You must have lab ready for tomorrow Lecture #6

Take in nutrientsExpel wasteCommunicate 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