Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
79 Cards in this Set
- Front
- Back
|
Passive Transport/ Simple Diffusion is
[Lecture 3 Slides] |
Substances diffusing down their concentration gradient. Mechanisms of passive diffusion can only move material in the direction of equilibrium. NO ENERGY IS REQUIRED
|
|
|
Simple Diffusion is
[Lecture 3 Slides] |
This is the movement of a solute from an area of high concentration to an area of low concentration. This is simply because in the area with high concentration, there are more movements that successfully take the solute through the semi-permeable membrane to the other side. Diffusion stops when concentrations are equal and the rate of successful collisions with the membrane are equal
|
|
|
What is Fick's Diffusion Equation?
[Lecture 3 Slides] |
J = D(C1-C2)/X
J = rate of substance flow (per unit area, per unit time) D = diffusion coefficient C1-C2 = difference in concentration X = distance separating them D is empirically determined for each solute/solvent combo |
|
|
How is D, the diffusion coefficient in Fick's Diffusion Equation calculated?
[Lecture 3 Slides] |
D = (RT)/(6 pi n s N)
where R = gas constant T = temp N = Avogadro's number n (which isn't the regular n, right side has longer leg) = solvent viscosity s = solute radius |
|
|
In sum for Fick, what increases diffusion, what decreases diffusion?
[Lecture 3 Slides] |
Increases: decreased viscosity, decreased radius, increased temperature, decreased distance between, increased difference in concentration.
For decreasing the rate of diffusion, use the opposite of the above. |
|
|
What is the simplified version of Ficks Equation?
[Lecture 3 Slides] |
J = P * (C2-C1)
P = membrane permeability C2-C1 is the concentration difference |
|
|
Diffusion of ions and other charged molecules are influenced by the following 2 factors:
[Lecture 3 Slides] |
1. The concentration (chemical) gradient
2. The electrical gradient: the charge of the atoms and the forces of electrical attraction & repulsion |
|
|
What holds priority, the chemical gradient or the electrical gradient? Explain
[Lecture 3 Slides] |
The chemical one. An ion will move down its concentration gradient until it is opposed by the electrical gradient
|
|
|
Electrical gradients are (dependent/independent) on/of solute identity. Pick the right answer
[Lecture 3 Slides] |
independent. See Slide 10 of Lec 3 slides for a good explanation of chem vs electrical gradients
|
|
|
The cytoplasm is full of proteins with a _________ charge
[Lecture 3 Slides] |
negative. They can also not diffuse across the membrane thus contributing to the negative potential difference that exists across the membrane
|
|
|
Facilitated Diffusion, define it 4 Major points
[Lecture 3 Slides] |
transport/carrier proteins speed up the passive movement of molecules across the plasma membrane.
1. This occurs IN THE DIRECTION OF THE GRADIENT. 2. Rate is faster than in the absence of the transporter protein 3. Requires that the solute bind reversibly to the transporter 4. Does NOT require energy and is therefore passive. |
|
|
Active Transport, define it. 3 Major Points
[Lecture 3 Slides] |
Is necessary to allow cells to maintain concentration gradients that differ from their surroundings:
1. Moves substances again electrical and/or chem gradient 2. Requires energy, usually ATP 3. Performed by specific proteins embedded in the membrane. The sodium-potassium pump is the best example. EXCHANGES 3 NA+ FOR 2K+ |
|
|
Na+-K+-ATPase, how does it work?
[Lecture 3 Slides] |
Hydrolyzing ATP provides the energy to trigger a conformational change. The conformational change influences the ability of the Na-K-ATPase to bind the ions. [look in book and discussion notes for more detail]
|
|
|
Secondary Active Transport, what is it?
[Lecture 3 Slides] |
The transport of glucose across intestinal cells is the given example.
1. Na-K-ATPase on the basal surface transports Na+ out of the cell UP ITS ELECTROCHEMICAL GRADIENT (aka against). 2. At the apical surface, Na+ flows down its gradient into the cell 3. As Na+ enters with an assist from a cotransporter, it 'forces' glucose to enter AGAINST its gradient. |
|
|
Explain the secondary active transport of glucose.
|
Na-K-ATPase takes Na out of the cell via its basal surface against the gradient, as Na flows back in with help from a cotransporter, it brings in glucose with it, against glucose's gradient.
|
|
|
What is Osmosis?
