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46 Cards in this Set

  • Front
  • Back
Cell membranes are primarily composed of:
-Phospholipids
-Proteins
(some cholesterol)
What is the structure of phospholipids that make up the lipid bilayer?
-Glycerol backbone (hydrophilic)
-2 Fatty acid tails (hydrophobic)
What are 3 lipid soluble substances that can cross the cell membrane because they dissolve in the hydrophobic lipid bilayer?
-Oxygen
-Carbon dioxide
-Steroid hormones
What are 4 water soluble substances that can't cross the cell membrane?
-Sodium
-Chloride
-Glucose
-Water
How can water-soluble substances cross the cell membrane?
-Water filled channels
-Pores
-Carrier transport
What are 2 types of proteins that may be found in the cell membrane?
-Integral
-Peripheral
How are integral proteins situated in the membrane? How are they anchored?
-Span the entire membrane
-Anchored by hydrophobic interactions with the bilayer
What are 2 examples of integral proteins?
-Ion channels
-Transport proteins
How are peripheral proteins situated in the membrane?
-On either the intra or extracellular surface of it
What is an example of a peripheral protein?
Hormone receptors
What are 2 types of intercellular connections between membranes?
-Tight junctions
-Gap junctions
What cells are often connected by tight junctions? What is another name for tight junctions?
Epithelial cells
-Aka zonula occludens
What are 2 forms of tight junctions that can be found in the body? Where?
TIGHT tight junctions - in the distal renal tubule
LEAKY tight junctions - in the proximal renal tubule or gallbladder
What is the function of gap junctions?
Intercellular communication
What is a great example of tissue that has gap junctions between its functional cells?
Myocardium
4 Types of transport across cell membranes:
1. Simple diffusion
2. Facilitated diffusion
3. Primary active transport
4. Secondary active transport
What is the ONLY form of transport that is not carrier mediated?
Simple diffusion
How come simple diffusion does not require a carrier?
Because it occurs DOWN an electrochemical gradient.
What law describes and calculates simple diffusion?
Fick's law
What is Fick's law?
(Flux) J = -PA(C1-C2)
What do C1 and C2 represent?
What is A?
What is P?
C1 = the higher concentration
C2 = the lower conc
A = the surface area for diffusion
P = the permeability coefficient
What does the permeability coefficient represent?
The mobility of a substance in the membrane
What is the major determinant of the permeability coefficient and hence drug mobility?
The lipid:aqueous partition coefficient
What does the partition coefficient reflect?
How easily a drug enters the lipid phase from the aqueous medium
So what will a drug with a high partition coefficient be?
Hydrophobic - preferentially dissolved in the lipid bilayer
What will a drug with a low partition coefficient be?
Hydrophilic - preferentially dissolved in serum/blood.
1 ml =
1 cm cubed
3 factors that increase the permeability coefficient for a substnace:
-Increasing partition coefficient (lipid:aqueous)
-Decreasing radius/size of solute
-Decreasing membrane thickness
What features of molecules give the highest permeability in membrane lipid bilayer?
-Small
-Hydrophobic
What is required for hydrophilic solutes to cross the membrane?
-Water filled channels
-Pores
What type of solutes cross independently of the electrical potential difference across a membrane?
Noncharged solutes
What are the 3 types of carrier mediated transport across membranes?
-Facilitated diffusion
-Primary active transport
-Secondary active transport
3 important characteristics of carrier-mediated transport:
-Stereospecificity
-Saturation
-Competition
What is a good example of stereospecificity of carrier-mediated transport?
The natural isomer of glucose, D, is carried by the membrane transporter; not l-glucose
What is Tm?
The transport max of a carrier for membrane transport; analogous to the Vmax of an enzyme
What is a competitive inhibitor of glucose transport in the small intestine?
Galactose
What is facilitated diffusion similar to? What makes it unique from active transport?
-Similar to passive diffusion - occurs downhill
-Passive; Does not require energy
How is facilitated diffusion DIFFERENT from simple diffusion?
-Carrier mediated
-It's FASTER than simple!
What is the physiological example of facilitated diffusion?
Uptake of glucose in muscle and fat cells
What sugar inhibits glucose uptake in muscle/fat?
Galactose
What is required for the carriers to facilitate glucose diffusion in muscle/fat cells?
Insulin
What are the 3 main features of primary active transport?
-Uphill
-Requires direct ATP input
-Carrier mediated
3 examples of primary active transport:
-Sodium/potassium ATPase
-Calcium ATPase
-H/K ATPase
What direction and how many ions of sodium/potassium are transported by the ATPase?
-3 sodiums go from intra to extracellular
-2 potassiums go from extra to intracellular
What does the N/K ATPase maintain in cells?
-High cellular potassium
-Low cellular sodium
Is the transport of either Na or K by the ATPase easy (downhill)?
No; both go against their gradient