Chapter 3 - Membrane Transport (Part 3)
Two Types of Membrane Transport - moving substance in and out of cell
- Passive (Physical) Process - requires no cellular energy
- Active (Physiological) Processes - requires cellular energy in the form of ATP
- Passive Transport - nonpolar and lipid-soluble substances
- Diffuse directly through the lipid bilayer - simple diffusion & osmosis
- Diffuse through channel proteins and facilitated diffusion
- Simple diffusion - the tendency for solute molecules to move from an area of high concentration to an area of low concentration
- Caused by - Random Motion
- Rate of diffusion depends on
- Concentration gradient
- Temperature
- Viscosity
- Size of solute
- Channel Proteins and Facilitated Diffusion
- Transport maximum is the upper limit on the rate at which facilitated diffusion can occur. If all the transporters are occupied, then the rate of facilitated diffusion does not increase.
- Facilitated Diffusion of Glucose
- Glucose binds to transport protein
- Transport protein changes shape
- Glucose moves across cell membrane (but only down the concentration gradient)
- Kinase enzyme reduces glucose concentration inside the cell by transforming glucose into glucose-6-phosphate
- Transporter proteins always bring glucose into cell
- Channel Proteins - transports small polar molecules (size specific)
- Osmosis the diffusion of water through a selectively permeable membrane
- water moves toward a higher concentration of solutes
- Osmolarity - total concentration of solute particles in a solution
- Tonicity - how a solution affects cell volume
- Isotonic solution = 0.9% Na Cl (physiological saline)
- Hypertonic solution >physiological saline
- Direction water moves?
- Effect on cell?
- Hypotonic solution < 0.9% NaCl
- Direction water moves?
- Effect on cell?
- Filtration - uses a pressure gradient which forces molecules through holes in a membrane or blood flow.
- Kidney filters the blood due to blood pressure
- Hydrostatic (BP) from high to low
- Active Membrane Transport
- requires cellular energy (ATP) to go against the concentration gradient
- Membrane carrier proteins act as "pumps"
- Secondary Active Transport
- In secondary active transport, the energy stored in the form of a sodium or hydrogen ion concentration gradient is used to drive other substances against their own concentration gradients.
- Plasma membranes contain several antiporters and symporters powered by the sodium ion gradient.
- Digitalis
- Digitalis slows the sodium ion-calcium ion antiporters, allowing more calcium to stay inside heart muscle cells, which increases the force of their contraction and thus strengthens the heartbeat.
- Vesicular Transport
- Transport of large particles and macromolecules across plasma membranes
- Endocytosis - enables large particles and macromolecules to enter the cell
- Phagocytosis - pseudopods engulf solids and bring them into cell's interior
- Receptor-mediated endocytosis - clathrin-coated pits provide the main route for endocytosis and transcytosis (intake of insulin and cholesterol)
- Exocytosis - moves substance from the cell interior to the extracellular space
- Transcytosis - endocytosis followed by exocytosis.
- Vesicular trafficking - moving substances from one area in the cell to another
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