[Lecture 3 Slides] |
the diffusion of water across a semi-permeable membrane. Region of lower solute concentration into higher. Great the difference in conc. the faster the rate
|
|
|
Colligative properties include (list a few examples), and are independent of (blank 1), and depend solely on the (blank 2) of dissolved molecules.
[Lecture 3 Slides] |
examples: boiling point elevation, freezing point depression
blank 1 = independent blank 2 = number. Colligative properties depend on the mols of solute over kg of solvent. |
|
|
How does water move across cell membranes? Why is this surprising? What might allow this to happen? What speed is this at?
[Lecture 3 Slides] |
It dissolves into the phospholipid bilayer.
-This is surprising because water is polar. -It's small size helps it dissolve in. -It's slow though, about ~1/10,000 the rate of diffusion of water in free solution |
|
|
What are aquaporins?
[Lecture 3 Slides] |
Protein channels specialized to allow water to move across membranes via osmosis. This happens fast
|
|
|
What is a piston osmometer and how does it work?
[Lecture 3 Slides] |
It's a tool to measure the osmotic pressure of a solution; the difference in hydrostatic pressure that must be applied between 2 solutions to prevent the net osmotic movement of water. See slide 24 for images
|
|
|
Water Pressure (= or =/=) hydrostatic pressure
[Lecture 3 Slides] |
DOES NOT =.
this is a terrible and convoluted idea. Blame it on booker and the physicists. |
|
|
Does active transport always carry molecules opposing the gradient?
|
NO. (pp. 101)
|
|
|
What is the concentration gradient expressed mathematically in symbols?
|
(C1-C2)/X (102)
|
|
|
What is the Boundary Layer?
|
The Boundary layer is an area of elevated solute concentration right next to a cell or animal's surface. As solute diffuses outward (for example), from the cell, the particles are more concentrated near the cell and less concentrated further away. This overall decreases the rate of diffusion because the concentrations on the two sides of the barrier are now more similar than the average concentration on both sides. 102
|
|
|
Define bulk solution
|
bulk solution is the solution that is away from contact with a membrane - also, the concentrations of positive and negative charges are always equal. Net charge zero. (103)
|
|
|
Where is the electrical gradient relevant?
|
The electrical gradient only truly exists in the few nanometers within the membrane. The lipid bilayers can develop a concentration of charge based on whether anions or cations have a sum majority on that side of the barrier. (103)
|
|
|
Name a few types of solutes
|
lipids, molecular oxygen (O2), thyroid hormones, steroid hormones, inorganic ions (104)
|
|
|
What are the properties of lipid solutes? What are they?
|
Lipid solutes include steroid hormones and fatty acids, which are hydrophobic. Both of these dissolve in the lipid interior of a call membrane and then make their way down the gradient based on the principles of simple diffusion (104)
|
|
|
There are 3 types of molecules "generally believed to make its way through cell membranes primarily or exclusively by simple diffusion through the lipid layers without the need of channels or proteins".
|
molecular oxygen (O2) [small & nonpolar]
thyroid hormones [used in signaling] nitric oxide [also for signals] (104) |
|
|
At what rate do inorganic ions diffuse across membranes? Why?
|
They are hydrophilic and therefore do not dissolve in membrane lipids. Rates of diffusion are exceedingly low. They require ion channels to move at rapid rates (104)
|
|
|
What is the defining characteristic of ion channels?
|
They allow the PASSIVE transport of ionroganic ions by diffusion through a membrane. Ion channels do not bind to the ions that pass through them. They are composed of one or more protein molecules that cross the entire membrane. They are selective and each will only allow a few types of ions to pass
|
|
|
What is a gated channel? What are the 4 types of gated ion channels? (105)
|
A gated channel can open and close because of the proteins they are composed of go through conformational changes. 1. voltage-gated, 2.stretch-gated (tension gated) 3. phosphorylation-gated, 4. Ligand-gated
|
|
|
Explain voltage-gated channels, briefly
|
open and close in response to voltage differences across a membrane. Important in the generation of nerve impulses
|
|
|
Explain stretch-gated channels, briefly
|
open or close in responses to stretching or pulling forces that alter the physical tension on a membrane
|
|
|
Explain phosphorylation-gated channels, briefly
|
open or close according to whether the channel proteins are phosphorylated (phosphate group attached)
|
|
|
Explain ligand-gated channels, briefly
|
closed in the absence of a signal but open when their receptor sites bind to the specific ligands allowing the passage selected ions.
