Chapter 10: Cell Growth and Division

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Chapter 10Cell Growth and Division
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Cell Growth

• When an organism grows, the number of cells
  increase but the size of each cell remains small.

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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

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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

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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

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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

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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).

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• 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.

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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.

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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

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• 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

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• 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

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• 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
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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.

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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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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.

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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)

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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.

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• 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.

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Chapter 11-4 Meiosis
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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.

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• 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.

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haploid
haploid
diploid
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• 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.

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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.

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

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

Nucleus
centrioles
chromosomes (DNA)
Nucleus
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• 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.

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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.

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centrioles

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

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

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

centrioles
spindle
chromosome
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• 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
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Gamete formation

• In male animals, the haploid gametes are called
  sperm.
• In female animals, the haploid gametes are
  called eggs.

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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.

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Parts of a Chromosome
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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)

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• 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

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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.

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Centromere location
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Stem Cells
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What are stem cells?

• Stem cells are unspecialized cells that have the
  potential to differentiate into a wide variety of
  cell types.

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Stem Cell Guy

• http//learn.genetics.utah.edu/archive/stemcells/s
  cintro/

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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!

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Totipotent

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

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Adult Stem Cells

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

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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.

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Info on Stem Cells

• http//learn.genetics.utah.edu/archive/stemcells/s
  ctypes/