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