CH' 11 The Continuity of Life: Cellular Reproduction

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CH. 11 The Continuity of Life Cellular
Reproduction
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11.1 What Is the Role of Cellular Reproduction in
the Lives of Individual Cells and Entire
Organisms?

• So what is the cell cycle?
• The sequence of activities that occurs from
  one cell division to the next
• During cell division, the dividing cell is called
  a parent cell while the offspring is called a
  daughter cell

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A Parents Responsibility

• A dividing cell has to provide several things for
  its offspring
• Genetic information (DNA)
• Other cellular components it needs (such as
  mitochondria, ribosomes, and ER)

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Single Parents Exist in Other Organisms Too

• In asexual reproduction, offspring are formed
  from a single parent rather than through the
  union of gametes (sperm egg)
• Examples

Yeast
Hydra
Paramecium
Neurons (a body cell)
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The Cell Cycle

• Cells are made in a continuous process and
  whether a cell is prokaryotic or eukaryotic,
  there are three common steps
• 1. Growth
• 2. DNA replication
• 3. Cell division

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The Cell Cycle
Growth
Replication
Division
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A. The Prokaryotic Cell Cycle Consists of
Growth and Binary Fission

• Binary fission is cell division in prokaryotic
  cells which means splitting in two
• The DNA in a prokaryotic cell is usually circular
  and before splitting in two, the DNA is
  replicated during the long growth phase

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Keeping It in the FamilyLegally

• Because DNA replication produces two identical
  DNA molecules that will be passed on, the
  daughter cells are genetically identical to each
  other and to the parent cell
• The exception An occasional mutation
• Think backseveral of your babies had genetic
  disorders caused by point mutations (CF, PKU,
  Tay-Sachs)

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B. The Eukaryotic Cell Cycle Consists of
Interphase and Cell Division

• Eukaryotic cell division is variable because
  cells like those found in bone marrow and skin
  divide frequently while nerve and muscle cells
  are usually amitotic meaning they usually
  dont divide after maturity (therefore they are
  not replaced if damaged or destroyed)

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Interphase

• I. During Interphase, the Eukaryotic Cell Grows
  in Size and Replicates its DNA
• What three things occur?
• 1) The cell acquires nutrients from its
  environment,
• 2) growth, and 3) duplication of chromosomes
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• One copy of each chromosome and usually half the
  cytoplasm is also parceled out at this time

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The Subphases of Interphase

• G1 (gap or growth phase)-when the cell acquires
  or synthesizes the material needed for cell
  division
• S phase-when DNA synthesis occurs if the proper
  size has been reached and if the necessary
  signals have been received
• G2-completion of growth until cell division
  occurs
• However, sometimes after G1, differentiation
  occurs and this is known as cell specialization

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(Mitosis)
(Differentiation)
(Interphase)
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Mitosis Meiosis

• II. There are Two Types of Cell Division in
  Eukaryotic Cells Mitotic Cell Division and
  Meiotic Cell Division
• Mitotic cell division consists of nuclear
  division (called mitosis) and cytoplasmic
  division (called cytokinesis)
• Cytokinesis -the process by which the cytoplasm
  of a parent cell is divided between the two
  daughter cells
• So what does mitotic cell division enable
  multicellular organisms to do?
• Grow, maintain tissues (replace cells), and
  repair (even regenerate)
• Cells are also able to divide before they get too
  big

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Cell Size

• Remember, a cell has a lot of organelles to
  perform specialized functions. In order for them
  to work together quickly and efficiently, they
  need to be able to transport things VERY QUICKLY
  (by diffusion) therefore they have to be VERY
  small

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Sexual Reproduction

• A prerequisite for sexual reproduction in all
  eukaryotic organisms is meiotic cell division
  that occurs only in the testes and ovaries in
  animals
• This process involves a specialized nuclear
  division called meiosis and two rounds of
  cytokinesis to produce four daughter cells that
  can become gametes
• These gametes are eggs or sperm that carry half
  of the genetic material of the parent

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11.2 How is DNA in Eukaryotic Cells Organized
into Chromosomes?

• A. The Eukaryotic Chromosome Consists of a
  Linear DNA Double Helix Bound to Proteins
• How does the term locus show the relationship
  between chromosomes and genes?
• A locus is the actual location or place of the
  gene on the chromosome

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Specialized Regions on a Chromosome

• In addition to genes, other specialized regions
  of a chromosome are two telomeres and one
  centromere

• Telomeres are repeating nucleotide sequences
  found at the ends of a chromosome that are
  essential for chromosome stability
• The centromere attaches the sister chromatids
  together
• When the two sister chromatids are attached,
  the shape looks like the letter X.

Sister chromatid
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Eukaryotic Chromosomes

• B. Eukaryotic Chromosomes Usually Occur in
  Homologous Pairs with Similar Genetic Information
• The view of an entire set of stained chromosomes
  is called a karyotype and it reveals that most
  nonreproductive cells contain pairs of
  chromosomes.

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Eukaryotic Chromosomes

• Chromosomes that contain the same genes are
  called homologous chromosomes.
• What are cells called if they have pairs of
  homologous chromosomes? Diploid
• In humans, there are 23 pairs of chromosomes or
  46 in all. Chromosomes 1 through 22 are called
  autosomes and the X and Y chromosomes are the sex
  chromosomes.

