The cell cycle (ingles)

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Chapter 11

The Cell Cycle

Biological Science, Third Edition
– Scott Freeman
Lectures by Cheryl Ingram-Smith
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings/Addison-Wesley

Key Concepts
• After chromosomes are copied, mitosis distributes one chromosome copy to each of two daughter cells. Mitosis and cytokinesis produce two cells that are identical tothe parent cell. • Over their life span, eukaryotic cells go through a cycle that consists of four carefully controlled phases. • In multicellular organisms, uncontrolled cell growth leads to cancer. Different types of cancer result from different types of defects in control over the cell cycle.

Introduction: Meiosis
• Cells arise through the division of preexisting cells. There are two typesof cell division: meiosis and mitosis. • Meiosis is a division of the genetic material in the nucleus to produce daughter cells with one-half the amount of hereditary material found in the parent cell. Meiosis is involved only in the production of gametes (eggs and sperm); it is the basis of sexual reproduction and genetic inheritance (see Chapter 12).

Copyright © 2008 Pearson Education Inc.,publishing as Pearson Benjamin Cummings/Addison-Wesley

Introduction: Mitosis
• Mitosis is a division of the genetic material in the nucleus that produces daughter cells genetically identical to the parent cell. • Mitosis is usually accompanied by cytokinesis, the division of the cytoplasm into the two daughter cells. • Mitosis is the basis of asexual reproduction and is involved only in theproduction of somatic (body) cells. It is responsible for three key events in multicellular eukaryotes: (1) growth, (2) wound repair, and (3) cellular reproduction.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings/Addison-Wesley

Two Types of Nuclear Division Occur in Many Species

MEIOSIS

Amount of hereditary material is reduced by half

In animals,meiosis occurs prior to production of eggs and sperm Gametes Egg Sperm

Cell divisions responsible for growth (addition of somatic cells)

Fertilized egg

Normal amount of hereditary material is restored

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings/Addison-Wesley

Mitosis and the Cell Cycle
• Chromosomes contain a long double helix of deoxyribonucleicacid (DNA) wrapped around proteins. DNA carries the cell’s genetic information. The purpose of mitosis is to distribute this genetic material to daughter cells during cell division. • Chromosomes can be stained with dyes and observed under the light microscope. • Prior to mitosis, each chromosome is duplicated. As mitosis starts, the chromosomes condense from long, thin filaments into compactstructures that can be moved around the cell efficiently.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings/Addison-Wesley

Chromosomes Can Be Observed in the Light Microscope

…now understood to be chromosomes

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings/Addison-Wesley

Chromosome Morphology and Mitosis
Unreplicatedchromosome
The unreplicated chromosome consists of a single, long strand of DNA wrapped around proteins (proteins not shown).

Gene 1

Gene 2

The DNA replicates, resulting in two copies of the same chromosome..

Replicated chromosome
Copies of same chromosome

Gene 1 Gene 1

Gene 2 Gene 2 The DNA condenses around its associated proteins, resulting in a compact chromosome that is 10,000times shorter than its original length.

Condensed replicated chromosome
Copies of same chromosome, condensed Centromere

Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings/Addison-Wesley

Chromosome Morphology and Mitosis
Unreplicated chromosome
The unreplicated chromosome consists of a single, long strand of DNA wrapped around proteins (proteins not...
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