Download The Cell Cycle

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
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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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ANIMATION