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Cell Reproduction

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Title: Cell Reproduction


1
Cell Reproduction
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Reproduction of Prokaryotes
  • Prokaryotes reproduce through a process called
    binary fission
  • The single, circular chromosome (which is
    attached to the plasma membrane) replicates
  • The cell grows elongates, separating the two
    chromosomes
  • The plasma membrane and cell wall pinch inward,
    eventually forming two daughter cells

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Eukaryotic Chromosomes and Cell Division
  • Almost all of a eukaryotic cells genes are found
    in the cells nucleus, and are grouped into
    multiple chromosomes
  • Chromosomes are only visible when a cell is in
    the process of dividing
  • The rest of the time, the DNA protein threads
    exist as a diffuse mass called chromatin

5
  • Before dividing, the eukaryotic cell replicates
    its chromosomes
  • The two copies of the chromosome are called
    chromatids, and they are connected to each other
    at a region called the centromere
  • The pair of chromatids is still only one
    chromosome, and the chromatids are not considered
    chromosomes until they separate from one another

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The Eukaryotic Cell Cycle
  • A eukaryotic cell spends most of its time in
    interphase, the period of time between cell
    divisions
  • During interphase, metabolic activity is high
    the cell grows, produces cell parts, and in the
    middle of interphase the cells chromosomes
    duplicate
  • Interphase accounts for 90 of the total time
    required for the cell cycle

8
Interphase
  • Interphase may be divided into three subphases
  • The first subphase is called G1 (the G is for
    gap) the cell is producing proteins and
    organelles
  • The second subphase is the S phase, which is when
    DNA synthesis occurs
  • The third subphase is called G2, which is a time
    of metabolic activity proteins needed for cell
    division are produced

9
Mitotic Phase (M Phase)
  • Consists of two processes mitosis and
    cytokinesis
  • During mitosis, the chromosomes divide and are
    distributed into two daughter nuclei
  • During cytokinesis, the cytoplasm is divided into
    two
  • These two processes result in the production of
    two genetically identical daughter cells

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Phases of Mitosis - Prophase
  • Chromatin fibers condense
  • Nucleoli disappear
  • Each chromosome has two chromatids joined at the
    centromere
  • The spindle begins to form microtubules grow out
    of the centrosomes, which contain centrioles
  • The nuclear envelope fragments

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  • Microtubules grow until they can reach the
    chromosomes
  • Each chromatid has a special region at the
    centromere, called the kinetichore, where the
    spindle will attach
  • Spindles that dont attach to kinetichores extend
    toward the opposite side of the cell
  • The chromosomes begin moving toward the center of
    the cell

13
Phases of Mitosis - Metaphase
  • The spindle is fully formed
  • All of the centromeres of the chromosomes are
    lined up at the metaphase plate (the middle of
    the cell)
  • The kinetichores of the chromatids face opposite
    sides of the cell

14
Phases of Mitosis - Anaphase
  • The centromeres of the chromosome come apart and
    the sister chromatids separate (they are now
    considered daughter chromosomes)
  • Motor proteins on the kinetichores walk the
    chromosomes toward opposite sides of the cell
  • Kinetichore microtubules shorten and
    non-kinetichore microtubules lengthen (the cell
    elongates)

15
Phases of Mitosis - Telophase
  • Basically the reverse of prophase
  • Cell elongation that began in anaphase continues
  • Daughter nuclei appear-nuclear envelope appears
  • Chromatin fibers uncoil
  • Nucleoli reappear
  • Spindle disappears

16
Cytokinesis
  • Occurs along with telophase
  • In animal cells, cytokinesis involves a cleavage
    furrow, which pinches the cell in two
  • In plants, cytokinesis involves a cell plate,
    which grows outward and accumulates cell wall
    material

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The Cell Cycle Cancer
  • Cancer is a disease of the cell cycle
  • Systems that control the cell cycle do not work
    in cancer cells
  • As a result, cancer cells divide excessively and
    can invade other body tissues
  • The excessive growth can result in an abnormal
    mass called a tumor

26
Tumors
  • Benign tumor-abnormal mass of normal cells can
    cause problems if they grow in an organ remain
    in their original site can usually be completely
    removed by surgery
  • Malignant tumor-cancerous capable of spreading
    to other body areas displaces normal tissue can
    form new tumors by breaking apart and spreading
    through the circulatory system (called metastasis)

27
Types of Cancers
  • Carcinomas-originate in the external or internal
    coverings of the body (skin)
  • Sarcomas-originate in tissues that support the
    body (bone and muscle)
  • Leukemias and Lymphomas-cancers of blood forming
    tissues (bone marrow, spleen, and lymph nodes)

28
Treatments for Cancer
  • Radiation- parts of the body with cancerous
    tumors are exposed to high energy radiation,
    which disrupts cell division (damage to ovaries
    or testes may cause sterility)
  • Chemotherapy-administration of drugs that disrupt
    cell division some interfere with the formation
    or functioning of the spindle

29
Meiosis
  • Essential for the formation of gametes (ova and
    sperm) that will be used for sexual reproduction
  • Occurs in two consecutive cell divisions
  • Reduces the chromosome number by ½ (for humans,
    this means creating gametes that have 23
    chromosomes)

30
Human Chromosomes
  • Occur in pairs (there are 23 pairs) in somatic
    cells (typical body cells) these are called
    diploid cells (di2)
  • Occur unpaired (a single set of 23) in the
    gametes these are called haploid cells
  • The paired chromosomes in somatic cells are
    called homologous chromosomes, because they have
    genes for the same traits

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Human Chromosomes
  • 22 of the chromosome pairs are called autosomes
  • The 23rd pair consists of the sex chromosomes
  • Human females have a pair of sex chromosomes
    called X chromosomes (XX)
  • Human males have one X chromosome and one Y
    chromosome (XY)

33
Inheritance of Human Chromosomes
  • One chromosome from each pair is inherited from
    our mothers, and the other chromosome in the pair
    is inherited from our fathers
  • At the time of fertilization, the two haploid
    gametes (sperm and ovum) unite to form a diploid
    cell called the zygote
  • Fertilization results in the formation of a
    diploid cell, thus restoring the normal diploid
    number of human chromosomes

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Meiosis Produces Gametes
  • Meiosis occurs in the reproductive organs
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