PCL201H1 Lecture 8: Lecture 8 Absorption Mechanisms

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azuresquirrel208

11 Apr 2012

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Aquaporin channels: most allow only water but a-3 allows small water soluble molecules, pore width ~8-10 angstroms, therefore allows hydrophilic molecules <200da passage, only small molecules, diffusion, high concentration to low concentration via passive diffusion. Remember compounds that are hydrophilic have low pow. Increased molecular size, decreased permeation rate (ability of molecule to cross membrane) Lipid soluble drugs diffuse across lipid molecules of membrane. Rate of diffusion depends on: concentration of drug, pow, degree of ionization, surface area of membrane (stomach vs. small intestine) Concentration of drug and the diffusion across the membrane is not always linear: major issue with regulating drug dosage, can not always assume linear relationship. Role of pow partition coefficient major factor with regards to drug absorption. Ideally the higher pow the more rapidly absorbed. Review: optimum value for drug abosprtion due to hydrophilic barrier associated with glycocalyx: cut off phenomenon: very lipophillic reduced absorption unable to cross stagnant water layer.

Related Questions

11. Synthesis of ATP using the energy released as a proton diffuses down a concentration gradient involves the conversion of concentration gradient energy into chemical energyâTrue or false?

12. In the absence of active transport of a molecule, a simple or facilitated diffusion of the molecule will result in an equilibrium of the molecule across the membraneâTrue or false?

13. In the absence of an active transport of a molecule, a simple or facilitated diffusion of the molecule across a membrane will result in zero energy available to do workâTrue or false?

14. If biological membranes were permeable to all solutes osmosis could not occur because the concentration of water will be same on both sides of the membraneâTrue or false?

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1. To move molecules from a low concentration on one side of amembrane to a high concentration on the other side of a membrane,which would be needed?
A.
Time
B.
A protein that can engage in facilitated diffusion
C.
An active (energy-requiring) process that moves the moleculesdirectly rather than relying on diffusion

Answer choice c

2. If a cell transports a number of these ions across the membrane,which direction of transport would require energy from thecell?
A.
From the outside to the inside of the cell
B.
From the inside to the outside of the cell

Answer choice A

3. Which of the following is not true of the carrier moleculesinvolved in
facilitated diffusion?

A.
They do not require energy to operate.
B.
They can concentrate molecules on one side of the membrane.
C.
They allow molecules to travel both directions across amembrane.
D.
They may undergo a structural (conformational) change upon bindinga molecule.

Answer choice D

match each condition to its effect on diffusion rate; Increases Rate of Diffusion or Decrease Rate of Diffusion

a) Increased membrane permeability

b) Increased temperature

c) approaching diffusional equilibrium

d) destruction of alveoli in the lungs due to emphysema

e) increased membrane surface area

f) Villi and microvilli in the intestinal epithelium

g) increased synthesis of channel proteins

h) decreased cell height, creating a flatter cell

i) decreased molecular weight

j) decreased concentration gradient

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PCL201H1 Lecture 8: Lecture 8 Absorption Mechanisms

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