Class Notes (810,487)
Canada (494,138)
Physiology (634)
PSL300H1 (220)

Lecture 1 - Sept 12 - Transport.docx

4 Pages
Unlock Document

University of Toronto St. George
William Mackay

Lecture 1 - Transport Sept. 12th, 2011 Cell Membrane - Permeable to gases, lipid-soluble molecules - Impermeable to orgaþnic anions (proteins) - Permeability of the membrane depends on molecular size, lipid solubility, and charge - Fatty acid tails help determine the properties - of the phospholipid Membrane Lipids - Polar end (head) is glycerol + phosphate (hydrophilic) + choline/serineOften charged - Nonpolar end is 2 long fatty acid chains (hydrophobic); one saturated, one polyunsaturated - Cholesterol is inserted among FA chains to stabilize the membrane + decrease permeability Membrane Fluidity - Determined by lipid composition - Necessary for efficient carrier and channel protein function - Cholesterol stabilizes membrane and prevents diffusion of polar molecules across it - Fluidity of a membrane is reduced by aging and a poor diet o Aging causes a loss of cholesterol  membrane can become leaky  Lack of unsaturated fats  Improper proportion of proteins, etc... Membrane Proteins - Structural support for cytoskeleton - Transmembrane channels for diffusion of molecules/ions - Selective transporters (carriers) of molecules across a membrane - Receptors for signalling molecules - Enzymes/ion pumps for active transport Membrane-Spanning Proteins - it is most common for a protein to cross the membrane 6-7 times - The part of the protein that crosses the membrane is usually helical - Carbohydrate chains (glycocalyx) Glycocalyx - Matrix of long carbohydrate filaments; they fill extracellular space, slowing diffusion 2+ - Net negative charge (polarized)  attract positive ions (Ca ) Membrane Permeability - If a substance can cross the membrane by any means, it is permeable to that substance - Gases can diffuse across the membrane - Polar molecules (water) and ions need the help of proteins (channels or carriers) to cross Lecture 1 - Transport Sept. 12th, 2011 Channels - 4-5 protein subunits fit together to create a central pore through the membrane - Pore loops formed by dangling parts of the protein molecule help create a selectivity filter to allow specific ions to filter through - S4 is usually charged (4 segment of the protein) Aquaporins - Family of channels specific for water + small non-ionic molecules (glycerol, urea) - Narrow part of this protein is about the size of a water molecule (~4 Angstroms) o Rate of diffusion is 3-5 times slower than regular passive diffusion o Chemical gradient drives the molecule through the pore Gated Channels - Channels can change shape to open/close - Factors determining channel protein shape: o Binding of chemical agent o Voltage across the membrane Image with potassium channel (voltage gated): - When polarized, the (–) charged side of the membrane attracts S4 (+) charged, causing the channel to close - When the membrane is depolarized, the S4 section returns to its original position, opening the gate Active Transport - Requires energy from ATP hydrolysis (using ATPases) (against the concentration gradient) - Substrate binds to protein carrier that changes conformation to move substrate across membrane ATPases (Examples) - Na -K pump - Ca pump - H pump (H -K ATPase) (found in stomach to make acidic environment) - Heavy metal pumps (Fe, Cu, Zn, Co) Sodium Pump (Na -K dependent ATPase) - 3 sites in cytosolic side of the protein o When 3 Na+ binds to their sites, ATP binds to the molecule + - When that ATP is broken to ADP + Pi, the protein changes shape, opening up a crevice to allow Na to diffuse through to the other side + - K from the extracel
More Less

Related notes for PSL300H1

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.