CELL BOUNDARIES

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CELL BOUNDARIES

• The Cell Membrane and Transport Processes

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I. The Structure and Function of the Cell Membrane
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• Components of the cell membrane
• Phospholipid bilayer nonpolar fatty acid tails
  turn inside, polar phosphate heads turn outside
  forms a flexible structure as a boundary
• Proteins can be integral proteins or peripheral
  proteins. They can act as enzymes, receptors,
  transport and binding molecules
• Carbohydrates Identification tags outside of
  the cell membrane (glycolipids and glycoproteins)
• Cholesterol helps stabilizing the membrane by
  making it more solid animal cells

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The Function of the Cell Membrane

• Surrounds the cell.
• Regulate the transport of molecules in and out of
  the cell -- semipermeable
• Immune response
• Attaches the cells to other cells or surfaces.
• The model that describes cell membrane, the Fluid
  Mosaic Model
• http//www.youtube.com/watch?vGW0lqf4Fqpg
• http//www.youtube.com/watch?vQqsf_UJcfBc

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Selective Permeability

• Cell membranes control what goes in and out of
  the cell
• It allows some substances to cross more easily
  than others

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II. Passive Transport Processes

• Transport means the movement of molecules from
  one side of the cell membrane to the other
• Transport is influenced by
• The size of substances
• The polarity of substances
• The concentration of substances
• The permeability of the cell membrane

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• Passive transport requires no energy from the
  cell, the energy comes from the difference in
  concentration not ATP (energy from the cell).
• Moves smaller substances from the higher to the
  lower concentration area.
• Important in transporting O2, CO2, water, small
  molecules.
• http//bcs.whfreeman.com/thelifewire/content/chp05
  /0502001.html

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Types of Passive Transport

• Diffusion moving substances within the cell and
  small nonpolar molecules across the phospholipid
  bilayer.

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• http//www.stolaf.edu/people/giannini/flashanimat/
  transport/osmosis.swf
• Osmosis the movement of water across the cell
  membrane by using the phospholipid bilayer or
  transport proteins.
• Tonicity
• Describes the tendency of a cell in a given
  solution to lose or gain water.
• Isotonic, hypertonic, and hypotonic

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Osmosis in action

• Isotonic solutions when cells are put into
  solutions that have equivalent salt
  concentration, visible osmosis does not take
  place.
• Hypotonic solutions Cells in very dilute
  solutions will take in water and eventually can
  burst (animal cells).
• Hypertonic solutions Cells in very concentrated
  solutions will lose water and shrink.

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http//bcs.whfreeman.com/thelifewire/content/chp05
/0502001.html

• Facilitated Diffusion a special type of
  diffusion in which the transported molecules are
  moved by the help of a transport protein.

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III. Active Transporthttp//bcs.whfreeman.com/the
lifewire/content/chp05/0502002.html

• Transport processes that can move substances from
  the lower concentration area to the higher by
  using energy.
• Energy is gained by using ATP molecules.

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• A type of active transport is the Na-K ion pump
• 3 sodium ions move out of the cell with the help
  of a transport protein, while 2 potassium ions
  move into the cell.

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IV. Bulk Transport

• Bulk transport transport through the cell
  membrane by using vesicles.
• Endocytosis a process by which large particles
  can move into the cell
• Types of endocytosis
• Phagocytosis engulfing solid particles
• Pinocytosis engulfing liquids, solutions
• Receptor-mediated endocytosis moving into the
  cell by first binding with receptor molecules on
  the cells surface.
• http//bcs.whfreeman.com/thelifewire8e/content/cat
  _010/0504003.html

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• Exocytosis the process by which the cell
  releases large molecules through its cell membrane