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Chapter 10: Cell Growth and Division

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Title: Chapter 10: Cell Growth and Division


1
Chapter 10Cell Growth and Division
2
Cell Growth
  • When an organism grows, the number of cells
    increase but the size of each cell remains small.

3
Limits to cell growth
  1. DNA overload The larger a cell becomes, the
    more demands the cell places on its DNA. a.    
    DNA stores the information that controls how a
    cell functions b.     When a cell is small, DNA
    can meet the cells needs c. When a cell is
    large, it still has only one copy of DNA so it
    is more difficult for the cell to perform its
    function

4
Limits to cell growth
  • 2. Exchanging materials In addition, large cells
    have more trouble moving substances across the
    cell membrane. a.     If a cell is too large,
    it is difficult to get enough oxygen and
    nutrients in and waste products out b. This is
    why cells do NOT grow much larger even if the
    organism does grow large

5
Division of the Cell
  1. Before a cell gets too large, it will divide to
    form two daughter cells
  2. Before a cell divides, it makes a copy of its DNA
    for each daughter cell

6
Chapter 10-2 Cell Division
  • Cell division in eukaryotes is more complex than
    in prokaryotes.
  • There are two stages of eukaryotic cell division
  • Mitosis Division of the cell nucleus
  • Cytokinesis Division of the cell cytoplasm
  • Unicellular organisms reproduce asexually by
    mitosis
  • a. The daughter cells are identical to the
    parents cells
  • 4. Mitosis is how a multicellular organism
    grows and develops

7
Chromosomes
  1. Chromosomes are made of condensed chromatin.
  2. Chromatin consists of DNA and the proteins it is
    wrapped around.
  3. The cells of every organism have a specific
    number of chromosomes (humans have 46
    chromosomes).

8
  • 3. Chromosomes are only visible during cell
    division, when they are condensed. The rest of
    the time the chromatin is spread throughout the
    nucleus.
  • Before cell division, each chromosome is
    replicated (meaning copied).a. When a chromosome
    is replicated, it consists of two identical
    sister chromatids.b. When a cell divides the
    chromatids separate, and one goes to each of the
    two new cells.
  • c. Sister chromatids are attached to
  • each other at the spot called the
  • centromere.

9
The Cell Cycle
  • When a cell is NOT dividing, it is said to be in
    interphase.
  • The series of events that a cell goes through as
    it grows and divides is called the cell cycle.

10
Events of the cell cycle
  • Interphase, when the cell is NOT dividing, has
    three phases G1, S, and G2.
  • 1.   G1 phase period of activity in which cells
    do most of their growing.
  • a.     Cells increase in size
  • b.     Cells synthesize (make) new proteins and
    organelles
  • 2.   S phase DNA (chromosomes) is replicated
  • 3. G2 organelles and molecules required for
    cell division are produced

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  • M phase is the phase of cell division. This
    includes
  • 1. Mitosis, the division of the cell nucleus,
    which is made up of four segments including
    prophase, metaphase, anaphase, and telophase.
  • 2. Cytokinesis, or the division of cytoplasm.

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Mitosis
  • There are four phases in mitosis
  • 1.     Prophase
  • a. Longest phase in mitosis (take 50- 60 of
    total time mitosis requires) b.    
    Chromosomes become visible because they are
    condensed

15
  • c.    Centrioles become visible on opposite
    sides of the nucleus
  • i. The centrioles help organize the spindle, a
    structure made of microtubules that helps
    separate the chromosomes
  • ii. Chromosomes attach to the spindle fibers
    near the centromere
  • iii.      Plant cells to not have centrioles
    but do have mitotic spindles
  • d.     Nucleolus disappears
  • e.    Nuclear envelope breaks down

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  • 2. Metaphase a.     Chromosomes line up in the
    center of the cell b. Microtubules connect to
    the centromeres

18
  • 3. Anaphase
  • a.     Centomeres split and the sister
    chromatids separateb.     The sister
    chromatids become individual chromosomes
  • c.      Chromosomes move and separate into
    two groups
  • near the spindle d. Anaphase ends when the
    chromosomes stop moving

19
  • 4. Telophase
  • a. Chromosomes change form being condensed to
    dispersed b. A nuclear envelope forms around
    each cluster of chromosomes c.   Spindle breaks
    apartd. Nucleolus is visible in each daughter
    nucleus

Telophase in the midbodies of two daughter cells
20
Cytokinesis
  • Mitosis occurs within the cytoplasm of one cell.
  • Cell division is complete when the cytoplasm
    divides.
  • In plants, a structure called the cell plate
    forms between the two daughter nuclei. The cell
    plate develops into a cell membrane and cell
    wall.

