Membrane Transport Mechanisms Syed Flashcards
The sodium potassium pump is an example of which of the following kinds of transport? A. Diffusion B. Primary active transport C. Secondary active transport D. Facilitated diffusion
Primary active transport - ATP is directly involved in providing energy for the transport
The sodium-glucose pump is an example of which of the following kinds of transport? A. Diffusion B. Primary active transport C. Secondary active transport D. Facilitated diffusion
Secondary active transport
The sodium-calcium pump is an example of which of the following kinds of transport? A. Diffusion B. Primary active transport C. Secondary active transport D. Facilitated diffusion
Secondary active transport
Glucose transporters (GLUT transporters) employ kind of transport?
Facilitated Diffusion
What’s the difference between Diffusion and Osmosis?
Diffusion is the movement of particles from an area of high concentration to low concentration
While Osmosis is the movement of a solvent across a semi-permeable membrane from high to low concentration
**Semi-permeable membrane is required for osmosis, but not for diffusion
What does it mean when equilibrium is met across a membrane?
It does not mean that water or something isn’t moving anymore. It moves left and right, but the net movement is equal
What is osmotic pressure?
The pressure that has to be applied to a solvent to stop it from passing into a solution by osmosis. It depends on the concentration of the osmotically active particles aka solution (Van’t Hoff’s Law)
What is the osmotic pressure equation?
Pi = g * C * RT
Osmotic Pressure = (Number of particles in solution ism/mol) * Concentration mol/L * gas constant * Absolute temperature
How do you calculate Effective osmotic pressure?
Osmotic pressure * Reflection coefficient (Rho)
What is the reflection coefficient?
It is the ease with which a solute permeates a membrane
1 = impermeable; 0 = completely permeable.
What does a reflection coefficient closer to 1 represent?
It means that that membrane is a major contributor to osmotic pressure and letting things through. It is responsible for controlling the environment
What are the pressure differences between A and B?
ADD PICTURE
Column A has a lot of pressure because it is higher and with gravity, it is pushing on the membrane
What are the two types of non-gated channels?
- Aquaporins - channels that are permeable to water
- Ion channels
What are the two type of gated channels and what do they do?
- Ligand Gated - They open and close and respond to a kind of signal channel (such as a hormone)
- Voltage Gated - They open and close based on a voltage channel
What is the difference between Primary and Secondary Active Transport?
Primary active transport - Energy is derived from breakdown of ATP
Secondary active transport - Energy is derived from energy that has been stored in the form of ionic concentration differences of secondary molecular or ionic substances. Secondary active transport also requires multiporters
What are multiporters and what are the two kinds?
Symporters (cotransporters) and antiporters (countertransporters or exchangers)
They transport two or more substances across the membrane in either direction.
What are some molecules that can diffuse across the biphospholipid layer?
Oxygen, CO2, Nitrogen, alcohols diffuse readily because they are soluble
What factors affect the RATE of diffusion?
- Proportional to concentration difference across membrane (hyper vs hypo)
- Membrane electric potential (Nernst potential) - if one side is positive, etc
- Pressure difference - Piston example
What factors increase permeability for diffusion?
- Increase in oil/water partition coefficient
- Decrease in size of solute
- Decrease in membrane thickness
What is special about simple diffusion?
Simple diffusion (including osmosis) is the only form of transport that is not carrier mediated
Equation for measuring diffusion
J = - P*A(C1 - C2) J = flow(flux) in mmol/sec P = permeability in cm/sec A = area in cm2 C1 = [ ]1 in mmol/L C2 = [ ]2 in mmol/L
Describe facilitated diffusion in relation to carrier proteins
- Have binding sites on both sides of membrane
- Very stereospecific to what they transport
- It changes states to get it in. But, the rate at which molecules can be transported by this mechanism can never be greater than the rate at which the carrier protein molecule can under change back and forth between its two states. Remember that it’s still diffusion
What is an example of facilitated diffusion?
Glucose. Its transport can be activated by insulin. All cells have members of the GLUT (glucose transporter) family of proteins
How does the rate of facilitated diffusion change compared to simple diffusion?
The rate of facilitated diffusion can never be higher than Vmax, while the rate of simple diffusion increases proportionally as concentration increases. (See graph)
How does the selective filter of the potassium channel work to stop sodium from entering the channel?
The problem with this channel is that it is always on. But sodium ions are smaller than K ions. So why doesn’t Na always go through? Sometimes it does, but what happens is that it has a selectivity filter. One a hydrated K comes through the filter in front of the channel, it is big enough to bind with the edges in the selective filter, to become dehydrated. But the hydrated Na is too small and can’t bind. Hydrated BUT, the hydrated Na ions are actually bigger than the dehydrated K ions. So that is where the selectivity comes from
What is the patch-clamp method?
They take a patch from the cell and test for it inside a free solution. It can measure current flow to learn about transport characteristics of the channel (pic)
How does secondary transport get its energy from sodium?
The movement of Na out of the cell releases energy. This can then be used to either pump something else in or out.
If sodium moves down its electrochemical gradient, why is this referred to as secondary active transport?
It requires ATP to set up the gradient in the first place.
We always have to keep moving the Na out of the cell so we keep the gradient so that we can move it back down the cell.
Sodium/calcium antiporters move three sodium ions per calcium ion. Why does it take three sodium ions to move one calcium ion?
Calcium is a larger ion, so it has a larger electrochemical gradient. So it needs more energy to move the calcium ion.
Why do we pump out 3Na for only 2K?
It helps maintain the negative environment inside the cell, which is extremely important for many biological processes
Explain the secondary active transport for Na/Glucose co-transport.
A sodium gradient is created by primary active transport, with sodium more concentrated outside the cell. It then moves to secondary active to move the glucose in. As Na diffuses in, it uses that energy to move the glucose in.
Explain the active transport of Na across a layer of cells
Once there is a lot of Na in the cell (through diffusion), the gradient is no longer there. So then we actively transport it out of the cell and water will follow too through osmosis because it follows concentration gradients.
