Module 5 Lesson 2 - 3

• Lesson 2 - Mitosis
  

Images of Lily Cells

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Here are some light microscope images of African globe lily cells undergoing mitosis. The chromosomes of lily cells are much larger than human chromosomes and can be viewed easily under a light microscope. The chromosomes are stained dark blue and the spindle fibres (microtubules) are stained red.

All images are from the NIGMS Image and Video Gallery and are in the public domain.

Associating the terms you are learning with the correct images represented in diagrams and/or flow charts of the processes is vital to this lesson.

Plant and Animal Cells

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Consider the two sets of slide images below. How are they similar? How are they different?


If you have good observation skills, you should notice two clear differences between animal (left) mitosis and plant (right) mitosis. First, plant cell walls are rigid and cannot go through cleavage. Instead, a new cell wall is formed between the daughter cells called a cell plate. Second, plant cells do not have centrioles. They form a spindle apparatus to move chromosomes around, but they must anchor this apparatus to the cell wall instead of to the centrioles as animal cells do.

Controlling the Cell Cycle

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The checkpoints within the cell regulate division. These are of great interest when considering how cells ensure that they are growing and are themselves capable of division. The cell cycle has three major checkpoints.

1. The end of G1: Here, the cell evaluates if it is large enough and strong enough to continue with the division process.


2. The end of G2: This is a very important checkpoint for the cell. At this time, the cell must evaluate if it has properly duplicated all its chromosomes. If it has not, it may attempt to carry on with the division, or it may self-destruct.


3. During M phase: At this checkpoint, the cell evaluates whether the spindle apparatus has attached itself properly to each of the chromosomes and whether the remainder of the cell is ready for cytokinesis, or physical cell division. If something is wrong at this stage, the cell usually dies.

Try This

• Having learned the major divisions of the cell cycle, consider the following animation which brings each stage of the cell cycle together and illustrates how they typically work in a eukaryotic cell. The animation also introduces you to three key check points of the cell cycle. While you watch, consider why these checkpoints are important and why they occur when they do. 

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Watch and Listen

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You should now have functional knowledge of each phase of mitosis. Review how the phases work together by watching the following animation and video. 

Give attention to key events and structures of each phase. What happens to the nuclear membrane before, during, and after mitosis? What roles or actions do the spindle fibres fulfill? How do the chromosomes line up along the equatorial plate?

Note: This animation refers to the kinetochore, a protein structure located on the centromere. The spindle fibres attach to the kinetochore when pulling the sister chromatids apart. You do not need to know this terminology for this course.