21
Cytokinesis
  • In animal cells, the cell membrane is drawn
    inward until the cytoplasm is pinched into two
    equal parts. Each part has a nucleus and
    cytoplasmic organelles.

The cleavage of daughter cells is almost
complete this is visualized by microtubule
staining
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Asexual Reproduction
  • Is one cell reproducing by itself
  • Two types
  • Binary Fission organism replicates its DNA and
    divides in half, producing two identical daughter
    cells
  • Example bacteria
  • Budding asexual process by which yeasts increase
    in number

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26
Chapter 10-3 Regulating the Cell Cycle
  • Different cell types divide at different rates.
  • Examples
  • Muscle cells and nerve cells do not divide once
    they have developed.
  • Skin cells and cells in the bone marrow that make
    blood cells divide rapidly.

27
Controls on cell division
  • Cell growth and cell division can be turned on
    and off.
  • When you are injured your cells divide rapidly to
    repair the injury. When the injury has healed,
    the cells stop dividing.
  • Cyclins regulate cell growth (add to notes)

28
Uncontrolled cell growth
  • When cells in your body CANNOT control cell
    growth and division, cancer may form.
  • 1. Cancer cells cannot respond to the signals
    that regulate the division of cells.
  • 2. When cancer cells have been dividing
    uncontrollably, tumors form. 3. Tumors can
    damage surrounding tissue. 4. Cells from tumors
    can break free and travel to other parts of the
    body, forming new tumors.

29
  • There are several reasons that cells may lose
    the ability to control growth.
  • Examples
  • 1. smoking
  • 2. radiation exposure
  • 3. viral infection
  • Scientists who study cancer are researching how
    cells divide.

30
Chapter 11-4 Meiosis
31
Chromosomes
  • You have 23 different pairs of chromosomes, for a
    total of 46 chromosomes.
  • One chromosome in each pair came from your mother
    and one from your father.

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  • Each chromosome in a pair is said to be
    homologous, meaning that the chromosome from the
    father has a corresponding chromosome from the
    mother.

34
  • Cells that contain both sets of homologous
    chromosomes are called diploid.
  • All of your cells except the sex cells (sperm and
    eggs also called gametes) are diploid. Gametes
    are haploid, meaning they contain only one copy
    of each chromosome.
  • When one sperm and one egg combine their DNA,
    there are two versions of each chromosome.

35
haploid
haploid
diploid
36
  • We use N to represent the haploid number of
    chromosomes and 2N to represent the diploid
    number of chromosomes.
  • 1. For humans, the haploid number is 23. We
    write this as N 23. The diploid number is
    46, which we write as 2N 46.
  • 2. In fruit flies, N 4 and 2N 8.

37
Meiosis
  • Meiosis is the process that divides one diploid
    (2N) cell to form four haploid (N) cells.
  • This process is a reductional division because
    the number of chromosomes per cell are cut in
    half.
  • Meiosis is how gametes are formed.

38
  • There are two divisions that occur in meiosis
    Meiosis I and Meiosis II.
  • 1. Before meiosis I begins, cells go through
    Interphase I.
  • 2. This involves DNA replication, forming a
    duplicate copy of each chromosome.
  • 3. Each chromosome is made of two sister
    chromatids.

centrioles
Nucleus with duplicated DNA that is not condensed.
cell
39
  • Meiosis I is similar to mitosis.
  • a.     Prophase I
  • i.      Centrioles are visible on opposite
    sides of the nucleus
  • ii.      Nucleolus disappears
  • iii.      Nuclear envelope breaks down

spindle
centrioles
DNA condensed as chromosomes
40
  • Iv iv. Homologous chromosomes pair
  • 1. When a pair of chromosomes aligns a tetrad
    is formed.
  • 2.      When chromosomes form a tetrad, they
    exchange portions of their chromatids in a
    process called crossing-over.
  • 3. Crossing-over produces new combinations of
    DNA.

