Lecture 2 Membrane transport processes

Lecture 2 Membrane transport processes - Introductory...

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Introductory Physiology PCM 4713C G. A. Ahearn Lecture 2: Membrane transport processes
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Membrane transport processes Solute characteristics that affect membrane transfer 1. Species of molecule 2. Molecular size 3. Lipid solubility 4. Charge 5. Polarity 6. Degree of ionization pid solubility Partition coefficient defines lipid solubility: P.C. = solute solubility in oil/solute solubility in water The higher the P.C. the greater the permeability of solute in membrane. Addition of methyl and ethyl groups to urea increase the permeability of compound in spite of an increase in size.
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Effect of solute partition coefficient on membrane permeability
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Polarity The degree of polarity of a solute will affect its partition coefficient and permeability. a. Non-polar compounds : electrons shared equally by 2 atoms making up a bond between them. Example: Cl 2 (chlorine gas). High partition coef. and high permeability. + Cl e- e- + Cl b. Polar compounds: electrons of one atom attracts more electrons than the other. Example: Iodine chloride. Low partition coefficent and low permeability. + Cl I 2e- +
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Molecular weight The greater the molecular weight, the larger the molecule and the slower it will cross a membrane. Log molecular weight Log diffusion rate Degree of ionization 1. An increase in charge, slows rate of diffusion. 2. Cations: Na + > Ca 2+ > Fe 3+ 3. Anions: Cl- > SO 4 2- > PO 4 3-
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Transport mechanisms across membranes Passive transport mechanisms Passive transport relies on a greater concentration of solute on one side of membrane than the other. The concentration gradient becomes the “driving force” for passive transport across the membrane down the concentration gradient. 1.
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Lecture 2 Membrane transport processes - Introductory...

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