Active Transport Topics 2.6 and 2.9 Active Transport Overview - PowerPoint PPT Presentation

Active Transport Topics 2.6 and 2.9

Active Transport Overview • Requires free energy (ATP) to move molecules

Active Transport: Membrane Pumps • Uses membrane proteins embedded in the membrane to move solutes against their gradients • Allows cells to maintain concentration gradients that differ from their surroundings • Some pumps establish and maintain membrane potentials (voltage) • Examples: sodium-potassium pump, proton pump

Factors Affecting Cellular Transport • Chemical driving force • Electrical driving force • Electrochemical driving force (combination)

Sodium-Potassium Pump (video link – please watch – 2:26) • Pumps sodium ions (Na + ) out of the cell and potassium ions (K + ) into the cell • Regulates osmolarity of cytosol by controlling the solute concentration inside the cell • Maintains and restores the resting potential of cells, such as neurons, cardiac and kidney • Primary pump in animal cells

Nerve Cell Signaling (video link – please watch – 2:52)

Proton Pump (video link – please watch – 1:04) • Moves protons (H + ) against the concentration gradient in order to generate a proton gradient across the membrane • Used in the synthesis of ATP during cellular respiration • Causes changes in pH

Active Transport: Bulk Transport • Involves changes in the membrane structure • Transports macromolecules (proteins, polysaccharides, etc.) by packaging the materials into vesicles

Exocytosis • Cell secretes large molecules by fusion of the vesicles with the cell membrane

Exocytosis Example • Release of neurotransmitters between neurons

Endocytosis • Region of the cell membrane sinks inward and pinches off to form a vesicle to bring extracellular material into the cell

Endocytosis: Phagocytosis • Cells engulf large particles or other cells using pseudopods • Example: white blood cell consuming bacteria, ameba consuming food

Endocytosis: Pinocytosis • Droplets of extracellular fluid are taken into the cell in small vesicles • Example: Uptake of nutrients by the microvilli of the small intestine

Receptor-Mediated Endocytosis • Enables cells to acquire specific substances from extracellular fluid • Molecules bind to receptors • Example: cholesterol uptake from the blood

Review of Cellular Transport (video link – please watch – 4:44)