tetrad
41
  • b.     Metaphase I
  • i.      Spindle fibers attach to the
    chromosomes at the centromere

spindle
centromere
centrioles
chromosomes (DNA)
42
  • c.     Anaphase I
  • i. Spindle fibers pull the homologous
    chromosomes toward opposite ends of the cell.
  • ii. Chromosomes move and separate into two
    groups near the spindle
  • iii. Anaphase ends when the chromosomes stop
    moving

spindle
chromosomes (DNA)
centrioles
43
  • d. Telophase I
  • i.      Nuclear membranes form around
    chromosomes
  • ii.      Daughter nuclei form
  • e. Cytokinesis
  • i. Cytoplasm divides

Nucleus
centrioles
chromosomes (DNA)
Nucleus
44
  • Meiosis I produces two haploid (N) daughter
    cells that have only one copy of each chromosome.
    (reductional division) Each chromosome is made
    of two sister chromatids.

45
Meiosis II
  • After Meiosis I, cells enter Meiosis II.
  • No DNA replication occurs between Meiosis I and
    Meiosis II.
  • Meiosis II separates the sister chromatids.

46
centrioles
  • a.     Prophase II
  • i. Centrioles are visible on opposite sides of
    the nucleus
  • ii. Nucleolus disappears
  • iii. Nuclear envelope breaks down

chromosome
47
  • b.     Metaphase II
  • i. Chromosomes align like they do in mitosis
  • ii. Chromosomes are attached to the spindle at
    the centromere.

centrioles
spindle
chromosome
48
  • Anaphase II
  • Sister chromatids separate and move towards
    opposite ends of the cell.

centrioles
spindle
chromosome
49
  • d.     Telophase II
  • i. Nuclear membranes form around chromosomes
  • ii. Daughter nuclei form
  • e.     Cytokinesis
  • i. Division of the cytoplasm
  • f.     Meiosis II produces four haploid (N)
    daughter cells

centrioles
nucleus
chromosome
50
Gamete formation
  • In male animals, the haploid gametes are called
    sperm.
  • In female animals, the haploid gametes are
    called eggs.

51
Comparing mitosis and meiosis
  • Mitosis produces two genetically identical
    diploid (2N) cells. Mitosis allows an organisms
    body to grow and to replace cells. In organisms
    that reproduce asexually, new organisms are
    produced by mitosis.
  • Meiosis produces four genetically different
    haploid (N) cells. Meiosis produces gametes for
    use in sexual reproduction.

52
Parts of a Chromosome
5
  1. Chromatid
  2. Centromere
  3. p (short) arm
  4. q (long) arm
  5. Telomeres (protects the end of the chromosome and
    keeps it from fusing with other chromosomes)

53
  • Telomere is a region of repetitive nucleotide
    sequences at each end of a chromosome. Protects
    the end of the chromosome from deterioration or
    from fusion with neighboring chromosomes. The
    ends of the chromosome
  • Centromere The primary constriction of the
    chromosome. The centromere also divides the
    chromosome into a short arm (p) and a long arm
    (q). All chromosomes have a short arm and a long
    arm
  • Chromatid A single molecule of DNA

54
Homologous Chromosomes
  • Homologous chromosomes (also called homologs or
    homologues) are chromosome pairs of approximately
    the same length, centromere position, and
    staining pattern, with genes for the same
    characteristics at corresponding loci (space or
    place). One homologous chromosome is inherited
    from the organism's mother the other from the
    organism's father. They are usually not
    identical, but carry the same type of information.

55
Centromere location
56
Stem Cells
57
What are stem cells?
  • Stem cells are unspecialized cells that have the
    potential to differentiate into a wide variety of
    cell types.

58
Stem Cell Guy
  • http//learn.genetics.utah.edu/archive/stemcells/s
    cintro/

59
Embryonic Stem Cells
  • Embryonic stem cells have potential to
    differentiate into any type of cell.
  • This occurs at fertilization and it has not
    developed features characteristic of the human
    body.
  • They must be harvested from developing embryos
    very early!

60
Totipotent
  • Totipotency is the ability of a single cell to
    divide and produce all the differentiated cells
    in an organism, including extraembryonic tissues

61
Adult Stem Cells
  • Stem cells present in already developed human
    tissues.
  • These stem cells can only differentiate into a
    limited range of cell types.

62
Multipotent
  • Multipotent  have the potential to give rise to
    cells from multiple, but a limited number of
    lineages.
  • a blood stem cell that can develop into several
    types of blood cells, but cannot develop
    into brain or other types of cells.

63
Info on Stem Cells
  • http//learn.genetics.utah.edu/archive/stemcells/s
    ctypes/
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