Cell Cycle and Mitosis

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Cell Cycle and Mitosis
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Cell Division

• The process by which a cell divides into two new
  daughter cells.
• Daughter cells are the NEW cells ? the product of
  cell division.

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Cell Division

• Before cell division occurs, the cell replicates
  (copies) all of its DNA.
• This solves the problem of information overload
• Each cell gets one complete copy of genetic
  information

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Cell Division

• Cell division also solves the problem of
  increasing size by reducing cell volume.
• Cell division results in an increase in the ratio
  of surface area to volume.
• This allows for the efficient exchange of
  materials within a cell.

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Cell Division and Reproduction

• Asexual Reproduction the production of
  genetically identical offspring from a single
  parent.
• Sexual Reproduction fusion of two cells
• The offspring produced by sexual reproduction
  inherit some of their genetic information from
  each parent.

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Asexual Reproduction

• Occurs in many single-celled organisms.
• Ex, bacterium
• Cell division
• Also occurs in multi-cellular organisms
• Budding small bud growing off hydra plant will
  eventually break off and become a new plant

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Advantages of Asexual Reproduction

• Asexual reproduction is very fast.
• If conditions are right, quick reproduction can
  be a very good thing.
• If conditions remain the same, genetically
  identical offspring is a good thing too.

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Disadvantages of Asexual Reproduction

• A lack of genetic diversity is a disadvantage
  when conditions change in ways that do not fit
  the characteristics of an organism.

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Sexual Reproduction

• Many animals and plants reproduce sexually
• Many single-celled organisms also reproduce
  sexually
• Offspring are produced by the fusion of special
  reproductive cells formed by each of two parents.

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Advantages of Sexual Reproduction

• Provides genetic diversity
• In a changing environment, genetic diversity
  provides the right combination of characteristics
  needed to survive.

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Disadvantages of Sexual Reproduction

• Process of finding a mate and raising offspring
  requires time.

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Chromosomes and the Cell Cycle

• Chromosome
• Threadlike structure within the nucleus that
  contains genetic information
• Bundle of DNA
• Replicated at the beginning of the cell cycle
• Passed on from parent cell to daughter cell

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Prokaryotic Chromosomes

• Prokaryotes lack nuclei
• Most prokaryotes contain a single, circular DNA
  chromosome that contains all, or nearly all, of
  the cells genetic information.

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Eukaryotic Chromosomes

• Eukaryotic cells usually have more DNA than
  prokaryotes.
• Eukaryotes contain multiple chromosomes.
• Fruit flies have 8 chromosomes per cell.
• Humans have 46 chromosomes per cell.

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Eukaryotic Chromosomes

• Chromosomes make it possible to separate DNA
  precisely during cell division.
• Chromosomes form a close association with
  histones (type of protein).
• This complex of chromosomes and proteins is known
  as chromatin.

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Chromatin
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Cell Cycle

• During the cell cycle, a cell grows, prepares for
  division, and divides to form two daughter cells.

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Prokaryotic Cell Cycle

• The process of cell division in prokaryotes is a
  form of asexual reproduction.
• This process is known as binary fission.

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Eukaryote Cell Cycle

• Consists of 4 phases
• G1 phase
• S phase
• G2 phase
• M phase

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Interphase

• Period of cell cycle between cell divisions.
• Divided into 3 phases
• G1 phase
• S phase
• G2 phase

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G1 Phase

• Cells do most of their growing during G1 phase.
• Cells increase in size during this phase.
• Cells synthesize new proteins and organelles
  during this phase.

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S Phase

• S stands for synthesis (to make).
• During this phase, new DNA is synthesized (made)
  when the chromosomes are replicated (doubled).
• The cell at the end of this phase contains twice
  as much DNA as it did at the beginning.

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G2 Phase

• During this phase, many of the organelles and
  molecules required for cell division are
  produced.
• Chromatid one of two identical sister parts
  of a duplicated chromosome
• Centromere region of a chromosome where the two
  sister chromatids attach
• Centriole structure in an animal cell that
  helps to organize cell division

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M Phase

• Two new daughter cells are produced during this
  phase.
• M comes from the word mitosis.
• This phase has two stages
• Mitosis
• Cytokinesis
• In many cells, this process may overlap.

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Mitosis

• Consists of 4 stages
• Prophase
• Metaphase
• Anaphase
• Telophase

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Prophase

• During prophase, the genetic material inside the
  nucleus condenses and the duplicated chromosomes
  become visible.
• Outside the nucleus, a spindle starts to form.
• Cell starts to build spindles
• Spindles fanlike system of microtubules that
  will help to separate the duplicated chromosomes.
• Spindle fibers extend from tiny paired structures
  called centrioles

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Prophase and Centrioles

• Centrioles are only found in animal cells.
• During prophase centrioles start to move toward
  opposite ends (poles) of the cell.
• As prophase ends, the chromosomes coil more
  tightly, the nucleolus disappears, and the
  nuclear envelope breaks down.

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Prophase
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Metaphase

• During metaphase, the centromeres of the
  duplicated chromosomes line up across the center
  of the cell.
• Spindle fibers connect the centromere of each
  chromosome to the two poles of the spindle.

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Metaphase
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Anaphase

• During anaphase, the chromosomes separate and
  move along spindle fibers.
• Once anaphase begins, each sister chromatid is
  now considered an individual chromosome.
• Anaphase comes to an end when this movement stops
  and the chromosomes are completely separated into
  two groups.

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Anaphase
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Telophase

• During telophase, the chromosomes, which were
  distinct and condensed, begin to spread out in
  into a tangle of chromatin.
• A nuclear envelope reforms around each cluster of
  chromosomes.
• The spindle begins to break apart.
• A nucleolus becomes visible in each daughter
  nucleus.

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Telophase
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Cytokinesis

• Cytokinesis completes the process of cell
  division it splits one cell into two.
• This process is different in animal cells and in
  plant cells.

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Cytokinesis in animal cells

• The cell membrane is drawn inward until the
  cytoplasm is pinched into two nearly equal parts.

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Cytokinesis in plant cells

• The cell membrane is not flexible enough to pinch
  because of the rigid cell wall.
• A structure known as the cell plate forms halfway
  between the divided nuclei.
• The cell plate gradually develops into cell
  membranes that separate the two daughter cells.
• A cell wall then forms in between the two new
  membranes.

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Cytokinesis in plant cells