Class Notes (835,263)
Canada (509,050)
York University (35,229)
Biology (2,238)
BIOL 2021 (188)
Lecture

Ch. 11 - Membrane Transport of Small Molecules - Part 1 Summary of chapter and lecture on membrane transport of small molecules and electrical properties of membranes. Includes illustrations and graphics.

10 Pages
225 Views
Unlock Document

Department
Biology
Course
BIOL 2021
Professor
Julie Clark
Semester
Winter

Description
Biol 2021- March 17 2009- lecture Chapter 11 CHAPTER 11- Membrane transport of small molecules and electrical properties of membranes  The lipid bilayer of cell membranes prevents the passage of most polar molecules  This allows cell to maintain concentrations of solutes in its cytosol that differ from those in the extracellular fluid and in each of the inter cellular membrane enclosed compartments (domains).  Cells use specialized transmembrane proteins to transport inorganic ions and small water soluble organic molecules across the bilayer. Transmembrane transport proteins make up usually 15-30% of all membrane proteins in a cell  Cell membrane= permeability barrier  Small hydrophobic molecules and small uncharged polar molecules (slow rate) are able to diffuse through the membrane  Large uncharged polar molecules and ions cant diffuse through the membrane and require transport *membrane is highly impermeable to charged molecules (ions) no matter how small they are * In general the smaller the molecule and the more hydrophobic or non polar it is, the more rapidly it will diffuse across the membrane bilayer. Size of cargo Transport Mechanism - Small molecules: - Transport proteins  Ions, sugar - Marcomolecules: - Protein translocaters and  Proteins, RNA nuclear pores (chap 12) - Large particules - Endocytosis or phagocytosis  Other cells  Cell needs transport to: i. Ingest nutrients (glucose) ii. Excrete waste (urea) iii. Ion regulation - Plasma membrane (PM), internal membrane (IM)  Membrane transport proteins: transfer such solutes across cell membranes. > Each transport protein only transports specific type of molecule Two major classes of transport proteins: 1) Transporters: bind the specific solute to be transported and undergo a series of conformational changes to transfer the bound solute across the membrane.  CAN BE ACTIVE OR PASSIVE TRANSPORT 2) Channels: interact with the solute to be transported much more weakly. They form aqueous pores that extend across the lipid bilayer; when open, these pores allow specific solutes (usually inorganic ions of appropriate size and charge) to pass through them and thereby cross the membrane. Faster.  ALWAYS PASSIVE TRANSPORT AND ENERGY (panel 2-7) - Free energy: the total change in free energy during a set of reactions determines whether or not the entire reaction sequence can occur.  Enclosed system: collection of molecules that does not exchange matter with the rest of the universe. Any such system will contain molecules with a total energy E.  First law of thermodynamics: in any process, the total energy of the universe remains constant.  Second law of thermodynamics: the universe constantly changes so as to become more disordered. -h= ∆H= ∆E Entropy (∆S): randomness of molecules ∆S= h/T Gibbs Free Energy (G): Free energy change is a direct measure of the entropy change of the universe - Free energy of universe= free energy of cell + free energy of environment - G= H-TS - At constant temperature : -∆G= -∆H + T∆S  At equilibrium ∆G= 0 (only dead cells)  We are burning up energy and changing environment or universe by being alive ION CONCENTRATIONS - Table 11-1 is important - Ion gradients across membrane creates membrane potential  Voltage across membrane (-20mV to -150 mV)  - means negative inside cell Electrochemical gradient - Electrical= charge difference - Chemical = concentration difference Electrical (how much energy does it take to push ion across membrane) ∆G= Zfv z= charge on ion F= faradays constant V= voltage ~ membrane potential Chemical ∆G= -RTln (concentration outside/concentration inside) R: gas constant T: temp in cells is constant Electrical + chemical = amount of energy required for ion to go across membrane PASSIVE TRANSPORT (FACILITATED DIFFUSION)  Transporters that allow solutes to cross the membrane only passively  For a neutral molecule, passive transport occurs down a concentration gradient (high concentration to low concentration)- the concentration gradient will determine the direction of transport.  For a charged molecules, electrochemical gradient and concentration gradient influence transport (electrochemical gradient- combination of both gradients)  Inside of cell is usually negative  Mediated channels are always passive ACTIVE TRANSPORT  Proteins actively pump certain solutes across the membrane against their electrochemical gradients; is mediated by transporters, which are called pumps.  Coupled with an energy source ie. ATP, light, ion gradient  Coupling to an energy source creates a gradient MEMBRANE TRANSPORT PROTEINS - Transport proteins do not modify the solute it transports - Transport proteins have multiple binding sites for its solute - The binding site can be blocked by competitive inhibitors or non competitive inhibitors (bind elsewhere and specifically alter the structure of the transporter)  General properties of transport proteins: 1) Multipass transmembrane: goes many times through membrane 2) Specific for certain molecule (like enzyme specificity) 3) Role of transport saturates at increasing concentration  Similar to enzyme saturation kinetics  Diffusion through membrane: no saturation; increase concentration= increased rate  Vmax: max rate  Km: binding constant 4) Can be inhinited by small molecule inhibitors - Transporters undergo reversible conformational change during transport- expose solute binding site first on one side of the membrane and then on the other - Channel (firm pore): doesn’t undergo conformational change; uses selectivity filter  In transporter (figure 11-5): affinity for substrate binding is higher on outside of cell and lower on inside  Flipping randomly for transport  For passive transport: down concentration gradient; probability  Movement doesn’t stop when ion concentrations become equal  For active transport energy sources are needed  For passive transport, electrochemical gradient is the energy source Cells carry out active transport in three main ways: I. Coupled transporters: couple the uphill transport of one so
More Less

Related notes for BIOL 2021

Log In


OR

Join OneClass

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

Sign up

Join to view


OR

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.


Submit