1 Membrane transport and potential

1 Membrane transport and potential - MEMBRANE TRANSPORT &...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
MEMBRANE TRANSPORT & MEMBRANE POTENTIAL AC Brown page 1 A7a INTRODUCTION A. Intracellular and Interstitial Distribution 1. Concentrations of dissolved substances Example: Mammalian Nerve or Skeletal Muscle Cell Interstitial Intracellular Na + (Sodium ion) 145 10 mM/l (millimoles/liter) Cl - (Chloride ion) 110 5.5 mM/l K + (Potassium ion) 5 155 mM/l Protein - 1 35 g/dl (grams/100 ml) Glucose 5 (90) Low mM/l (mg/dl, milligrams/100 ml) 2. Electrical charges Inside of the cell is generally negative relative to the outside of the cell Intracellular electrical potential (V m ) typically -70 to -80 millivolts (mV) 3. Unexpected, because concentration and electrical gradients would be expected to dissipate spontaneously 4. Concentration and electrical differences associated with cell vitality -------- Intracellular fluid: fluid within the cell (ICF); part of the cytoplasm Interstitial fluid: fluid in the interstitial space surrounding the cell (part of "extracellular" fluid (ECF); generally similar to blood plasma except less plasma protein)
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
MEMBRANE TRANSPORT & MEMBRANE POTENTIAL AC Brown page 2 A7a RATE OF MEMBRANE MOVEMENT A. Major Factors TRANSPORT RATE = AREA x PERMEABILITY x NET DRIVING FORCE B. Area (A) 1. Define: Area available for transport across cell wall or organ surface C. Permeability (P) 1. Define: ease with which a particular particle passes through the membrane example: P Na+ = Sodium ion permeability NOTE: For the common monovalent ions Na + , K + , and Cl - , the relative permeabilities in resting mammalian nerve and skeletal muscle cells are P K P Cl >> P Na D. Net Driving Force 1. Sum of passive forces (such as diffusion and electric forces) and active forces requiring energy developed by living systems (more later) MODES OF MEMBRANE TRANSPORT A. Cell Membrane Structure 1. Phospholipid bilayer Note: Lipid core is impermeable to charged particles (ions) and polar substances 2. Proteins, including membrane-spanning proteins (integral proteins or transmembrane proteins) which can aid in membrane transport 3. Carbohydrates, associated with membrane proteins (glycoprotein) or membrane lipids (glycolipid) 4. Cholesterol (membrane flexibility)
Background image of page 2
MEMBRANE TRANSPORT & MEMBRANE POTENTIAL AC Brown page 3 A7a MODES OF MEMBRANE TRANSPORT (continued) B. Dissolve in Membrane Lipid 1. Only applicable to lipid-soluble substances 2. Permeability depends on degree of lipid solubility (sometimes measured by oil-water partition coefficient) 3. Substances utilizing this mechanism include a. small, lipid-soluble organic molecules b. dissolved gases (O 2 , CO 2 , etc.) c. water (!) C. Simple, Passive Movement Through Channels 1. Channel: membrane-spanning macromolecule with an aqueous pore in its center 2. Aqueous-soluble particles can move through pores (charged particles and polar particles) 3. Some channels are selective for one or a small group of substances (e.g. Na- channel, K-channel); some channels are non-selective (e.g. “leak” channel)
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/03/2012 for the course BIO 308 taught by Professor Acbrown during the Spring '10 term at Portland.

Page1 / 9

1 Membrane transport and potential - MEMBRANE TRANSPORT &...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online