Cell Growth and Division

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?

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

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?

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.

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

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.

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

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.

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.

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.