The Cell Cycle

1
Chapter 12

• The Cell Cycle

2
Cell Theory Principle

• Where a cell exists, there must have been a
  preexisting cell
• Omnis cellula e cellula
  (all cells come from cells) ,
  Rudolf Virchow

3
Necessary Characteristic of Life Cell
Reproduction

• unicellular organism
• reproduces entire organism
• multicellular
• growth
• embryonic development
• replacement of damaged or dead cells

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Binary FissionReproduction in Bacteria

• genome (hereditary endowment)
• single, circular dsDNA
• associated with proteins
• single chromosome
• replication averages minutes-3 hours

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Steps of Binary Fission

• 1. DNA replicates
• 2. cell increases in size
• increase cytosol
• 3. cell divides into two identical daughter cells

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Eukaryotes vs. Prokaryotes

• larger cell size
• greater quantity of DNA
• DNA associated with histones
• DNA divided into chromosomes

• smaller cell size
• lesser quantity of DNA
• DNA with some proteins
• one chromosome

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DNA Quantity in Eukaryotes

• Amount of DNA has no direct relationship to the
  complexity of that organism
• ex.
• Alligators have more DNA than humans
• frogs have more DNA than humans

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Chromosome Number in Eukaryotes

• Number of chromosomes has no direct relationship
  to complexity of that organism
• ex.
• Goldfish with 94 chromosomes, humans with 46

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DNA of Eukaryotes

• Chromosomes
• discrete entities
• condensed DNA protein
• state found when DNA division occurs

• Chromatin
• mass of DNA
• loose coils of DNA protein
• state found when DNA replication occurs

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Drawing of a Chromosome

• arms, short and long
• centromere DNA
• kinetochore protein,
  
  site where spindle
  fibers attach

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Eukaryotic Chromosome

• composition
• DNA 40
• protein 60
• length of an average human chromosome
• 5 cm

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Chromosome Appearance

• location of centromere varies
• size varies
• staining properties vary

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Karyotype

• particular array of chromosomes
• chromosomes of one cell are arranged according to
  size, number, and type
• information
• extra or missing DNA
• gender of individual

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Human Cells

• somatic cells body cells
• 46 chromosomes
• diploid (2n)
• gametes sex cells (sperm, ova)
• 23 chromosomes
• haploid number (1n or n)

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• homologous chromosomes
• pair of chromosomes
• one paternal, one maternal
• sister chromatids
• identical
• replicated forms of one chromosome
• held together by one centromere

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• autosomal chromosomes
• 22 pairs
• sex chromosomes
• 1 pair
• X X or XY

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Chromosomes

• Homologous (2) replicated (2)
• maternal, paternal sister
• chromatids

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Cell Cycle

• Interphase - nondividing phase
• G1 phase
• S
• G2 phase
• M (mitotic) phase - dividing phase
• mitosis
• cytokinesis

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Mitosis

• 2n (diploid)
• 2n
• (diploid)
• 2n (diploid)

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Interphase

• G1 phase (first growth phase)
• growth of cell, enough cytosol for 2
• S (synthesis)
• DNA replication, DNA in chromatin
• G2 phase (second growth phase)
• chromosome condensation
• microtubule synthesis
• replication of organelles

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M Phase(Mitotic phase)

• Mitosis (karyokinesis) - divide DNA
• prophase (prometaphase)
• metaphase
• anaphase
• telophase
• Cytokinesis - divide the cytoplasm

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Cell Cycle Duration

• varies from 1-24 hours
• ex. Human liver cell.22 hrs.
• Interphase G1 phase.9 hrs.
• S..10 hrs.
• G2 phase..2 hrs.
• M phase mitosis50 min.
• Cytokinesis.....10 min.

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Mitosis

• 2n (diploid)
• 2n
• (diploid)
• 2n (diploid)

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Microtubules polar (pos. and neg. ends)-

• - end
• at the centrosome
• nongrowing end

• end
• away from centrosome
• polymerization
• depolymerization

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Spindle Apparatusmade of microtubules

• away from
• centrosome
• pos
• neg centrosome end

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Cytokinesis

• Animal cell
• cleavage furrow
• microfilaments form contractile ring
• cell pinches in two

• Plant cell
• cell plate forms
• membrane-bound vesicles form plasma membrane
• cell wall material is deposited

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Controls of Cell Division

• Cells in tissue culture do not divide if
• essential nutrients are missing (growth
  factors)
• poisons that inhibit protein (microtubules)
  synthesis are present
• cells are crowded

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Controls of Cell Division, cont.

• they cannot progress beyond the restriction point
  in late G1
• insufficient concentration of MPF (maturation
  promoting factor, a complex of proteins)
• they have reached maximum division (20-50x for
  cells in culture)

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Cancer Cells

• express abnormal cell division
• density-dependent inhibition is absent
• divide excessively, immortal
• can invade other tissues (metastasis)
• genetically transformed
• can form malignant tumors
• can stop dividing at random points in the cycle

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Tumor

• mass of transformed cells
• benign tumor
• cells remain at original site
• lump can be completely removed
• malignant tumor
• invasive cells
• can impair functions of other organs

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Research

• Beginning to understand how a normal cell is
  transformed into a cancer cell
• Michael Bishop and Harold Varmus
• won Noble Prize
• demonstrated that genetic alterations can cause
  cancer

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Chapter 11

• The End