Cell Division and Mitosis

Chapter 10

10.1 The Cycle of Cell Growth and Division: An Overview

The products of mitosis are genetic duplicates of the dividing cell

Chromosomes are the genetic units divided by mitosis

Mitotic Cell Division

DNA replication

Equal separation (segregation) of replicated DNA molecules

Delivery to daughter cells• Two new cells, same information as parent cell

Mitosis

Mitosis is the basis for• Growth and maintenance of body mass in

multicelled eukaryotes

• Reproduction of many single-celled eukaryotes

Chromosomes

DNA of eukaryotic cells is divided among individual, linear chromosomes • Located in cell nucleus

Ploidy of a cell or species• Diploid (2n)

• Haploid (n)

Eukaryotic Chromosomes

Fig. 10-2, p. 203

Sister Chromatids

DNA replication and duplication of chromosomal proteins produces two exact copies (sister chromatids)

Chromosome segregation occurs during cell division

10.2 The Mitotic Cell Cycle

Interphase extends from the end of one mitosis to the beginning of the next mitosis

After interphase, mitosis proceeds in five stages

Cytokinesis completes cell division by dividing the cytoplasm between daughter cells

10.2 (cont.)

The mitotic cell cycle is significant for both development and reproduction

Mitosis varies in detail, but always produces duplicate nuclei

Mitotic Cell Cycle

Includes mitosis and interphase

Mitosis occurs in five stages• Prophase

• Prometaphase

• Metaphase

• Anaphase

• Telophase

The Cell Cycle

Fig. 10-3, p. 203

Interphase

Fig. 10-4a (1), p. 204

Fig. 10-4b, p. 205

Stage 1: Prophase

Chromosomes condense into short rods

Spindle forms in the cytoplasm

Prophase

Fig. 10-4a (2), p. 204

Stage 2: Prometaphase

Nuclear envelope breaks down• Spindle enters former nuclear area

• Sister chromatids of each chromosome connect to opposite spindle poles

Kinetochore of each chromatid attaches to the spindle microtubules

Prometaphase

Fig. 10-4a, p. 204

Spindle Connections at Prometaphase

Fig. 10-6, p. 206

Stage 3: Metaphase

Spindle is fully formed

Chromosomes align at metaphase plate• Moved by spindle microtubules

Metaphase

Fig. 10-4b, p. 204

Stage 4: Anaphase

Spindle separates sister chromatids and moves them to opposite spindle poles

Chromosome segregation is complete

Anaphase

Fig. 10-4b, p. 204

Stage 5: Telophase

Chromosomes decondense• Return to extended state typical of interphase

New nuclear envelope forms around chromosomes

Telophase

Fig. 10-4b, p. 204

Animation: Mitosis step-by-step

Mitosis

Fig. 10-5, p. 206

Cytokinesis

Division of cytoplasm completes cell division

Produces two daughter cells• Each daughter nucleus produced by mitosis

Cytokinesis in Animal Cells

Proceeds by furrowing• Band of microfilaments just under the plasma

membrane contracts

• Gradually separates cytoplasm into two parts

Cytokinesis by Furrowing

Fig. 10-8, p. 208

Plant Cytokinesis

Cell wall material is deposited along the plane of the former spindle midpoint

Deposition continues until a continuous new wall (cell plate) separates daughter cells

Cytokinesis by Cell Plate Formation

Fig. 10-9, p. 208

10.3 Formation and Action of the Mitotic Spindle

Animals and plants form spindles in different ways

Mitotic spindles move chromosomes by a combination of two mechanisms

Spindle Formation

In animal cells• Centrosome divides, the two parts move apart

• Microtubules of the spindle form between them

In plant cells with no centrosome• Spindle microtubules assemble around the nucleus

Centrosome and Spindle Formation

Fig. 10-10, p. 210

In the Spindle

Kinetochore microtubules • Run from poles to kinetochores of chromosomes

Nonkinetochore microtubules • Run from poles to a zone of overlap at the

spindle midpoint without connecting to chromosomes

A Fully Developed Spindle

Fig. 10-11, p. 210

During Anaphase

Kinetochores move along kinetochore microtubules• Pulling chromosomes to the poles

Nonkinetochore microtubules slide over each other • Pushing the poles farther apart

Anaphase Spindle Movements

Fig. 10-12, p. 211

Kinetochore Movement

Fig. 10-13, p. 211

10.4 Cell Cycle Regulation

Cyclins and cyclin-dependent kinases• Internal controls that directly regulate cell division

Internal checkpoints• Stop cell cycle if stages are incomplete

External controls• Coordinate mitotic cell cycle of individual cells

within overall activities of the organism

Cell Cycle Control (1)

Complexes of cyclin and a cyclin-dependent protein kinase (CDK) • Directly control cell cycle

CDK • Is activated when combined with a cyclin

• Adds phosphate groups to target proteins, activating them

Cell Cycle Control (2)

Activated proteins trigger the cell to progress to the next cell cycle stage

Each major stage of the cell cycle• Begins with activation of one or more cyclin/CDK

complexes

• Ends with deactivation of complexes by breakdown of cyclins

Cyclin/CDK Control

Fig. 10-15, p. 214

Internal Controls

Important internal controls create checkpoints• Ensure that the reactions of one stage are

complete before cycle proceeds to next stage

External Controls

Based on surface receptors that recognize and bind signals • Peptide hormones and growth factors

• Surface groups on other cells

• Molecules of the extracellular matrix

Binding triggers internal reactions that speed, slow, or stop cell division

Cancer

Control of cell division is lost • Cells divide continuously and uncontrollably

• Form rapidly growing mass of cells that interferes with body functions

Cancer cells break loose from their original tumor (metastasize)• Form additional tumors in other parts of the body

Tumor Cells

Fig. 10-16, p. 215

Animation: Mitosis overview

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