Summary: Cell Cycle And Mitosis

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• 1 Cell cycle and mitosis

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• A.Cell cycle

  a.G1, S, G­2, M

• a.Interphase – G1, S, G2

  i.Longest part of cycle
  ii.Cells not dividing spend time in G0 stage, fxn without preparation for division
  iii.Individual chromosomes not visible – less condensed form of chromatin so that DNA is available to RNA polymerase during transcription

• a.G1 stage: Presynthetic gap

  i.Cells create organelles for energy and protein production (ribosomes, mitochondria, ER)
  ii.Cells increase in size
  iii.Passage into S phase governed by restriction point – certain criteria must be met
  iv.Protein p53  responsible for DNA repair

• a.S phase: synthesis of DNA

  i.Cell replicates genetic material
  ii.After replication, each chromosome consists of identical chromatids bound together at  centromere

• a.G2 – postsynthetic gap 

  i.Quality control checkpoint

• a.M stage – Mitosis

  i.Mitosis and cytokinesis
  ii.Prophase, metaphase, anaphase, telophase
  iii.Occurs in somatic cells not involved in reproduction

• a.Prophase I

  i.Chromatin condenses, spindle apparatus forms, nuclear envelope disappers
  ii.Homologous chromosomes come together in synapsis, forming tetrads, held together by synpoptonemal complex
  iii.Chromatids break at chiasma and exchange pieces in crossing over btw homologous chromosomes, not sister chromosomes – genetic recombo
  1.à responsible for Mendels second law of independent assortment

• a.Metaphase I

  i.Tetrads align at equator

• a.Anaphase I

  i.Homologous pairs separate in disjunction  or segregation
  1.Accounts for Mendels first law of segregation
  a.Maternal and paternal chromosomes separate, and either can end up in either daughter cell

• a.Telophase I

  i.Nuclear membrane forms around each new nucleus
  ii.Haploid cells (n)
  iii.Interkenesis – short rest when chromosomes partially uncoil