Lecture 7 - Membrane Transport - Unassisted.docx

Lecture 7: Membrane Transport: Unassisted Membrane Transport Tonicity vs. Osmolarity - **Tonicity:** the effect the solution has on cell volume. - Only refers to non-penetrating solute - Determined by the concentration of the solution in non-penetrating solutes -...

Lecture 7: Membrane Transport: Unassisted Membrane Transport Tonicity vs. Osmolarity - **Tonicity:** the effect the solution has on cell volume. - Only refers to non-penetrating solute - Determined by the concentration of the solution in non-penetrating solutes - Non-penetrating solute: Solute that does not permeate plasma membrane. - **Isotonic solutions:** result in a constant cell volume. - **Hypotonic solutions:** tend to *swell* the cell. - **Hypertonic solutions:** tend to *shrink* the cell. Osmolarity: the measure of solute concentration per unit volume of solvent. - not the same as Tonicity! - Osmolarity = Non-penetrating + Penetrating - Takes into account all solute concentrations; penetrating and non-penetrating solutes) - ISO-osmotic: Osmolarity = penetrating solution amount - Hypo-osmotic: Osmolarity \< penetrating solution amount - Hyper-osmotic = Osmolarity \> penetrating solution amount Ion forming compounds = Osmolarity \> Solutions molarity - NaCl when dropped in water will split and double - So if a NaCl concentration of 200 mmol/L is dropped into a solution, it will split into Na+ 200mosmol/L and Cl- 200 mosmol/L = total of 400 mosmol - Molarity remains the same (200mmol) Membrane Transport: Assisted Membrane Transport How do large, poorly lipid-soluble molecules cross the Plasma Membrane? 1. Carrier Mediated Transport Function: - For transport of small water soluble molecules. - Can reverse shape so binding sites are alternately exposed to ECF and ICF. - Span the plasma membrane. 3 Important Characteristic that affect Fick's Law of Concentration Gradient: - Specificity (amino acids cannot bind to glucose carriers) - Saturation (limited number of carrier binding sites) - Competition (closely related compounds compete for access) Facilitated Diffusion: Uses a carrier molecule to facilitate (assist) the transfer of a substance across the membrane from high to low concentration. - Passive Transport - so it doesn't require energy - Occurs naturally down a concentration gradient - Saturation (if there is a lot) limits the rate of carrier binding sites - Glucose transported into cells from blood stream via Glucose. Transporters