Mitosis

Mitosis

Middle School

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Learning Objectives

• Describe the main stages of the eukaryotic cell cycle.

• Identify the four phases of mitosis and describe the key events in each.

• Explain the difference between mitosis and cytokinesis.

• Understand the outcome of mitosis in producing two identical daughter cells.

Key Vocabulary

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Mitosis

The process of cell division that results in two identical daughter cells from a single parent cell.

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Chromosome

A coiled structure of DNA and protein that forms in the nucleus during cell division.

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Centromere

The region of a chromosome where the two sister chromatids are joined tightly together.

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Cytokinesis

The final stage where the cytoplasm divides, forming two separate and distinct daughter cells.

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Interphase

The phase between divisions where the cell grows, functions, and copies its DNA before mitosis begins.

The Eukaryotic Cell Cycle

• The cell cycle has two main parts: interphase and the mitotic phase.

• Interphase involves cell growth, DNA replication, and preparation for division.

• The mitotic phase includes the division of the nucleus and the cytoplasm.

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• The cell cycle has two main parts: interphase and the mitotic phase.

• Interphase involves cell growth, DNA replication, and preparation for division.

• The mitotic phase includes the division of the nucleus and the cytoplasm.

Multiple Choice

During which phase of the cell cycle is the cell’s DNA synthesized?

• G1 phase

• S phase

• G2 phase

• Mitotic phase

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DNA and Chromosomes

• In non-dividing cells, DNA exists in a less condensed form called chromatin.

• Chromatin is made of DNA strands wrapped around special proteins called histones.

• Before a cell divides, chromatin coils tightly to form a chromosome.

• Chromosomes are made of two identical copies called sister chromatids.

Multiple Choice

What are the two identical copies of a replicated chromosome called?

• Chromatin

• Histones

• Sister chromatids

• Centromeres

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Mitosis: Prophase and Metaphase

Prophase

• Chromatin condenses and becomes visible as distinct chromosomes.

• The nuclear membrane breaks down, and centrioles move to opposite sides of the cell.

• Spindle fibers begin to form, creating a framework for the chromosomes' movement.

Metaphase

• Chromosomes, each consisting of two sister chromatids, line up at the cell’s center.

• This imaginary line where the chromosomes align is called the metaphase plate.

• Spindle fibers attach to the centromere of each of the individual chromosomes.

Multiple Choice

What happens to the chromosomes during metaphase?

• They condense and become visible.

• They line up at the center of the cell.

• They separate and move to opposite poles.

• They uncoil back into chromatin.

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Mitosis: Anaphase and Telophase

Anaphase

• Spindle fibers shorten, pulling the sister chromatids apart to opposite poles of the cell.

• Each chromatid is now considered an individual chromosome.

• Each pole of the cell now has a complete and identical set of chromosomes.

Telophase

• Chromosomes arrive at the poles and uncoil to form chromatin.

• A new nuclear membrane forms around each set of chromosomes.

• The spindle fibers break down, and mitosis is complete.

Multiple Choice

During which phase do the sister chromatids separate and move to opposite poles of the cell?

• Prophase

• Metaphase

• Anaphase

• Telophase

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Cytokinesis: Splitting the Cytoplasm

Animal Cells

• A cleavage furrow forms as the cell membrane starts to pinch inward.

• The furrow deepens until the cytoplasm is pinched in half.

• This process results in the formation of two separate daughter cells.

Plant Cells

• A structure called the cell plate forms in the middle of the cell.

• This plate grows outward to join the existing cell wall.

• A new cell wall and membrane form, separating the two daughter cells.

Multiple Choice

How does cytokinesis differ in plant cells compared to animal cells?

• A cleavage furrow pinches the cell in half.

• The cytoplasm is not divided.

• A cell plate forms in the middle of the cell.

• It happens before mitosis.

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Common Misconceptions

Misconception	Correction
Interphase is a 'resting' phase.	It's an active period of growth, DNA replication, and protein production.
Mitosis is the same as cell division.	Mitosis is nucleus division; cell division includes mitosis and cytokinesis.
An organism grows as its cells get bigger.	Growth is due to producing more cells, not larger individual cells.

Multiple Choice

A cell has its nuclear membrane dissolved and its chromosomes condensed and visible. Why is it not possible for the cell to be in anaphase?

• Because in anaphase, the nuclear membrane is reforming.

• Because in anaphase, the chromosomes are lined up in the middle.

• Because in anaphase, the sister chromatids have already been pulled apart.

• Because in anaphase, the cell is still in interphase.

Multiple Choice

How does the structure of a chromosome in prophase differ from the structure of a chromosome in telophase?

• In prophase it is uncoiled chromatin, while in telophase it is a condensed X-shape.

• In prophase it is a condensed X-shape, while in telophase it is uncoiling into chromatin.

• There is no difference in their structure.

• In prophase it is a single chromatid, while in telophase it is two sister chromatids.

Multiple Choice

If a parent cell has 46 chromosomes, what is the expected outcome after it undergoes one complete cycle of mitosis and cytokinesis?

• One daughter cell with 23 chromosomes.

• Two daughter cells, each with 23 chromosomes.

• Four daughter cells, each with 46 chromosomes.

• Two daughter cells, each with 46 chromosomes.

Multiple Choice

Predict what might happen if the spindle fibers failed to form properly during mitosis.

• The nuclear membrane would not dissolve.

• The DNA would not replicate.

• The chromosomes would not be able to separate and move to opposite poles.

• The cytoplasm would not be able to divide.

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Summary

• The cell cycle includes interphase for growth and the mitotic phase for division.

• DNA condenses into chromosomes, and the nuclear membrane dissolves during prophase.

• Chromosomes align at the cell's center in metaphase and separate during anaphase.

• New nuclei form in telophase, and cytokinesis divides the cell into two.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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