Cell Growth and Division

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Cell Growth and Division
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Why do cells divide?

• DNA Overload
• Not enough information for a big cell
• Exchanging Materials
• Must be able to obtain nutrients and eliminate
  wastes easily
• Ratio of Surface Area to Volume
• Volume increases faster than the surface area

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Surface Area vs. Volume
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Chromosomes

• DNA and proteins
• Each chromosome consists of two identical sister
  chromatids
• Centromeres area where the chromatids are
  attached

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The Cell Cycle

• Series of events that cells go through as they
  grow and divide
• 4 phases
• M phase (mitosis and cytokinesis) the division
  of the nucleus and the cell
• G1 phase (the first gap) cells increase in
  size and synthesize new proteins and organelles
• S phase (synthesis of DNA) the chromosomes are
  replicated
• G2 phase (the second gap) many of the
  organelles and molecules needed for mitosis are
  produced

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The Cell Cycle
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The Cell Cycle

• Interphase G1 S G2
• M phase
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis

Mitosis
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Interphase

• Cell spends most of its time in interphase
• Cell grows
• Carrying out basic cell functions
• Making organelles
• Copying chromosomes

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Prophase

• Nucleoli disappear
• Chromatin condenses (becomes shorter thicker)
• Chromosomes become visible
• Centrioles separate move to opposite poles
• Spindle fibers form between the centrioles
• Nuclear membrane disappears

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Metaphase

• Chromosomes attach to the spindle fibers at the
  centromere
• Chromosomes align at the equator

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Anaphase

• Centromeres split apart
• Chromatids separate move apart
• Sister chromatids are pulled to opposite poles

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Telophase

• Cell membrane pinches together at the equator
• Nucleoli reappear
• Nuclear membrane encloses each set of chromosomes
• Chromosomes loosen up

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Cytokinesis

• Division of the cytoplasm
• Begins during telophase
• Cell membrane continues pinching until it
  separates forming 2 daughter cells
• Plant cells have a cell plate that forms

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Videos
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Life Spans of Human Cells
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Controls on Cell Division

• Cell-to-cell contact when cells come in contact
  with other cells, they stop dividing

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Cell Cycle Regulators

• Cyclin a protein which regulates the cell cycle
• Cyclins bind to enzymes called cyclin-dependent
  kinases
• Different cyclin/CDK combinations control
  different activities throughout the cycle
• Quality control checkpoints occur throughout the
  cycle
• If something goes wrong the cycle stops

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Cell Cycle Regulation
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Cell Cycle Regulators

• Internal regulators proteins that respond to
  events inside the cell
• Part of the checkpoint process
• External regulators proteins that respond to
  events outside the cell (e.g. growth factors)
• Direct cells to speed up or slow down the cell
  cycle

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Uncontrolled Cell Growth

• Cancer uncontrolled cell growth
• Cells no longer respond to the control mechanisms
• Occurs due to mutations in the DNA
• Cancer cells crowd out normal cells, resulting in
  loss of tissue function
• Tumor cluster of cancer cells
• Carcinogens cancer causing substances

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Cancer
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Apoptosis

• Programmed cell death
• Occurs when
• Webbing between human fingers and toes disappears
  before birth
• Leaves fall from trees
• Also occurs in cells with DNA damage to prevent
  cancerous growths

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Stem Cells

• Unspecialized cells that can become specialized
  under certain conditions
• Embryonic stem cells unspecialized cells from
  an embryo
• Can develop into a wide variety of specialized
  cells
• Adult stem cells found in certain types of
  tissues
• Might be able to develop into different types of
  cells