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Chapter 9 Cell Division-Proliferation and Reproduction

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Title: Chapter 9 Cell Division-Proliferation and Reproduction


1
Chapter 9Cell Division-Proliferation and
Reproduction
2
Cell Division
3
Cell Division
  • Cell Division is where one cell becomes two
    cells.
  • Asexual Reproduction is where one parent cell
    divides into two identical cells.
  • Sexual Reproduction is where genetic information
    from two parent cells to create a unique
    individual cell.
  • Three Types of Cell Division
  • Binary Fission
  • Asexual Reproduction
  • Mitosis
  • Asexual Reproduction
  • Meiosis
  • Sexual Reproduction

4
Binary Fission
  • Binary Fission is form of asexual reproduction
    and cell division used by all prokaryotic and
    some eukaryotic organisms.
  • 1. The parent cell DNA duplicates, and the cell
    elongates
  • 2. Cell wall and plasma membrane begin to divide
  • 3. Cross-wall forms completely around divided DNA
  • 4. Cells separate, there are now two daughter
    cells that are identical

5
Binary Fission
6
Human Genome
  • Humans have 23 pairs of chromosomes. This makes
    a total of 46 chromosomes.
  • A karotype is a description of the number, size,
    and shape of chromosomes.

7
Somatic and Sex Cells
  • In humans, somatic (body) cells have two sets of
    chromosomes, a total of 46.
  • These cells are called diploid or 2N.
  • In humans, gametes (sperm or eggs) have one set
    of chromosomes, a total of 23. These are also
    known as sex or germ cells.
  • Gametes have exactly one copy of each chromosome.
  • These are known as haploid or N.

8
Chromosomes
  • What is a chromosome?
  • A chromosome is double-stranded DNA molecules
    coiled into a short, compact unit containing
    genetic material.
  • Chromatin is DNA wrapped around histone proteins.
    This is to keep them from getting tangled.

9
Chromosomes
  • Uncoiled, each of your chromosomes is about two
    inches long.
  • So, imagine all 46 of your chromosomes into a
    cells nucleus that is 5 microns in diameter.
  • This is the equivalent of fitting 46 strings,
    each the length of a football field into a
    baseball.

10
Chromsomes
  • A chromatid is one of two parallel parts of a
    chromosome.
  • Sister chromadtids are identical copies of a
    chromosome, attached by a centromere.

11
Cell Cycle
  • The cell cycle consists of all of the stages of
    growth and division for eukaryotic cells.
  • It is divided into Interphase and Mitosis.

12
Interphase
  • Interphase is where cells will continue in normal
    metabolic activities and begins to prepare for
    cell division. Interphase is the longest stage of
    the cell cycle.
  • G1 Stage
  • S Stage (Synthesis)
  • G2 Stage

13
G1 Stage
  • In the G1 stage of interphase, the cell will
    gather nutrients and other resources from its
    environment.
  • G1 is the first growth phase during the cells
    primary growth phase
  • If a cell will remain in the G1 phase for an
    extended period of time, it may be also called
    the G0 stage. This is because it is not moving
    forward in the cell cycle.

14
S G2 Stage
  • In the S Stage of Interphase, DNA replication
    occurs in the cell.
  • This leaves a cell with two identical copies of
    DNA for later on in the cell cycle.
  • The final part of interphase is the G2 Stage.
  • Final preparations are made before going into
    mitosis.
  • This includes making the proteins used for
    moving the chromosomes.

15
Mitosis
  • After interphase, mitosis is the process of the
    cell cycle where one parent cell will divide into
    two daughter cells. During mitosis, all cellular
    activity ceases.
  • Mitosis is divided into four parts.
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
  • Cytokinesis (division of
  • cytoplasm) typically follows
  • telophase.

16
Prophase
  • The first stage of mitosis is prophase. There
    are three important parts of prophase.
  • Chromosomes condense
  • Spindle and spindle fibers form
  • Nuclear membrane disassembles.

