Cell Reproduction

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Cell Reproduction

• 8.1 Chromosomes
• 8.2 Cell Division
• 8.3 - Meiosis

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What factors limit cell size?

• Diffusion
• DNA Content
• Surface area-to-volume ratio

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DIFFUSION

• Certain materials needed for the survival of the
  cell can only enter through diffusion.
• Ex. waste, carbon dioxide, oxygen
• Diffusion is only efficient over a short
  distance.
• A 20 cm cell would have to wait several months to
  receive the above listed molecules

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DNA CONTENT

• Most cells have only 1 nucleus
• The DNA in the nucleus makes RNA and releases it
  to the cytoplasm where it directs the production
  of enzymes
• Lack of enzymes Lack of cellular metabolism
• Some large cells have compensated by having
  multiple nuclei.

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Surface area-to-volume ratio

• If you double the size of a cell
• -It has 8x as much volume
• -Gives rise to 8x as much waste and need for
  nutrients
• -It becomes impossible for diffusion to keep up
  with the cellular demands

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Chromosomes

• Rod-shaped structures made of DNA and protein
• Coiled chromatin chromosomes
• Histones proteins that help maintain the shape
  of the chromosome

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Types of Chromosomes

• Sex Chromosomes
• X or Y chromosomes
• Determine sex of individual
• Autosomes
• Non-sex chromosomes
• Determine all other characteristics or traits
• Ex. Hair color, eye color, hemophilia

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Chromosome Number

• Diploid
• Having 2 sets of chromosomes (2n)
• Creates genetic diversity
• Hapliod
• Contain one set of chromosomes (n)
• Sex cells

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Two major stages of the cell cycle

• Interphase the growth period of time where cell
  activities are carried out
• -most of the cells life
• Mitosis process of nuclear division, followed
  by the division of the cytoplasm

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INTERPHASE

• What is going on during this time?
• G1 Phase
• Metabolism making ATP
• Cell growth, maintenance, repair
• S Phase
• Chromosomes are replicated (ready for mitosis)
• Make new proteins
• Synthesizing new organelles
• Conducting photosynthesis (autotrophs)
• Storing excess glucose (starch, glycogen)
• G2 Phase
• Final preparation before cell division (mitosis)

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Stages of Mitosis

• Prophase
• Metaphase
• Anaphase
• Telophase

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PROPHASE

• First stage of mitosis
• Longest phase of mitosis
• Chromatin the nucleus becomes visible chromosomes
• Nucleus disappears
• The chromatin, which was copied during interphase
  forms 2 complete sets of chromosomes called
  sister chromatids
• Spindle fibers form between pairs of centrioles

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METAPHASE

• Second stage of mitosis
• Chromosomes move to the equator of the cell
• Spindle fibers attach to each chromatid by its
  centromere

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ANAPHASE

• Third stage of mitosis
• Chromosomes separate at the centromere
• Each sister chromatid begins to move to opposite
  ends of the cell

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TELOPHASE

• Fourth stage of mitosis
• Two daughter cells are formed
• Each new cell has a complete set of chromosomes
• The cytoplasm then divides (cytokinesis)
• Nucleus reappears
• Chromosomes uncoil to form chromatin
• Interphase begins

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Control of the Cell Cycle

• Cellular enzymes and genes play a key role in
  checking and balancing cell division
• Tells cells when to divide/stop
• Proto-oncogene regulates cell growth, division
  and the ability for cells to adhere to one
  another
• Mutation of the proto-oncogene causes an
  oncogene
• ONCOGENE UNCONTROLLED CELL DIVISION

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Control of the Cell Cycle (2)

• Contact inhibition cell to cell communication
  between neighboring cellsstops the cellular
  division
• Eliminates an over-production of certain types of
  cells within the body.

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CANCER a loss of control

• Cancer an uncontrolled dividing of cells
• Caused by a change in one or more of the genes
  synthesizing enzymes to control the cell cycle
  (genetic factor)
• The cancer genes are often expressed when
  environmental conditions change (environmental
  factor)

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How can cells regain control

• Some genes act as brakes to suppress cancer
  expression
• Tumor-suppressor genes code for proteins that
  prevent cell division from occurring too often
• To get cancer, these tumor suppressor genes (all
  3 of them) must be damaged

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Carcinogen

• Any substance that can induce or promote cancer
• Most carcinogens are mutagens
• Cause mutation within the cell
• Known carcinogens include
• Chemicals in tobacco smoke
• Radiation
• UV light
• Certain viruses

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MEIOSIS
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INTERPHASE
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INTERPHASE MAIN EVENTS

• Chromatin replicates
• Just like in mitosis
• Forms 2 identical chromatids
• Centriole pairs replicate (animal cells only)

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PROPHASE I
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PROPHASE I MAIN EVENTS

• Chromatin condenses into chromosomes
• Tetrad forms by synapsis
• Crossing over occurs between homologous
  chromosomes
• Centriole pairs move apart
• Nuclear envelope and nucleoli disappear

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METAPHASE I
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METAPHASE I MAIN EVENTS

• Tetrads align along the metaphase plate
• Centromeres of homologous chromosomes point
  toward opposite poles
• Attach to spindle fibers

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ANAPHASE I
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ANAPHASE I MAIN EVENTS

• Homologous chromosomes separate
• Sister chromatids move as a unit
• remain attached at the centromere

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TELOPHASE I AND CYTOKINESIS
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TELOPHASE I MAIN EVENTS

• Chromosomes reach poles
• Still as sister chromatids
• Cytokinesis occurs simultaneously
• Interkinesis
• No DNA replication before meiosis II

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MEIOSIS II MAIN EVENTS

• Very similar to mitosis
• PII spindles form
• MII chromosomes align
• AII centromeres split
• TII nuclei reform
• Cytokinesis 4 haploid cells

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PROPHASE II
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METAPHASE II
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ANAPHASE II
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TELOPHASE II AND CYTOKINESIS
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KEY DIFFERENCES BETWEEN MEIOSIS AND MITOSIS

• Meiosis is reduction division
• 2n to n
• Meiosis creates genetic variation
• Meiosis is 2 successive nuclear divisions
• Meiosis I separates pairs of chromosomes
  centromeres do not divide

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GAMETE PRODUCTION THROUGH MIEOSIS

• Spermatogenesis
• Creates 4 sperm cells
• Oogenesis
• Creates 1 ootid (egg cell)
• 3 polar bodies (nonfunctional)

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ASEXUAL REPRODUCTION

• Production of offspring from one parent without
  the union of gametes
• Occurs only by mitosis

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SEXUAL REPRODUCTION

• Production of offspring through meiosis and the
  union of gametes
• Offspring genetically different due to genetic
  recombination
• Parts of chromatids can be exchanged (crossing
  over)
• Homologous pairs separate