Mader: Biology 8th Ed.

The Cell Cycle and Cellular Reproduction

Chapter 9

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Mader: Biology 8th Ed.

Outline

• Interphase

• Mitotic Stage

• Cell Cycle Control

• Apoptosis

• Mitosis

• Mitosis in Animal Cells

• Cytokinesis

• Cancer

• Prokaryotic Cell Division

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Interphase

• Most of the cell cycle is spent in interphase.

– G1 - Cell doubles its organelles and

accumulates materials needed for DNA synthesis.

– S - DNA replication.

– G2 - Cell synthesizes proteins necessary

for cell division.

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Mitotic Stage

• Cell division stage that includes mitosis (nuclear division) and cytokinesis (cytoplasm division).

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Cell Cycle

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Cell Cycle Control

• Researchers have identified internal signal protein (cyclin) that increases and decreases as cell cycle continues.

– Must be present for the cell to proceed from the G2 stage to the M stage and

from G1 stage to S stage.

!Allows time for any damage to be repaired.

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Cell Cycle Control

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Apoptosis

• Often defined as programmed cell death.

– Cells routinely harbor enzymes (caspases) necessary for apoptosis to occur.

!Ordinarily held in check by inhibitors, but can be unleashed by internal or external signals.

• Mitosis increases and apoptosis decreases the number of somatic cells.

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Apoptosis

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Fig. 9A

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Mitosis

• When a eukaryotic cell is not undergoing division, the DNA within the nucleus is a tangled mass of chromatin.

– Condenses into chromosomes

!Each species has a characteristic number of chromosomes.

"Diploid (2n) - Two of each kind.

"Haploid (1n) - One of each kind.

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Mitosis

• During mitosis, a diploid nucleus divides to produce diploid daughter nuclei.– Two identical chromatids are called sister

chromatids.!Attached to each other at centromere.

"During nuclear division, sister chromatids separate at the centromeres, and each duplicated chromosome gives rise to two daughter chromosomes.

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Duplicated Chromosomes

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Mitosis in Animal Cells

• Each centromere in an animal cell contains a pair of barrel-shaped organelles (centrioles) and an array of short microtubules (aster).

– Centromeres organize mitotic spindle, which contains many fibers, each composed of a microtubule bundle.

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Mitosis in Animal Cells

• Prophase

– Chromatin has condensed.

– Nucleolus disappears.

– Nuclear envelope disintegrates.

– Spindle begins to assemble.

• Prometaphase

– Kinetochores develop on centromere.

!Attach sister chromatids to spindle fibers.

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Fig. 9.4p154d

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Fig. 9.4p154e

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Fig. 9.4p154f

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Mitosis in Animal Cells

• Metaphase

– Chromosomes, attached to kinetochore fibers, are in alignment at center of cell.

• Anaphase

– Sister chromatids split, producing daughter chromosomes.

!Daughter chromosomes are pulled to opposite poles.

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Mitosis in Animal Cells

• Telophase

– Spindle disappears as new nuclear envelopes form around the daughter chromosomes.

!Chromosomes become diffuse chromatin again.

!Nucleolus appears in each daughter nucleus.

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Fig. 9.4p155d

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Fig. 9.4p155e

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Fig. 9.4p155f

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Plant Cell Division

• Meristematic plant tissue retains the ability to divide throughout the plant’s life.

– Found at root and shoot tips.

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Phases of Mitosis in Plant Cells

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Cytokinesis

• Cytokinesis accompanies mitosis in most cells, but not all.

– Mitosis without cytokinesis results in a multinucleated cell.

!Begins in anaphase, continues in telophase, but does not reach completion until the following interphase begins.

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Cytokinesis

• Animal Cells

– Cleavage furrow, membrane indentation between daughter nuclei, begins as anaphase nears completion.

!Deepens when a band of actin filaments (contractile ring) forms a circular constriction between the two daughter cells.

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Cytokinesis in Animal Cells

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Cytokinesis

• Plant Cells

– Rigid cell wall surrounding plant cells does not permit cytokinesis by furrowing.

!Begins with formation of a cell plate which eventually becomes new plasma membrane between the daughter cells.

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Cytokinesis in Plant Cells

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Prokaryotic Cell Division

• Asexual Reproduction - offspring are genetically identical to the parent.

– Binary fission produces two (binary) daughter cells that are identical to the original parent.

!Prokaryotes contain a single chromosome with only a few proteins.

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Binary Fission

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Review

• Interphase

• Mitotic Stage

• Cell Cycle Control

• Apoptosis

• Mitosis

• Mitosis in Animal Cells

• Cytokinesis

• Cancer

• Prokaryotic Cell Division

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