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Chapter 9 Cell Division and Mitosis PowerPoint PPT Presentation

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Chapter 9 Cell Division and Mitosis. Why do Cells divide?. Growth Reproduction (for single cell organisms) Repair. Cycle of Life.

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Chapter 9 Cell Division and Mitosis

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Chapter 9 cell division and mitosis l.jpg

Chapter 9Cell Division and Mitosis

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Why do Cells divide?

  • Growth

  • Reproduction (for single cell organisms)

  • Repair

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Cycle of Life

  • The cycle of life includes fertilization of gametes, cell division, and growth, production of gametes, and death.

  • All of life depends of life

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Overview of Division mechanisms

  • Before a cells are able to reproduce, there must be a division of nucleus and its DNA

  • Mitosis: used by multicellular organisms for growth by repeated division of somatic (body cells)

    • This division helps cells grow, replace dead, or worn-out cells and repair tissues

  • Meiosis: only occurs in germ cells that divide to form gametes (sex cells)

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  • Each chromosomes is a molecule of DNA complexed with proteins

  • Human DNA is 2 meters long

    • Prior to cell division, each threadlike chromosomes is duplicated to form two sister chromatids held together by a centromere

    • The centromere is also the region where the duplicated chromosome will attach to the microtubules of the spindle during nuclear division

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  • Proteins called histones tightly bind to DNA and cause spooling into a structural unit called nucleosome

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Mitosis and Chromosome Number

  • Each organisms has a definite chromosome number

    • Example: Humans have 46 chromosomes

  • Chromosomes exists in pairs (one from each parent)

    • Humans have 23 pairs of chromosomes

    • Somatic Cells are diploid (pairs)

    • Germ cells (sperm and egg cells) are haploid (half the number of total chromosomes)

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Cell Cycle

  • A recurring sequence of events that extends from the time of a cell’s formation until each division is complete

    • Three phases of cell cycle: Interphase, Mitosis , and Cytokinesis

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  • Is the portion of the cell cycle is which the cell prepares for cell division (nuclear and cytoplasmic)

  • Three phases of Interphase

    • G1 phase: Carbohydrates, lipids, and proteins for cell’s own use and for export assembled

    • S phase: DNA is copied and proteins are synthesized used in organizing the condensed chromosomes

    • G2 phase: the proteins that will drive mitosis to completion are produced

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Mitosis Overview

  • Nuclear Division that occurs in four phases: Prophase, Metaphase, Anaphase, and Telophase (PMAT)

  • Spindle apparatus (fibers) moves toward chromosomes

    • Composed of two sets of microtubules

    • Extend from two poles of cell and overlap at the cell’s equator

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  • Chromosomes become visible as rodlike units, each consisting of two sister chromatids

  • Nuclear envelope begins to break down

  • Spindle apparatus move toward the poles

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  • Nuclear envelope fragments

  • Spindle apparatus attach to the centromere

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Metaphase (M&Ms)

  • Longest Stage of Mitosis

  • Nuclear membrane breaks up completely in the transition between pro- and metaphase

  • Chromosome aligns at the cell’s equator, halfway between the poles—also known as the metaphase plate

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  • Sister chromatids separate and move toward opposite poles

  • Spindle apparatus shorten and pull the chromosomes toward the poles

  • Once separated each chromatid is now an independent chromosomes

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  • Two daughter chromosomes of each original chromatid pair at opposite pair

  • Chromosome return to the threadlike form typical of chromosome

  • Each daughter cell has the same number of chromosomes as the parent cell

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  • Division of cytoplasm

  • Plants

    • Because of rigid cell wall, the cytoplasm of plant cells can not simply pinch off, the plant cell forms a cell plant to separate the two nucleus

    • Made from vesicles derived from the Golgi apparatus

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  • The flexible plasma membrane of animal cells can be squeezed in the middle to separate the two daughter cells

    • First sign of cleavage is the appearance of a cleavage furrow, a shallow groove in the cell surface near the old metaphase plate

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Mitosis is amazing!!!

  • Mitosis is accomplished with astonishing accuracy

  • There are times when mistakes happen (too many chromosomes or chromosomes deleted).

    • This is known as a mutation (genetic mistakes)

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Binary Fission

  • Prokaryotes cell division

  • 1- Bacterium have circular chromosomes replicate and move apart

  • 2- the point chromosome replication is known as origin of replication

  • 3- Each origin of replication will move opposite end of the cell

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  • 4- Cell elongates

  • 5- Cytoplasm begins to pinch in

  • 6- divides

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Cell Cycle Control

  • Cell cycle control system: a cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle

    • Checkpoint: in the cell cycle is a critical control point where stop and go-ahead signals can regulate the cycle

    • Animal cells generally have built in stop signals to halt the cell cycle

    • 3 major checkpoints: G1, G2, M phases

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Regulatory Proteins

  • 1- Kinases: drives the cell cycle

    • Present at constant concentration throughout the entire cell cycle throughout the entire cell cycle

  • 2- Cyclin: attaches to kinases

    • Cyclically fluctuating in the cell cycle

    • At checkpoint times is when you see the fluctuating

    • This helps the cell have the correct number of chromosomes

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Growth Factor

  • A protein released by certain cells that stimulates other cells to grow

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Density-dependent inhibition

  • Phenomenon in which crowded cells stop growing

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Loss of cells cycle in cancer cells

  • Cancer cells do not respond to the body’s control mechanisms

    • Transformation the process that converts a normal cell to a cancer cell

      • Immune system recognize a transformed cells and destroys it

      • However, if the cell evades destruction it may proliferate and form a tumor (a mass of abnormal cells within otherwise normal tissue)

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Two types of tumors

  • 1- Benign Tumor: abnormal cells remain at the original site

  • 2- Malignant tumor: becomes invasive enough to impair the functions of one or more functions (this is when a person have cancer)

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  • Spread of cancer cells to locations distant from their original site

    • This is usually done through the blood vessels and lymph vessels

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