Chapter 4:3 - The Cell Cycle

Chapter 4:3

The Cell Cycle

By: Ms. Della D.

@Della802

Chapter 4 - Section 3

The Cell Cycle

Pages 98-101

The Life of a Cell

Page 98

The Cell Cycle

• The life cycle of a cell is called the cell cycle.

• It begins when the cell is formed and ends when the cell divides and forms new cells.

DNA

• DNA stands for deoxyribonucleic acid.

• Before a cell divides, it must make a copy of its DNA.

• DNA is the hereditary material that controls all cell activities, including the making of new cells.

Chromosomes

• The DNA of a cell is organized into structures called chromosomes.

• Copying chromosomes ensures that each new cell will be an exact copy of its parent cell.

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How Does A Cell Make More Cells?

• It depends on whether the cell is prokaryotic or eukaryotic.

• Prokaryotic cells do NOT have a nucleus.

• Eukaryotic cells do have a nucleus.

Making More Prokaryotic Cells

Page 98

Prokaryotic Cells

• Prokaryotic cells do not have a nucleus.

• Prokaryotic cells are less complex than eukaryotic cells are.

Bacteria

• Bacteria are prokaryotes.

• They have ribosomes and a single, circular DNA molecule.

• They do NOT have membrane-enclosed organelles.

Binary Fission

• Cell division in bacteria is called bacteria fission.

• Binary fission means "splitting into two parts."

• Binary fission results in two cells that each contain one copy of the circle of DNA.

A few of the bacteria in Figure 1 are undergoing binary fission.

Eukaryotic Cells and Their DNA

Page 99

Eukaryotic Cells

• Eukaryotic cells have a nucleus.

• Eukaryotic cells are more complex than prokaryotic cells are.

Eukaryotic Cells & Chromosomes

• The chromosomes of eukaryotic cells contain more DNA than those of prokaryotic cells do.

• Different kinds of eukaryotes have different numbers of chromosomes.

• More-complex eukaryotes do not necessarily have more chromosomes than simpler eukaryotes do.

Examples

• Fruit flies have 8 chromosomes.

• Potatoes have 48 chromosomes.

• Humans have 46 chromosomes.

Figure 2

• Figure 2 shows the 46 chromosomes of a human body cell lined up in pairs.

• These pairs are made up of similar chromosomes known as homologous chromosomes.

Making More Eukaryotic Cells

Page 99

The Eukaryotic Cell Cycle

• The eukaryotic cell cycle includes three stages.

Stage 1 - Interphase

• In the first stage, called interphase, the cell grows and copies its organelles and chromosomes.

• After each chromosomes is duplicated, the cell enters the second stage of the cell cycle.

Stage 2

• In the second stage, each chromosome twists, coils, and condenses into an X shape.

• The X shape is made up of two chromatids, which are held together at a region called the centromere.

• After this step, the chromatids separate.

Figure 3

• As shown in Figure 3, the chromosome twists, coils, and condenses into an X shape during the second stage.

• The duplicated chromosome consists of two chromatids.

• The chromatids are joined at the centromere.

Stage 2 (Continued)

• The complicated process by which chromosomes condense and separate is called mitosis.

• Mitosis ensures that each new cell receives a copy of each chromosome.

• Mitosis is divided into four phases.

Stage 3

• In the third stage, the cell splits into two cells.

• These cells are identical to each other and to the original cell.

Mitosis and the Cell Cycle

Page 100

Figure 4

• Figure 4 is shown on the next two slides.

• Figure 4 shows the cell cycle and the phases of mitosis in an animal cell.

• Mitosis has four phases that are shown and described in Figure 4.

• The diagram shows only four chromosomes to make it easy to see what is happening inside the cell.

Cytokinesis

Page 100

Cytokinesis: The Division of a Cytoplasm

• In animal cells and other eukaryotes that do not have cell walls, division of the cytoplasm begins at the cell membrane.

• The cell membrane begins to pinch inward to form a groove, which eventually pinches all the way through the cell, and two daughter cells form.

• The division of the cytoplasm is called cytokinesis and is shown at the last step of Figure 4.

Cytokinesis & Cell Plates

• Eukaryotic cells that have a cell wall, such as the cells of plants, algae, and fungi, reproduce differently.

• In these cells, a cell plate forms in the middle of the cell.

• The cell plate contains the materials for the new cell membranes and the new cell walls that will separate the new cells.

• After the cell splits into two, a new cell forms where the cell plate was.

Figure 5

• The cell plate and a late stage of cytokinesis in a plant cell are shown in Figure 5.

• When a plant cell divides, a cell plate forms and the cell splits into two cells.

Section Summary & Vocabulary

Page 101

Summary:

• A cell produces more cells by first copying its DNA.

• Eukaryotic cells produce more cells through the four phases of mitosis.

• Mitosis produces two cells that have the same number of chromosomes as the parent cell.

• At the end of mitosis, a cell divides the cytoplasm by cytokinesis.

• In plant cells, a cell plate forms between the two new cells during cytokinesis.

Cell Cycle

The cell cycle is the life cycle of a cell.

Chromosome

In a eukaryotic cell, a chromosome is one of the structures in the nucleus that are made up of DNA and protein.

In a prokaryotic cell, a chromosome is the main ring of DNA.

Homologous Chromosome

Chromosomes hat have the same sequence of genes and the same structure.

Mitosis

In eukaryotic cells, mitosis is a process of cell division that forms two new nuclei, each of which has the same number of chromosomes.

Cytokinesis

Cytokinesis is the division of the cytoplasm of a cell.

Section Review Quiz

Answer the following questions. Give the best answer you can!

Open Ended

In your own words, write a definition for each of the following terms:

cell cycle and cytokinesis.

Answer:

Answers may differ but they must be along the lines of:

(1) The cell cycle is the life cycle of a cell.

(2) Cytokinesis is teh division of the cytoplasm of a cell.

Multiple Choice

Which of the following would best fill in the blank?

Eukaryotic cells ______.

• do not divide.

• undergo binary fission.

• undergo mitosis.

• have cell walls.