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36 Cards in this Set
- Front
- Back
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What is a phospholipid molecule? |
a glycerol backbone with 2 long-chain fatty acids esterfied to the 1st and 2nd carbons and phosphoric acid esterified to the 3rd carbon of glycerol |
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what is responsible for the barrier properties of membranes? |
Fatty acid tails of membrane phospholipids |
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Amphipathic |
hydrophilic and hydrophobic properties |
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Orientation of phospholipid in the lipid bilayer? |
glycerol backbone dissolves in the H2O fatty acid tails dissolve in the oil phase |
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Barrier properties of lipid bilayer? |
1. H2O soluble solutes are excluded (polar {sugars, amino acids} or charged solutes) 2. Permeable to lipid soluble substances (CO2, O2, NO, steroid hormones, and some drugs) and small uncharged polar molecules (H2O, urea, glycerol) |
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Integral proteins may act as? |
Pores Channels Carriers (all 3 provide routes for water soluble substances across the hydrophobic bilayer) |
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How do cells regulate their intracellular environment and carry out specific cellular functions? |
1. expressing specific transport proteins 2. regulating transport proteins |
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Flux |
amount (mass) of solute which crosses a boundary (membrane) per unit of time units= moles/cm^2 x sec |
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Types of flux |
1. unidirectional influx - Joi 2. unidirectional efflux - Jio 3. Net flux (algebraic sum) |
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Jnet = 0 |
solute is either at a steady-state or at equilibrium |
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Rate of transport for passive uncoupled transport is determined by? |
1. Pathway (both the properties of individual proteins and the # present in the plasma membrane) 2. The size of the electrochemical gradient for the transported solute (which affects the direction of transport and size of the driving force) |
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Vm |
Voltage difference across the membrane |
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Nernst equation |
describes the conditions when an ion is at equilibrium across a membrane, only when the membrane potential is equal to the equilibrium potential Vm = Ex |
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Diffusion |
random movement of solute particles, results in net transport across a boundary, if there is an electrochemical gradient for that solute |
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Diffusion of a solute can occur through? |
1. water in both ICF and ECF 2. across the "phospholipid" portion of the bilayer 3. water filled passages through pores, channels, and portions of carriers |
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Rate of transport for non-electrolyte by solubility/diffusion mechanism is? |
Jx = Px ([X]o) - ([X]i) |
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P = Permeability coefficient, what does it account for? |
P accounts for the fact that w/ same conc. gradient, different solutes diffuse at different rates. |
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What is K? |
K is the oil/water partition coefficient |
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What is the most important property of movement across same concentration gradient? |
the ability of the solute to dissolve in the bilayer (=K) |
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Diffusion distance vs time required for diffusion? |
Distance away increases a factor of 100 when the distance away increases by a factor of 10. |
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What is the only effective method to move solutes over a short distance? |
Diffusion |
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What are two characteristics of transport via diffusion? |
1. Concentration gradients cannot be created or maintained 2. Solutes do not do not compete with each other (ie presence of solute B has no effect on the rate of diffusion of solute A, Diffusion of A is only proportional to concentration gradient of solute A) |
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How do electrolytes and polar non-electrolytes cross the bilayer membrane? |
Via pores, channels and carriers (NOT by the solubility/diffusion mechanism) |
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All solutes diffuse down their electrochemical gradient, but what is the driving force for non-electrolytes? what are the forces to consider for electrolytes? |
1. Non-electrolytes: concentration gradient only 2. Electrolytes: concentration gradient and membrane potential |
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Aquaporin |
forms a pore for water, present in membranes with high permeability to water |
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How are protons and ions excluded from aquaporin? |
Protons and ions are excluded by positive charges on one side of the pore and negative charges on the other side. |
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Ion Channels |
1. routes are formed by specific transmembrane proteins 2. electrolytes and some amino acids 3. open and close but do not bind solute or change conformation to transport solute |
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What are ion channels functionally composed of? |
A gate, a sensor for the gate, a pore, and a selectivity mechanism. |
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Voltage-gated channels |
have sensors that detect changes in the membrane potential (sensitive to membrane potential changes) |
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Ligand-gated channels |
have gates that are controlled by binding of hormones, neurotransmitters, and second messengers |
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Stretch-activated channels |
Opened/closed by mechanical pressure ie senses stretch in endothelial cells, cardiovascular system, pulmonary vascular function and possibly cell volume control |
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What is the most common channel? |
K+ leak channel |
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What are two special properties of channels? |
1. ability to open and close quickly 2. Ability to transport millions of ions per second |
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Examples where the critical role of a fast (milisecond) response of a channel may be required? |
Muscle contraction action potentials generator potentials calcium signaling in mechanisms of hormone action |
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Factors that affect ion selectivity |
relative size of ions degree of ion hydration size and characteristic of channels |
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How do cells regulate the movement of impermeable molecules via transport proteins? |
1. cells control kinds of proteins expressed 2. regulate where proteins are inserted into the PM (ie apical versus basolateral in epithelial cells) 3. Regulation of when proteins are expressed in cell cycle 4. how proteins are regulated |
