This lab has one submission form off BlackBoard. Please submit your answers by Wednesday, 4/10/01, at midnight.

Learning Objectives:

Understand the process of eukaryotic cell division.
Gain familiarity with the stages of mitosis.
Be able to recognize the stages of mitosis in stained preparations of cells and in models.

Introduction:

Cell division is a necessary process for all organisms. It allows unicellular organisms to reproduce, and it enables repair and growth in multicellular organisms. In this lab we will be exploring cell division in eukaryotic cells only.

Figure 1: DNA in its different forms and views.

Part A Part A is a cartoon of a DNA molecule at its atomic level; we cannot see DNA in this detail using a microscope. Part B of this figure is a photograph of a dividing cell. Chromosomes are apparent as dark structures within this plant cell. If you could take out all of the chromosomes of one human cell and look at them at a higher magnification, you would see something like in the last part (part D) of this figure. Part C of this figure shows a purplish cell (a neuron) and its nucleus appears very light. This neuron is not dividing, so its DNA is in the form of chromatin, visible as the spotty material within the nucleus; the dark dot is the nucleolus. The neuron's cytoplasm appears very purple in this stained cell. Part D shows chromosomes as they would look if you could spill them all out of a cell. All of the chromosomes in Part D would be found within one nucleus when a human cell divides.

Many cells live, then divide, then live, then divide, over and over. This cycle of regular living and dividing has been called the cell cycle. The cell cycle has two main parts:

	interphase—when the cell is doing its regular living; it may engage in activities such as moving, ingesting nutrients, expelling wastes, and communicating with other cells during interphase. It may also prepare for cell division by increasing in size, increasing its number of organelles, and copying its DNA during interphase.
	mitosis & cytokinesis—when the cell is dividing.

	mitosis is when the nucleus divides, providing a full complement of genetic material to each daughter cell.
	Cytokinesis is when the cell itself is split in two, dividing the cytoplasm up into two separate cells.

We are going to focus on mitosis in this lab. In order to understand mitosis, one must first understand the structure of the DNA within a nucleus. During most of the life of a cell, the DNA within the nucleus is loosely folded with proteins. This loosely folded form of DNA is called chromatin. However, in order for a cell to reproduce, it must first tightly pack up its DNA with proteins. This tightly-packed form of DNA is called a chromosome. You can see both of these version of DNA in Figure 1.

During interphase, as a cell prepares for cell division, the cell’s DNA is copied; that way it has enough DNA to give to each of the two daughter cells. Therefore, when DNA condenses into a chromosome as a cell begins to divide, each chromosome is made up of two identical molecules of DNA, referred to as sister chromatids. These sister chromatids are held together at a region called the centromere. Since each daughter cell will only need one copy of the genetic information, during division the sister chromatids separate... Each chromatid becomes a chromosome in its daughter cell.

Figure 2: Sister Chromatids and Daughter Chromosomes

Note that if you look back at Figure 1D, you will see that each of the chromosomes actually looks like the drawing at the left of Figure 2 (each chromosome has sister chromatids).

Finally, you may be able to see how plant cells manage to perform cytokinesis while you are viewing your cells. If you look closely at cells late in cell division, you may begin to see the cell plate, which is how plant cells do cytokinesis.

This animation is copywritten by Rafael Tormo Molina and is being used after asking for permission. Here's a little animation that I have "borrowed" from a plant mitosis web site. I thought that it might be helpful as you try to understand what goes on during mitosis in plant cells.

© 2006 STCC Foundation Press, content by Dawn A. Tamarkin, Ph.D.

Last changed: January 21, 2007

Learning Objectives:

Table of Contents:

Introduction (this page)

Exercises:

Appendices

Introduction:

Last changed: January 21, 2007