Cellular Transport

• Cell transport: the movement of substances across the membrane of the cell

• Allows a cell to take in and release substances in accordance with its function

• Regulation of substances found in, or secreted by cells at specific times

• Cells have to import needed substances into the cell and eliminate waste materials from the cell and also secrete substances to communicatewith other cells

• Substances = ions and molecules

Cell Membrane • Selectively permeable: only certain substances transported in or out

• Fluid Mosaic Model

– Composed of phospholipids and proteins

– Phospholipid bilayer

• Phospholipid heads that are hydrophilic and point toward the outside

• Fatty acid tails that are hydrophobic and point toward the inside

– Proteins embedded within the cell membrane:

• Carrier (molecules) and channel (ions) proteins

• Integral and peripheral proteins

– Cholesterol for stability

– Carbohydrates attached to lipids or proteins

• Allows some materials to easily pass through the membrane

• Polarity and size prevent molecules from passing

– Large molecules and ions require assistance to pass

Cell Membrane

Passive Transport

• Does not require energy

• Three types

– Diffusion

– Osmosis

– Facilitated diffusion

• Carrier proteins

• Channel proteins

Diffusion

• The movement of molecules from an area of high concentration to lowconcentration

• Medium-sized, non-polar solutes can pass through the membrane

• Ends once the molecules are evenly dispersed between the internal and external environment – dynamic equilibrium has been achieved

• Brownian motion (random movement of fluid particles) is always happening

Osmosis

• The movement of water molecules from an area of low to high solute concentration

• Balances solute concentrations on both sides of the cell membrane

• Isotonic solution: when the solute concentration of two solutions on either side of a membrane are equal

Osmosis: Solute Concentration

• Hypotonic solution: when the solute concentration is lower on the outside and higher on the inside of the cell

Osmosis: Solute Concentration

• Hypertonic solution: when the solute concentration is higher on the outside of the cell and lower on the inside

Osmosis: Solute Concentration

Facilitated Diffusion

• The movement of materials from an area of high to lowconcentration without the use of energy using a membrane

• Channel proteins for ions

• Carrier protein for molecules that can’t pass through the membrane

Channel Proteins

• Allow the passage of ions across the cell membrane

• Custom fit to each ion’s size and charge

• Some are gated (they can open and close)

Carrier Proteins

• Allows the passage of a specific type of molecule based on it’s: size and shape

• Involve a conformational change to facilitate the diffusion

Active Transport

• The movement of materials against the concentration

gradient, from an area of low concentration to high

concentration

• Uses energy provided by the cell (e.g. ATP)

• Movement using protein pumps

• The sodium-potassium pump• 3 sodium ions in and 2 potassium ions out!

The Sodium-Potassium Pump

• Both sodium and potassium ions are moving from areas of low concentration to areas of high concentration

• Ions are moving against the concentration gradient

• ATP provides the energy to change the shape of the channel

• One phosphate group from the ATP remains bound to the channel until potassium binds