|
|
|
What is the typical charge for an animal cell?
|
Positive outside, negatively charged on the inside (105)
|
|
|
What are the 3 ions we care about?
|
K+, Na+, Cl-
|
|
|
What's the standard situation look like for Cl- in terms of concentration?
|
Cl- is usually more concentrated outside a cell than inside but the negative charge of the cell repels Cl- from diffusing across its chemical gradient. The two gradients cancel and Cl- is usually at electrochemical equilibrium
|
|
|
What's the standard situation look like for Na+ in terms of concentration?
|
Both electro and chemical gradients are pushing Na+ into the cell. Na+ uses resting channels to get in (b/c it can't dissolve across membrane)
|
|
|
What's the standard situation look like for K+ in terms of concentration?
|
it's not at electrochemical equilibrium but it's not as far from eq as Na+ is. The [K+] is usually high in cells, overwhelming the electrical gradient and thus K+ diffuses out via resting channels.
|
|
|
What are resting channels? (106)
|
channels that are usually open (all or most of the time) and they allow Na+ to leak across the cell membrane into the cell.
|
|
|
Why can't polar organic solutes diffuse across the membrane?
|
They're hydrophilic, there are no channels for them. They rely on transporters
|
|
|
What's another name for active transport?
|
uphill transport (108)
|
|
|
What's the difference between simple diffusion and facilitated diffusion?
|
Neither uses energy, both go in the direction of the gradient BUT facilitated goes much faster and requires solutes to bind reversibly with transporter proteins
|
|
|
What is carrier-mediated transport and what falls under this category?
|
Transport that requires proteins (transporter or carrier). This includes facilitated diffusion and active transport.
|
|
|
What kind of kinetics does carrier-mediated transport exhibit?
|
Saturation kinetics (see pg 42)
|
|
|
Can active transport create voltage differences? If so, how?
|
Whereas active transport can transport ions, but separating cations and anions on opposite sides of a membrane, a net voltage is established.
|
|
|
What do the terms electroneutral (nonelectrogenic) and electrogenic mean?
|
The first refers to a mechanism that does not generate an imbalance of electrical charge. The second does create an imbalance.
|
|
|
What does the Na+-K+ pump move?
|
It hydrolyzes ATP enabling it to move 3 Na+ ions out of a cell and 2 K+ ions into a cell. Both of these are against the gradient, this creates a charge difference as well.
|
|
|
Where is the Na+-K+ pump found?
|
In the basolateral membrane of all epithelial cells
|
|
|
This is the best known transporter protein: Na+-K+-ATPase. Explain the name and function
|
It's called an ATPase because it is an enzyme that catalyzes the hydrolysis of ATP as well as a transporter. It is the transporter protein that enables the Na+-K+ pump. It goes through multiple conformational changes and bindings in one pumping cycle
|
|
|
What are P-type ATPases?
|
P-type ATPases are phosphoryated and dephosphorylated during each pumping cycle
|
|
|
What is step 1 of the Na+-K+-ATPase pump?
|
1. On the cytoplasm side, the 3 Na+ bind to the cation binding sites as 2K+ are expelled into the intracellular fluid. ATP is bound at the ATPase catalytic site and is hydrolyzed causing a conformational change
|
|
|
What is step 2 of the Na+-K+-ATPase pump?
|
2. The 3 Na+ are now occluded (touching neither body of liquid) within the protein. The ATP has left as ADP. The energized protein not has another conformation change
|
|
|
What is step 3 of the Na+-K+-ATPase pump?
|
3. The channel to the outside of the cell opens, the cation-binding sites change affinity so that 3Na+ is expelled and 2K+ are bound. Also, an ATP is bound at the ATP regulatory site (different from the CATALYTIC site earlier). It exerts modulatory effects here but is not hydrolyzed. The protein dephosphorylates which causes another conformational change
|
|
|
What is step 4 of the Na+-K+-ATPase pump?
|
4. The 2K+ are now occluded. The ATP shifts from the ATP regulatory site to the ATP catalytic site and the process begins again from step 1.
