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26 Cards in this Set
- Front
- Back
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Concept of Passive Diffusion across an ideal semi-permeable membrane:
• how a substance moves • what drives its movement • the ultimate result • how equilibrium and net flux relate - when it is greatest/least • The dependent variables of net flux for neutral particles |
• Driven by random thermal motion, a substance freely moves through an ideal semi-permeable membrane and down its concentration gradient until it is uniform through out the compartments.
• Once uniformity/equilibrium is reached, the substance can still move between compartments but net flux is zero. Net flux is greatest when the concentration difference is greatest and progressively decreases as the substance equilibrates. • For neutral particles, Net Flux (Jx) is dependent on Px which is specific for a molecule, Surface area of the membrane and the concentration in & out of a cell. Jx = (Px)(A)[Xo-Xi] |
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How passive diffusion changes [solute] btwn compartents
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As a solute moves down its concentration gradient, the rate at which a compartment loses solutes while the other gains solute are at equal absolute values. The rates steadily slow down until equilibrium is reached
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Factors that can affect Net Flux across a membrane (6)
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• A concentration gradient: large disparity in [particle] ∝ greater flux btwn compartments
• An electrical gradient: for charged particles, flux will be greater if the side it is moving towards has an opposite charge • Temp: Higher temp ∝ Greater Jx • Membrane surface area: SA ∝ Jx • Molecular Mass: MM (1/∝) Jx • Membrane permeability: Px ∝ Jx |
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The conditions needed for calculating net flux, Jx (3)
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Particle is uncharged, the temperature is fixed and the membrane must be semi-permeable
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Ion Channels: • mechanism of action • how it influences Jx
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• It uses membrane proteins such as ion channels to allow specific permeablity towards an ion species, allowing it to move down an electrochemical gradient
• by increasing Px for a specific ion species, Jx also increases |
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Factors involved in the regulation of ion channel opening/closing (3)
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Ligand-gated: a specific molecule binds to a site on the ion channel, changing its conformation and leading to it opening or closing Voltage-gated: a change in the membrane potential causes crtain charges to move into the channel, leading to the channel's opening or closing Mechanosensitivity: deformation/stretching the membrane affects channel conformation and its opening/closing
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Channel specificty and factors (2) that determine it
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The selectivity some channels may have for the type of ion allowed to pass through. Two determinants are: - the diameter of the channel - the charge of proteins within the channel wall
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Membrane pores: • type of channel • dependent variable • what does not affect it • an example
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they are ungated channels, dependent on the concentration gradient and are not affected by opening/closing times. Ex. aquaporins
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Mediated Tranport:
• what it allows particles to do, comparitively • the kind of carrier molecules involved • what it requires the solute to do • what happens with the conformational change |
Mediated Tranport:
• allows for a faster flux of particles than their natural Px allows • integral membrane transporters • bind to a specific site on the carrier protein • the conformational change leads to the site now being exposed on the other side of the membrane |
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Factors determining the rate of transport (4)
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• Saturation of transporters - [Solute] and affinity of the binding site for the solute will determine whether the binding sites will be fully occupied
• Number of transporters - more ∝ flux • The time it takes for the protein carrier to undergo the conformational change • the electrochemical gradient of the solute across the membrane |
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Two types of mediated transport
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Facilitated diffusion and active transport
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Mechanism of facilitated diffusion
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the solute that is to be carried across the membrane, binds to a site on the protein, leading to a conformational change on the carrier andit passing through to the other side
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A graph of net flux vs [gradient] for faciliated diffusion: • reason why it has a shape • when it becomes [independent]
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As conc. increases, Jx increases non-linearly, due to the time it takes the carrier to tranport the substance across the membrane. When all transport proteins are saturated, Jx is at a maximum and any increase to conc. will not affect Jx.
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Transport maximum
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When all transport proteins are saturated, Jx is at a maximum and any increase to conc. will not affect Jx.
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Active Transport: • the direction it allows substrates to move • what it must utilize • the two types
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Allows particles to move against their electrochemical gradient with the use of an energy source in the form of ATP or a [gradient]. There are 10 and 20 forms of active transport.
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Primary Active Transport:
• the protein it uses • the driving force of the process • normal mech |
Primary Active Tranport:
• Typically uses an ATPase • which uses the hydrolysis of ATP as the driving force • Usually, the solute to be moved across the membrane & against its electrochemical gradient, binds to the ATPase, leads to the hydrolysis of ATP and the conformational change of the enzyme. The change alows the solute to be deposited on the opposite sid of the membrane. |
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Secondary Active Transport: • the protein it uses • the driving force of the process • normal mech
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Secondary Active Tranport:
• Uses a transport protein • which uses an [ion] as the driving force to move one solute against its [gradient] • The transport protein has one binding site for the ion that is to be moved down its [gradient] and another for the other particle to be moved against its [gradient] |
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Primary vs Secondary Active Transport (2)
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• The driving force: ATP vs a [gradient]
• Primary - usually both particles are being moved against [gradient or electrochemical gradient while secondary - one particle travels with its [gradient] or electrochemical gradient and the other against it |
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Two types of 20 active transport, their mechanisms and one example of each
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• Both utilize the movement of one solute going down its gradient to pump other solute against its gradient but for Co-transporters, the solutes are going int the same direction while in Active exchangers, the solutes are goin in opposite directions. Ex co-transporter: Na+/Glucose Ex. of Active exchanger: Na+/Ca2+
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Endocytosis and Exocytosis
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Endocytosis: A part of the plasma membrane engulfs some of the extracelluar fluid, piches off and releases the contents inside of the cell.
Exocytosis: within the cell, a membrane bound vesicle with intracellular contents, moves to the plasma membrane, fuses with it and releases its contents into the ECF. |
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Epithelial Transport:
• Occurs across these cell types • number of membranes the solute must cross • And the position of each membrane • The property of membranes allow for the directional transport of substances across the epithelia and how its generated |
Epithelial Transport:
• Occurs across cells that line hollow organs or tubes • The solute must cross two membranes: - An Apical membrane that is in contact with the luminal/ECF - A Basolateral membrane which is in conact with the interstium and blood • Membrane Polarity allows for directional transport across epithelia and is generated by transporters and pumps |
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Dalton's Law
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The total prssure of a mixture of gasses is equal to the sum of the partial pressures of each individual gasr
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How gases generally move
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From an area of high pPressure to one that is low.
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Determinants of whether a gas will dissolve in a liquid (3)
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> The pPressure of the gas > The gas's solubility in the liquid > The temperature
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Only this state of gas contributes to pPressure
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free/unbound state
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Henry's Law and explain variables
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Dissolved Gas plasma = Ks x Pplasma where Ks = the solubility constant of that particular gas in plasma
Pplasma = the pPressure of the gas in plasma |
