cellular transport · • cell transport: the movement of substances across the membrane of the...
TRANSCRIPT
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