 You must have lab ready for tomorrow  Lecture #6

 Take in nutrients  Expel waste  Communicate with it’s environment  Communicate with neighbouring cells

 The plasma membrane must be highly selective  It must be able to take in a very large food molecule while preventing very small and valuable molecules from leaving the cell  It must recognize and block harmful foreign substances while expelling the cell’s toxic waste products

 Membranes within the cell must also be crossed by important materials  Ex. in the mitochondria and chloroplasts reactions occur which require reactants from outside the organelle and produce products that need to leave

 The movement of a substance across a membrane without the need use energy  Diffusion is the main type of passive transport  Diffusion is the movement of molecules from a place of higher concentration to a place of lower concentration  The rate of diffusion depends on the concentration difference (aka concentration gradient) between the two areas

1. Simple Diffusion: the ability of substances to move across a membrane unassisted (ex. Water, Oxygen and Carbon Dioxide) 2. Facilitated Diffusion: when substances require help by transport proteins to cross a membrane (ex. Sugars or amino acids), though this is still based on concentration gradient

1. Channel Proteins: a hydrophilic pathway in a membrane that enables water and ions (ex. sodium, potassium, calcium and chloride) to pass through

2. Carrier Proteins: bind to a specific solute (ex. glucose molecule or particular amino acid) and transports it by changing shape to move it across the lipid bilayer. *Each protein is VERY specific (one for glucose could not transport fructose) which means SUPER tight control

 Diffusion of water across a membrane  In living cells this movement can cause swelling and shrinking depending on the cell’s surrounding conditions  There are three kinds of surrounding conditions (hypotonic, hypertonic and isotonic) and each impacts the cell in a different way

1. Hypotonic: a solution that has a lower solute concentration than another (water moves into the cell) 2. Isotonic: a solution that has the same solute concentration than another (the cell remains unchanged) 3. Hypertonic: a solution that has a higher solute concentration than another (water moves out of the cell)

 The movement of substances across membranes against their concentration gradient using pumps  Energy-dependent (about 25% of a cell’s energy requirements are used for active transport)  Classified as either primary or secondary active transport

 Use transport pumps  ONLY move specific positively charged ions (ex. hydrogen)  A hydrogen pump (aka proton pump)in the plasma membrane pushes hydrogen ions form the cytosol to the cell exterior  The pump will bind to a phosphate group from ATP to provide the energy to move the ion

 Uses the concentration gradient of an ion as it’s energy source  Facilitated by two mechanisms – symport and antiport  Symport: a solute moves through the membrane channel in the same direction as the driving ion  Antiport: the driving ion moves through the membrane channel in one direction, providing energy for the transport of another molecule in the opposite direction