2.4 - Transport Across Membranes

• Cells need to transport materials in and out of the cell to survive.

  • Waste needs to be removed
  • Nutrients need to enter the cell
  • Cells need to communicate through chemicals
• Some materials enter passively (no energy) while others need to be transported actively (using energy)
• Passive Transport - the movement of substances from an area of high concentration to an area of low concentration without the use of energy
• What drives passive transport?

  Diffusion
• Why Transport?

  Wastes need to be removed

  Nutrients need to enter the cell

  Cells need to communicate through chemicals
• What are the two types of Passive Transport?

  Simple Diffusion & Facilitated Diffusion
• Simple Diffusion - movement of small/non-polar substances across the membrane without using energy

  • e.g. CO2 and O2 move freely across membranes
• Smaller substances move faster than larger substances
• Facilitated Diffusion - the movement of molecules across a membrane with the help of a protein
• Facilitated Diffusion uses transport proteins which provide pathways for molecules to pass through
• Chanel Protein - hydrophilic pathway through membrane
• Carrier Protein - physically binds to molecules to aid in transportation
• What type of protein is this? What does it do?

  Chanel Protein

  • used to transport certain ions (ex. Na+, K+, Cl-)
  • Involved in nerve signals

  
• What type of protein is this? What does it do?

  Carrier Proteins

  • Bind to specific substances (ex. amino acids)
  • Changes shape to help transport substances

  
• Osmosis - the passive diffusion of water across membrane
• Osmosis always moves from an area of lower solute concentration (high water content) to an area of higher solute concentration (low water content)
• What determines water movement?

  Solute Concentration (dissolved substances)
• The concentration of solutes around cells determines their shape
• Hypertonic Solution - high concentration of solutes outside cell = water rushes OUT of cell
• Hypotonic Solution - low concentration of solutes outside cell = water rushes INTO cell
• Isotonic Solution - equal concentrations of solutes inside/outside cell = no net gain or loss of water
• What type of solute concentration is this?

  Isotonic solution (normal)

  
• What type of solute concentration is this?

  Hypotonic solution (diluted)

  
• What type of solute concentration is this?

  Hypertonic solution (concentrated)

  
• What is active transport?

  The movement of substances across membrane using energy

  • movement is AGAINST the concentration gradient
  • uses ATP to “pump” substances across
• Primary Active Transport - moves POSITIVELY CHARGED IONS across the membrane

  • generally relies on energy (ATP)
  • helps establish electrochemical gradients which are important in nerve functioning
• Secondary Active Transport - uses energy from the concentration gradient built up by primary active transport to transport substances
• Symport - transported substances move in the SAME DIRECTION as ions
• Antiport - transported substances move in the OPPOSITE DIRECTION as ions
• What type of transport is this?

  Uniport (passive - no ATP) - transport of a single molecule in single direction

  
• What type of secondary active transport is this?

  Symport - transported substances move in the SAME DIRECTION as ions

  
• What type of secondary active transport is this?

  Antiport - transported substances move in the OPPOSITE DIRECTION as ions

  
• How does primary active transport work?

  By using energy (ATP)
• How does secondary active transport work?

  by using ion gradients as driving force
• Exocytosis - transport of substance from inside of cell to outside of cell using vesicles
• Why is exocytosis needed?

  To transport substances larger than amino acids/monosaccharides
• Endocytosis transports substances outside the cell in three ways: pinocytosis, receptor-mediated endocytosis, and phagocytosis
• What is this layer called?

  Semipermeable membrane

  
• Pinocytosis (cell drinking) - brings in fluid along with any molecules within fluid
• Receptor- mediated Endocytosis - molecules bind to receptor proteins on outer surface before coming into cell