Cell Structure and Function

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Cell Structure and Function
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The Cell Theory

• All living things are made of one or more cells
• All cells come from pre-existing cells
• Cells are the basic unit for structure and
  function of all organisms

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Cell structure

• All cells are surrounded by a plasma (cell)
  membrane
• Cells contain organelles - small structures
  inside cells that perform various jobs
• All cells can be divided into two main categories

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Prokaryotic vs. Eukaryotic Cells

• Prokaryotic
• no nucleus
• Very small (1-10 um)
• Have very few organelles

• Eukaryotic
• have a nucleus
• Larger 10-100um (some larger)
• Have many organelles

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Eukaryotic Cells

• Plant and animal cells are eukaryotic as well
  fungi and protists (amoeba, paramecium, etc)
• Plant and animal cells have important differences
  (see diagrams)

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Eukaryotic Cellular Organization

• Single celled organisms (unicellular)
• Multiple celled organisms (multicellular)
• - in multicellular organisms, cells
• become specialized (do a particular
• job)

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Plasma (cell) membrane

• Consists of a double layer of lipids
• The outside and inside of the membrane is
  hydrophilic (water-loving)
• The interior of the membrane is hydrophobic
  (water-fearing)
• Substances must cross the membrane to enter and
  exit the cell

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Types of Membrane Transport

• Passive Transport (requires NO energy)
• Moves substances from a high to a low
  concentration
• Diffusion osmosis, facilitated diffusion
• Active Transport (requires energy)
• Substances move from a low to a high
  concentration
• Endocytosis exocytosis

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Concentration gradient

• Passive transport moves substances WITH (or DOWN)
  their concentration gradient
• Active Transport moves substances AGAINST their
  concentration gradients

PASSIVE TRANSPORT
HIGH LOW
ACTIVE TRANSPORT
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Diffusion

• Movement of a substance from a high concentration
  to a low concentration

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Osmosis

• Movement of water from a high water concentration
  to a low water concentration

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Osmosis in Different Cellular Environments

• Hypotonic - solution with a lower solute
  concentration than the cytoplasm of the cell
• Hypertonic - solution with a higher solute
  concentration than the cytoplasm of the cell
• Isotonic - has same solute concentration as the
  cytoplasm of the cell

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• Turgor pressure - pressure (from water) pushing
  against the cell wall of a plant (makes plant
  cells firm)
• Plasmolysis - shrinking of the cytoplasm of a
  cell caused by the loss of water (causes plants
  to wilt)

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Facilitated Diffusion

• Diffusion using membrane protein channels
• Some substance must use protein channels since
  they cannot pass through the lipid layer of the
  membrane

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Active Transport

• Requires the input of energy to move a substance
  against its concentration gradient (low to high)
• Energy is used in the form of ATP (energy
  molecule produced in mitochondria)

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Types of Active Transport Endocytosis,
Exocytosis and Ion Pumps

• Endocytosis - cell takes in substances too large
  to pass through the membrane
• Exocytosis - cell gets rid of large substances
• Ion pumps - pump ions against their concentration
  gradient

See endocytosis and exocytosis in action