17
Prophase
  • In early prophase, two sets of microtubules,
    known as centrioles, begin to separate and move
    to opposite poles of the cell.
  • Attached to the centrioles, spindle fibers will
    help move the chromosomes later in mitosis.

18
Prophase
  • In later prophase, chromosomes begin to appear as
    2 chromatids connected at the centromere.
  • The nucleolus and nuclear membrane have
    disintegrated.
  • The spindle fibers have moved farther apart.
  • Chromosomes attach to the spindle fibers.

19
Metaphase
  • Metaphase, the second stage of mitosis, is where
    chromosomes align at the equatorial plane of the
    cell.
  • At the end of metaphase, the centromere holding
    the sister chromatids together divides.
  • Each chromatid is now known as a daughter
    chromatid.

20
Anaphase
  • Anaphase, the third stage of mitosis, the sister
    chromatids move toward opposite ends of the cell.
  • The kineochore is a
  • protein attached to
  • each chromatid at the
  • centromere.

21
Telophase
  • In telophase, the cell finishes mitosis
  • Spindle fibers disassembles.
  • Nuclear membrane re-forms
  • Chromosomes uncoil
  • Nucleolus reforms

22
Cytokinesis
  • At the end of telophase, cytoskinesis occurs.
    Cytokinesis is when the cytoplasm separate to
    form two separate cells.
  • For cytokinesis in animal cells, a cleavage
    furrow is formed. A cleavage furrow is an
    indention of the plasma membrane that pinches to
    the center of the cell. This splits the cell in
    two.

23
Cytokinesis
  • Yet, in plant cells, cytoplasm division occurs
    with a cell plate. The cell plate begins to form
    at the center of the cell and grows outward to
    the cell membrane.
  • After cytokinesis,
  • you have two
  • daughter cells. Two
  • exact copies.

24
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25
Controlling Mitosis
  • During cell division, there are checkpoints which
    use proteins to evaluate the health of a cell.
  • Proto-oncogenes will code for proteins that
    provide signals to the cell that will encourage
    cell division.
  • Tumor-supressor genes will code for proteins to
    signal stopping cell division

26
p53 Protein
  • The p53 gene will code for the p53 protein, which
    is a type of tumor-supressor gene.
  • If it detects damaged DNA at the end of the G1
    phase, it will send out enzymes to fix the
    problem.
  • If the cell is deemed healthy afterwards, it is
    able to undergo cell division.

27
p53 Protein
  • Yet, if the damage is too far beyond repair, the
    p53 protein will cause the cell to digest itself
    from the inside out, known as apoptosis.
  • The other healthy cells will undergo cell
    division to replace the lost cell.

28
p53 Protein
  • What is the p53 gene is mutated?
  • It would code for a p53 protein that might not
    be able to monitor for damaged DNA.
  • Mutations to the p53 gene appear in 40 of all
    cancers.

29
Cancer
  • Cancer is a disease caused by the failure to
    control cell division.
  • Mutagens are agents that mutate or chemically
    damage, DNA.
  • Carcinogens are mutagens that cause cancer.
  • Tar in cigarette smoke is categorized as both a
    mutagen and a carcinogen.

30
Cancer
  • There are several agents that gave been
    associated with high risks of cancer
  • Radiation
  • X-Rays
  • UV-A from tanning lamps, UV-B
  • Chemicals
  • Arsenic
  • Benzene
  • Asbestos
  • Food containing nitrates
  • Some have a prediposition to cancer due to their
    genetic backgrounds. Mutated DNA may be passed
    from parent to offspring

31
Cancer
  • When uncontrollable mitotic division occurs, a
    group of cells form called a tumor.
  • Tumor is a mass of cells not normally found in a
    certain portion of the body.
  • Benign tumor is a cell mass that does not
    fragment and spread beyond its original area of
    growth.
  • Malignant tumors can spread through other parts
    of the body.
  • Cells of malignant tumors metastasize, or move
    from the original site and begin to grow new
    tumors in other regions of the body.