|
|
|
Where is the Na+-K+-ATPase pump?
|
It's on the basolateral membrane. Therefore, it carries Na+ into the bloodstream (in theory). The apical side of the intestinal epithelial cell faces the intestinal lumen. There, the Na+ concentration still high, maintaining a gradient that goes from the lumen, through the apical membrane, into the cell.
|
|
|
What is Primary Active Transport?
|
active transport that draws energy immediately from the hydrolysis of ATP. That is, the transporter protein in primary active transport is an ATPase
|
|
|
What is secondary active transport?
|
Secondary active transport draws energy from an electrochemical gradient of a solute. ATP is required for secondary active transport but it's no the energy tapped by the transporter. Instead, ATP is used to create a gradient which is then used by the transporter protein to drive transport.
|
|
|
How is glucose transported into the cell?
|
Through an obligatorily linked transport of Na+ and glucose. The transporter that takes Na+ from the intestinal lumen through the apical membrane into the cell must carrier a molecule of glucose in the same direction "because of its particular chemistry".
|
|
|
How does Na+-K+-ATPase pump allow for the pumping of glucose into the cell?
|
The sodium potassium pump takes sodium out of the cell via the basolateral side, maintaining a gradient on the apical side necessary for the transporter protein that brings in sodium with glucose.
|
|
|
Why does the glucose movement count as active transport?
|
Because a gradient is a form of potential energy and when the glucose moves against its gradient, it can only do so by using the potential energy of the Na+ gradient. As the concentrations of Na+ inside and outside of the cell equalize, the potential energy decreases.
|
|
|
Why is the transport of glucose secondary active transport?
|
1. goes against the gradient (therefore not passive)
2. is carrier mediated (therefore active trans or at least facilitated) 3. uses energy but not ATP (this is really why it's secondary) |
|
|
Organic solutes are usually ______________ transported by animal cells using ________________.
|
1. actively transported
2. secondary active transport |
|
|
The act of moving two solutes in linked fashion in one direction is called ______________ and done by a _________________.
|
1. cotransport
2. cotransporter |
|
|
The act of moving two solutes in linked fashion in opposite directions is called ______________ and done by a _________________.
|
1. countertransport
2. countertransporter |
|
|
What are the 4 colligative properties?
|
1. freezing point depression
2. Boiling point elevation 3. osmotic pressure 4. water vapor pressure of a solution (the last 3 are the important ones in physiology) |
|
|
define osmotic pressure
|
the property that determines whether a solution will gain or lose water by osmosis when it undergoes exchanges with another solution
|
|
|
define freezing point depression
|
the difference between the actual freezing point of a solution and the freezing point of pure water
|
|
|
define water vapor pressure depression
|
the difference between the actual water vapor pressure of a solution and the water vapor pressure of pure water
|
|
|
Why are all colligative properties linked and proportional to each other?
|
Because they all depend on the concentration of dissolved entities in solution, once you know the proportion for one value, multiply it by a different constant for the other values.
|
|
|
Why do suspended materials like pebbles in water have no effect on colligative properties?
|
They aren't actually dissolved. Other examples include clay in water, blood cells in blood plasma
|
|
|
What happens with electrolytes in solution in the context of colligative properties?
|
Strong electrolytes like NaCl will disassociate, doubling the concentration. Because they aren't 100% separate entities in solution, it doesn't work out perfectly as in 1NaCl -> 1 na+ and 1cl- but we pretend it does.
|
|
|
What is the name of the system for osmotic pressure? What are the units?
|
Osmolarity system, 1-osmolar (Osm) is the unit which is equal to 1 mol per liter.
|
|
|
What instruments are used to measure osmotic pressure?
|
Freezing point osmometers and vapor pressure osmometers. They use the ratio from one colligative property to calculate another.
|
|
|
What is the mathematical expression for the rate of osmotic water transport per unit of cross-sectional area?
|
K (pi1-pi2)/X
where pi1 and pi2 are osmotic pressures, X is the distance separating them K is the proportionality coefficient that depends on the temperature and permeability of the membrane. |
|
|
What is the osmotic-pressure gradient, express mathematically?
|
(pi1-pi2)/X
|
|
|
What do the words isomotic, hyposmotic, and hyperosmotic mean?
|
Iso means the same osmotic pressure, hypo is lower, hyper is greater.
|
