and separate, like a zipper on your jacket. As the DNA “unzips”, nitrogen bases floating the nucleus will pair up with each half of the DNA molecule. Since nitrogen pairs need to match up with their partner nitrogen base, the newly formed DNA molecule will exactly match the original DNA molecule.

10. Preparation for Division The third and final step of interphase is the preparation for division This step occurs after DNA has been replicated. The cell will begin to produce structures that it will use to divide into two new daughter cells. At this point a cell is ready to divide.

11. BCR In your notebook answer the following question. Why do you think it’s important for DNA replication to occur before a cell can divide? Provide evidence to support your decision.