1. Chapter 9 Lecture Outline See PowerPoint Image Slides
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2. The Importance of Cell Division
The ability to grow and reproduce are two fundamental qualities of life.
During cell division, one cell becomes two new cells.
Accomplishes growth and reproduction
Reproduction occurs as binary fission in prokaryotes.
Growth and some reproduction occurs as mitosis in eukaryotes.
Reproduction often involves meiosis in eukaryotes.
All cell division is preceded by DNA replication.
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3. Uses of Binary Fission and Mitosis
In single-celled organisms
Mitosis and binary fission are means of asexual reproduction.
In multi-cellular organisms mitosis:
Causes growth by increasing the number of cells
Replaces lost cells
Repairs injuries
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4. Uses of Meiosis
Sexual reproduction involves the donation of genetic information from two parents.
Each parent can only donate half of the genome.
Meiosis occurs prior to sexual reproduction.
Generates gametes (egg and sperm) with half of a genome
The egg and sperm then join during fertilization to make a unique offspring with a full complement of genetic information.
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5. The Cell Cycle Eukaryotic cells
Pass through different stages between the time they are “born” and the time they divide again
A continuous process
Includes interphase and mitosis
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6. Interphase-G1 During interphase, cells The three phases of interphase
Engage in metabolic activities
Prepare for the next cell division
The three phases of interphase G1
The cell gathers nutrients, carries out its regular metabolic roles, and performs its normal function.
Commits to divide
Some cells never divide; they stay in G1, called Go..
Prepares for DNA replications
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7. Interphase-S S phase DNA replication occurs.
The DNA in chromosomes is wrapped around histones.
DNA + histones = chromatin
When S phase is complete
The identical copies are connected together.
Each is called a sister chromatid.
Connected at the centromere
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8. Interphase-G2 During G2 Final preparations are made for mitosis.
Proteins are made that will move and separate the chromosomes.
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9. Mitosis-Cell Replication
The two events of cell division
Mitosis
Separating the chromosome copies into two new nuclei
Occurs in four phases that are continuous with one another
Cytokinesis
Dividing the cytoplasm into two new cells that will house the new nuclei
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10. Prophase The thin, tangled chromatin gradually coils and thickens.
Becomes visible as separate chromosomes, each with two sister chromatids
Nucleus disassembles.
Nucleolus is no longer visible.
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11. Late Prophase
Spindle fibers attach to chromosomes at their centromeres.
Spindles are made of microtubules.
In animals, they form from the centrioles.
Asters form only in animal cells.
Will move chromosomes around.
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12. Metaphase
The spindle fibers move the chromosomes so that they are all arranged at the middle of the cell.
This is called the equatorial plate.
Chromosomes complete this process at metaphase.
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13. Metaphase
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14. Anaphase Sister chromatids separate and move toward opposite poles.
Once the sister chromatids are separated, they are known as daughter chromosomes.
What moves the sister chromatids to opposite poles?
The poles begin to move farther apart.
The kinetochore (proteins attached at the centromere) pulls the chromatid along the spindle fiber.
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15. Kinetochores
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16. Anaphase
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17. Telophase Spindle fibers disassemble.
Nuclear membranes form around the two new sets of chromosomes.
Chromatin uncoils.
Nucleolus reforms.
The daughter cells enter interphase again.
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18. Cytokinesis Separates the two new nuclei into new cells
Roughly divides the cytoplasm and its contents in half
Animal cells
Membrane forms a cleavage furrow
Cell pinches into two
Plant cells
Cell plate is formed.
A new cell wall is built, separating the nuclei.
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19. Controlling Cell Division
Cells gather information about themselves and their environment in order to decide whether or not to divide.
A cell decides whether to proceed through the cell cycle at checkpoints.
Cells evaluate their genetic health, their location in the body and the body’s need for more cells.
Poor genetic health, wrong location in the body or over-crowding will cause the cell to wait before dividing.
The opposite signals will trigger the cell to proceed with division.
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20. Genes Regulate the Cell Cycle
Cells use several proteins to function as checkpoints.
These proteins make the decision to proceed through the cell cycle or to stop.
Two classes of genes that code for checkpoint proteins
Proto-oncogenes
Code for proteins that encourage cell division
Tumor-suppressor genes
Code for proteins that discourage cell division
The balance of these two types of proteins tells the cell whether or not to proceed with cell division.
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