32
Terminology
  • Haploid is a cell with ONE set of chromsomes (N)
  • Diploid is a cell with TWO sets of chromosomes.
    (2N)
  • Ultimately, one set comes from the haploid cells
    provided by each parent (N N 2N)

33
Terminology
  • Homologous chromosomes have the same appearance
    and genes.
  • Diploid cells will have many sets of homologous
    chromosomes

34
Terminology
  • Non-homologous chromosomes have different genes
    on their DNA.

35
Terminology
  • During the preparations for meiosis, the genetic
    information in a cell will be copied into sister
    chromatids.
  • At this point, sister chromatids are identical.
  • The purple sister chromatids on the right are
    homologous chromosomes to the green sister
    chromatids on the left because
  • 1. Same Genes
  • 2. Similar Shapes
  • 3. The centromeres holding sister chromatids are
    in the same location along the chromosomes.

36
Sexual Reproduction
  • Meiosis transforms diploid cells (2N) into
    haploid daughter cells (N)
  • Meiosis occurs only in diploid cells, not in
    haploid cells.
  • Fertilization, the fusion of two haploid cells,
    causes the transition from haploid (N) to diploid
    (2N).
  • Haploid cells that fuse are called gametes
  • This first diploid cell is called a zygote.
  • Depending on the organism, mitosis (asexual
    reproduction) may occur in haploid cells only,
    diploid cells only, or in both haploid and
    diploid cells.

37
Alternation of Generations-Human
  • In humans, the only haploid stages are gametes.
  • In males, spermatozoa begins at puberty and
    continues daily until at least age 70.
  • In females, oogenesis begins as a fetus.
  • This egg completes meiosis after fertilization by
    a sperm.

38
Alternation of Generations-Plant
  • In flowering plants and conifers, the dominant
    phase of the life cycle is also diploid.
  • Haploid cells are produced in anthers and in
    ovaries.
  • These haploid cells undergo a few cycles of
    mitosis to produce multicellular haploid stages.
  • Fusion of sperm (N) with egg (N) produces a
    zygote (2N)

39
Meiosis
  • In meiosis, chromosome copy once, divide twice.
  • Like mitosis, meiosis is preceded by interphase.
  • This is followed by two rounds of separating
    chromosomes to end up with four haploid cells.

40
Meiosis
  • Meiosis
  • Meiosis I
  • Prophase I
  • Metaphase I
  • Anaphase I
  • Telophase I
  • Meiosis II
  • Prophase II
  • Metaphase II
  • Anaphase II
  • Telophase II

41
Interphase
  • During interphase, the chromosomes are copied and
    the copies (sister chromatids) remain attached at
    the centromere.
  • The machinery necessary to move chromosomes
    (centrioles, etc.) is copied too.

42
Meiosis I
  • Prophase 1 begins as the chromosomes condense for
    packing.
  • Spindle fibers begin to form.
  • Homologous chromosomes pair up, these are known
    as tetrads.
  • Homologous chromosomes typically exchange some
    sections of DNA in a process called crossing over

43
Meiosis I
  • In metaphase I, all the tetrads are lined up
    midway between the two poles.
  • Anaphase I begins when the homologous chromatids
    in the tetrads release each other.
  • Spindle fibers pulls the homologous chromatids to
    opposite poles of the cell.
  • The homologous chromosomes are separated from
    each other segregated.

44
Meiosis I
  • In telophase I, the chromosomes begin to uncoil,
    the new nuclei form, and the cytoplasm splits.
  • The end of meiosis I produces two daughter cells,
    each with only half the unique genetic
    information of the parent

45
Meiosis II
  • The second cycle of division in meiosis is just
    like mitosis, except the chromosomes are not
    copied during interphase.
  • Spindle fibers attach to the centromeres of
    sister chromatids during prophase II.

46
Meiosis II
  • By metaphase II, all the sister chromatids are
    lined up midway between the two poles.
  • Anaphase II begins when the centromeres holding
    the sister chromatids split and the sisters
    become daughters.