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Eukaryotic Chromosomes

• Most cells within our bodies are diploid, but
  gametes are haploid. This means that they only
  contain one of each type of chromosome.
• The fusion of 2 haploid cells produces a diploid
  cell
• If n represents the haploid number of
  chromosomes, what represents the diploid? 2n

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The Cell Cycle (in Eukaryotes)

• I- Interphase
• Peed- Prophase
• Madly- Metaphase
• At- Anaphase
• The- Telophase
• Crapper- Cytokinesis

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The Cell Cycle

• Cell division occurs in a series of stages, or
  phases.

1st Interphase - Chromosomes are copied -
Chromosomes are in the form of chromatin -
Longest and busiest phase of the cell cycle
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The Cell Cycle Mitosis

• 2nd Prophase
• - Mitosis begins
• - Chromatin condenses to
• form chromosomes
• - Centrioles (pole-like organelles) appear
• - Spindle fibers form between the poles

spindle fibers
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The Cell Cycle Mitosis

• 3rd Metaphase
• - Chromatids attach
• to the spindle fibers
• - The chromosomes line
• up in the middle of the cell

spindles
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The Cell Cycle Mitosis

• 4th Anaphase
• - Centromeres at the center of
• the chromosome split and
• sister chromatids are pulled
• apart to opposite ends of the cell.

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The Cell Cycle Mitosis

• 5th Telophase
• - Two new nuclei are
• formed and a double membrane
• begins to form around them
• - Chromosomes loosen up to
• become chromatin again
• - Mitosis ends

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The Cell Cycle

• 6th Cytokinesis
• - Cell membrane moves inward
• and the cytoplasm divides
• - Two daughter cells are created-
• each with its own nucleus
• (with identical chromosomes)

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Why Meiosis?

• Each type of organism has a specific number of
  chromosomes (humans have 46 chromosomes)
• Because a each parent passes along a chromosome,
  there has to be some way for offspring to have
  the same number of chromosomes as their parents
  and not double

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Why Meiosis?

• Gametes that are produced are sperm cells for
  males and egg cells for females
• Sexual reproduction when haploid egg and sperm
  cells join together to form a diploid zygote
• In humans, each sperm and egg cell has 23
  chromosomes (which is half of 46, the normal
  number of chromosomes) or Sperm (23) Egg (23)
  Zygote (46)

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Why Meiosis?

• For the most part, healthy human zygotes cannot
  have more than 46 chromosomes
• Once formed, zygotes undergo mitosis to grow and
  develop (asexual reproduction)

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Before Meiosis

• Homologous chromosomes are attached to each other
• Homologous chromosomes 2 of the same type of
  chromosome
• Chromosomes copy themselves so that they can be
  passed along to the daughter cells

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Before Meiosis

• Tetrad 2 homologous chromosomes attached
  together ( 4 sister chromatids)

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Genetic Variation

• Genetic variation rearrangement of alleles
  that can produce completely new combinations
  (essential for evolution to occur)

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Genetic Variation

• Crossing Over- When the homologous chromosomes
  pair so tightly that a piece of the chromatid
  breaks off. The piece changes place with a piece
  from the other homologous tetrad. This scrambles
  the traits around genetic variety.

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Genetic Variation

• Genetic Recombination the reassortment of
  chromosomes and genetic material, either by
  crossing over or independent assortment, which
  increases genetic variety

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Genetic Variation

• Both crossing over and independent assortment are
  completely RANDOMso this is why humans can
  sometimes look completely different from other
  family members

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Meiosis I2 new cells are formed

• Prophase I
• Tetrads condense (2 homologous chromosomes
  attached together)
• Crossing over occurs between chromosomes
• Nuclear membrane disappears
• Centrosomes move to opposite ends of cell to form
  spindle fibers
• Metaphase I
• Tetrads line up in the middle of the cell

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Meiosis I

• Anaphase I
• Tetrads split and each set of sister chromatids
  moves to opposite ends of the cell
• Telophase I
• Cytokinesis (division of the cytoplasm) results
  in 2 new cells, each with homologous chromosomes

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Meiosis II

• (4 new cells are formed) LIKE MITOSIS
• Prophase II
• Centrosomes on the chromosomes form spindle
  fibers in preparation to be pulled apart
• Metaphase II
• Chromosomes (sister chromatids) line up randomly
  in the middle

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Meiosis II

• Anaphase II
• Sister chromatids separate and move to opposite
  ends of the cell
• Telophase II/Cytokinesis
• New nuclei are formed and four daughter cells are
  produced, each containing ONE chromosome from
  each homologous pair

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Mistakes in Meiosis

• Nondisjunction when homologous chromosomes
  dont separate from each other during meiosis
• So homologous chromosomes move together into a
  new gamete giving that gamete too many
  chromosomes, while the other new gamete is
  missing the chromosome

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Mistakes in Meiosis

• Organisms with extra chromosomes can survive
• Organisms with too few chromosomes usually do not
  survive

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Mistakes in Meiosis

• Polyploidy when organisms have more than the
  normal number of chromosome sets
• instead of 46 chromosomes, they might have double
  or triple that number
• Can be lethal for animals but not plants (plants
  just usually get bigger)

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Conditions that Result from Extra Chromosomes
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Comparing Mitosis and Meiosis