1. Discover Activity: What are the Yeast Cells Doing?
Ch Cell Division Key Concepts: What events take place during the three stages of the cell cycle? How does the structure of DNA help account for the way in which DNA copies itself?
Discover Activity: What are the Yeast Cells Doing?
Use a plastic dropper to transfer some yeast cells from a yeast culture to a microscope slide. Add a coverslip and place the slide under a microscope.
Examine the cells on the slide. Draw what you see.
2. What process do you think the “double cells” are undergoing? Develop a hypothesis that might explain what you see.
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2. Cell Cycle: The regular sequence of growth and division that cells undergo.
The Cell Cycle is divided into three main stages: interphase, mitosis, and cytoknesis.

3. Preparing for Division
STAGE 1: INTERPHASE
During interphase, the cell grows, makes a copy of its DNA, and prepares to divide into two cells.
Growing
Copying DNA
Preparing for Division
Cell grows to full size and produces structures.
Cell makes exact copy of DNA in its nucleus.
Cell produces structures that it will use to divide into two new cells.

4. STAGE 2: MITOSIS
During mitosis, one copy of the DNA is distributed into each of the two daughter cells.
Prophase
The threadlike chromatin in the nucleus condenses to form double-rod structures called chromosomes.
Metaphase
The duplicated chromosomes become aligned in the center of the cell.
Anaphase
Duplicated sets of chromosomes separate and two identical groups move to opposite poles of the cell.
Telophase
A nuclear membrane is formed around each new group of chromosomes.

5. Identify each step of Mitosis.
STAGE 2: MITOSIS
Identify each step of Mitosis.
1. Prophase
2. Metaphase
3. Anaphase
4. Telaphase

6. STAGE 3: CYTOKINESIS
During cytokinesis, the cytoplasm divides. The organelles are distributed into each of the two new cells.
Cytokinesis in Animal Cells
Cytokinesis in Plant Cells
Cell membrane squeezes together, pinching into two cells.
Organelles are evenly shared.
Cell plate forms across the middle of the cell.
Cell plate gradually develops into new cell membranes between the daughter cells.

7. Structure and Replication of DNA
DNA replication ensures that each daughter cell will have the genetic information it needs to carry out its activities.
The Structure of DNA
The Replication Process
The DNA molecule is shaped like a twisted ladder.
Each side of the ladder is made of sugars (deoxyribose) and phosphates.
The rungs are made of pairs of nitrogen bases: adenine (A), thymine (T), guanine (G), and cytosine (C).
Replication occurs when the two sides of DNA molecules unwind and separate into two bases.
New bases pair with the bases on each old strand.
As a result two identical DNA strands form.

8. Section 3-5 Assessment
1.a. What are the three stages of the cell cycle?
Summarize what happens to chromosomes during the stage of the cell cycle in which the nucleus divides. Include the terms prophase, metaphase, anaphase, and telophase.
Look at Figure 21. What is the role of spindle fibers during cell division?
2.a. List the nitrogen bases in DNA.
Describe how the nitrogen bases pair in a DNA molecule.
One section of a strand of DNA has the base sequence AGATTC. What is the base sequence on the other strand?