47
Meiosis II
  • In telophase II, the new nuclei begin to form,
    chromosomes unwind, and the cell begins to
    divide.
  • During spermatogenesis, cytokinesis is equal.
  • During oogenesis, cytokinesis is unequal.

48
Meiosis
  • Meiosis is the key to sexual reproduction, which
    generates populations of genetically diverse
    individuals.
  • Among these individuals will be those whose
    characteristics allow them to thrive in a
    changing environment.

49
Genetic Diversity Mutations
  • Five processes are responsible for producing
    offspring which differ genetically from their
    parents.
  • 1) Mutations from point mutations to chromosomal
    mutations
  • Cystic fibrosis is a common lethal genetic
    disorder in the U.S.
  • It is caused by a mutation to a gene which
    produces proteins that regulate mucus production.

50
Genetic Diversity Segregation
  • As a result of meiosis, each haploid cell will
    inherit only one of the two alleles present in
    one parent.
  • Because homologous chromosomes end up in
    different cells during Meiosis I, the two
    parental alleles are segregated (separated).
  • Gametes will
  • have either the
  • allele for type A
  • blood or type O
  • blood

51
Genetic Diversity Crossing Over
  • During prophase of Meiosis I, homologous
    chromosomes exchange sections of DNA - crossing
    over.
  • This moves some alleles from one homologous
    chromosome to another
  • This creates new combinations of alleles.
  • Without crossing over, the purple homologous
    chromosome has alleles for type O blood, attached
    earlobes, and normal hemoglobin.
  • After crossing over, one purple chromatid has
    alleles for type O blood, attached earlobes, and
    sickle-cell hemoglobin

52
Genetic Diversity Crossing Over
  • Without crossing over, meiosis produces two
    unique haploid cells.
  • After a single cross-over, there are now four
    unique haploid cells.

53
Genetic Diversity Crossing Over
  • Crossing over can happen at multiple places
    between homologous chromosomes during Prophase I.
  • This additional crossing over events creates more
    unique combinations of alleles.
  • During meiosis in humans, 2-3 crossing over
    events occur between each pair of homologous
    chromosomes.

54
Genetic Diversity Independent Assortment
  • We know that each haploid cell will end up with
    one of two homologous chromosomes from
    segregation.

55
Genetic Diversity Independent Assortment
  • But the arrangement of one pair of homologous
    chromosomes has no impact on the arrangement of
    non-homologous chromosomes are inherited
    independently
  • Occurs in Metaphase.
  • Independent Assortment

56
Genetic Diversity Independent Assortment
  • In general, the number of possible combination of
    non-homologous chromosomes due to independent
    assortment
  • 2N, where N of haploid chromosomes
  • If N 1, then there are 21 2 unique gametes.
  • If N 2, then there are 22 4 unique gametes.
  • If N 3, then there are 23 8 unique gametes.
  • What about humans?
  • If we add in mutations and crossing over, each
    gamete is truly unique.

57
Genetic Diversity Random Fertilization
  • During fertilization, one unique sperm combined
    with one unique egg to create a zygote, the
    initial diploid stage.
  • In humans, that means one of the 8.3 x 106 unique
    sperm will combine with one of the 8.3 x 106
    unique eggs.
  • Each zygote is the product of these unique
    combinations.
  • Leads to 70 trillion unique compositions of
    diploid cells.

58
Nondisjunction
  • In meiosis, the number of chromosomes in diploid
    cells is reduced to haploid. However, there are
    cases, where homologous chromosomes do not
    segregate properly.
  • Nondisjunction occurs when homologous chromosomes
    do not separate during cell division.

59
Nondisjunction
  • If one of these abnormal gametes unites with a
    normal gamete, the offspring will have an
    abnormal number of chromosomes.
  • In monosomy, a cell has just one pair of
    homologous chromosomes.
  • In trisomy, a chromosome is present in three
    copies.
  • Down syndrome is a result of trisomy-21.
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