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Unformatted text preview: Membrane Transport 1: Diffusion vs Active Bio 106 Fall 2009 Professor Owen True or False? Margarine contains more saturated lipids than the vegetable oil from which it is made.
A. B. C. True False Not sure Membrane Transport
How do molecules move across membranes? Background
• Membrane = selectively permeable
– barrier to the passage of most polar molecules due to hydrophobic interior – cell needs to retain essential molecules cell needs to retain essential molecules within within compartments, while allowing other molecules to enter and leave Freely Permeable Molecules
Some examples: • Hydrophobic molecules
– O2, N2, benzene benzene • Small uncharged molecules
– CO2, ethanol, urea – water (somewhat freely crosses…) • A few molecules move across the membrane unrestricted = permeable Membrane Permeability Impermeable Molecules
Many molecules are essentially impermeable
(or so slow to be effectively impermeable to crossing the membrane) 1. Large molecules of any kind 2. Charged polar molecules 3. Ions Cooper 13.15 Lecture 7 1 Membrane Transport 1: Diffusion vs Active Bio 106 Fall 2009 Professor Owen Factors That Affect Membrane Permeability
1. Thickness of the membrane 2. Fluidity of the membrane
– more fluid = more permeable Diffusion
diffusion is the movement of a substance from a region of high to low concentration = molecules move “with the concentration gradient gradient” 3. Proteins
– Proteins can help move molecules across the membrane • Happens spontaneously • Requires NO energy • Two types of diffusion
1. Simple passive diffusion 2. Passive transport Simple Passive Diffusion
• No energy required; no protein used • Substance moves across the membrane from high to low concentration, with the with gradient
– moves towards equilibrium • movement = known as flux • into = influx • out of = efflux
– Special example: water diffusion = osmosis Which of the following is the best definition of diffusion? A. Molecules move against the concentration gradient using energy B. Molecules move with the concentration gradient using energy C. Molecules move with the concentration gradient using no energy D. Molecules move against the concentration gradient using no energy A Different Type of Diffusion Passive Transport
• Uses membrane proteins
• No energy required • Can only move molecules with the concentration gradient
(therefore (therefore diffusion) Passive Transport Passive Transport (Facilitated (Facilitated Diffusion) • Two types
– Transporter – Channel Lecture 7 2 Membrane Transport 1: Diffusion vs Active Bio 106 Fall 2009 Professor Owen Transporter Proteins For Passive Transport
• Carrier protein binds to ion or molecule • Highly specific • Faster transport than simple diffusion but becomes saturated • Involves a transport protein that acts like an enzyme in terms of kinetics
– therefore has a Km and Vmax Simple diffusion and passive transport are similar in that they both move ______ but different because _________. A. molecules WITH the concentration gradient; passive transport uses carrier proteins B. molecules AGAINST the concentration AGAINST the concentration gradient; passive transport uses carrier proteins C. molecules WITH the concentration gradient; simple diffusion uses carrier proteins D. molecules WITH the concentration gradient; passive transport requires energy Passive (Facilitated) Transport Transport (Carrier) Protein Hypothetical model showing how a conformational change in the protein could transport a solute with the concentration gradient.
Lodish 15-5 Movie 12.3 ECB3 12-6 What is the result of moving ions across membranes? Why move molecules from Why move molecules from one one side to another? Ion Concentrations in Cells
Example: typical vertebrate cell Note the large concentration differences between inside and outside the cell. Cooper 13.29 Lecture 7 3 Membrane Transport 1: Diffusion vs Active Bio 106 Fall 2009 Professor Owen Movement of Ions
• Cells maintain an asymmetric ion balance across membranes • Move the ions in two ways: 1. Pumps (active transport) (active
• movement against the concentration gradient • requires energy Comparison of Passive and Active Transport 2. Ion channels (diffusion) (diffusion
• Channel – typically “gated” (requires a stimulus to open)
ECB3 12-4 Active Transport
Three types of active transport: 1. Primary active transport
• ATP-driven pump Animation 12.1 Approximately 1/3 of the energy requirements of a typical animal cell is used by this pump Na+/K+ ATPase 2. Co-transport carriers Co3. Light-driven pump Light pump Energy source Exterior 3 Electrochemical gradient • movement driven by ion gradients 3Na+ P Against Conc. Gradient ECB3 12-8 Cytoplasm 2
Modified from ECB3 12-9 Na+ - K+ Pump – Action in a Series of Steps Na Na+-K+ Pump Maintains Osmotic Balance of Animal Cells
ECB3 12-12 osmosis Cooper 13.28 Animation 12.1 ECB Movie 12.1 Lecture 7 4 Membrane Transport 1: Diffusion vs Active Bio 106 Fall 2009 Professor Owen Ca++ ATPase Electrochemical Gradient ECB3 12-15 [Ca2+ ] is kept very low in the cytosol Greatest energy potential ECB2 12-8 GlucoseGlucose-Na+ Symport Protein ECB3 12-17 Movement of glucose against its concentration gradient. Lecture 7 5 ...
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This note was uploaded on 03/03/2011 for the course BIO 106 taught by Professor T.pageowen during the Spring '11 term at Conn College.
- Spring '11
- molecular biology