Membranes Flashcards
Why wouldn’t you want an IV of distilled water?
Distilled water has a higher concentration of water than the cells do so the water will flow into the cells and cause them to burst.
What does amphipathic mean?
Mostly a term for proteins, means having both hydrophobic and hydrophilic ends.
Are proteins in the bilayer polar or non-polar?
All membrane proteins in the bilayer are polar.
What is the difference between integral membrane proteins and peripheral membrane proteins?
Peripheral membrane proteins are not found in the bilayer. They are instead found on the surface usually bounded to membranes through indirect interactions with integral proteins or direct interactions with polar heads of the phospholipid. Integral membrane proteins either go all the way through the membrane, poking out on each side, or the just emerge on one side.
What is freeze fracturing and why does it only break the two leaflets of the bilayer, not the proteins aswell?
Freeze fracturing is a process of freezing a specimen and splitting it along a weak portions of the tissue such as the membrane or the organelles. The two layers of the membrane are held together very weakly by only van der waals forces therefore allowing them to be separated easily. When separated the integral proteins remain embedded in the membrane layer and our now much more visible.
What are planar lipid bilayers?
A planar lipid bilayer is a synthetic bilayer made in vitro opposed to in an actual organism.
What goes through a lipid bilayer and what doesn’t?
Gases, water molecules, glycerol, sucrose and glucose will all go through. ions and larger, more charged molecules will not go through either. Essentially the bigger and more charged a molecule gets the less likely it is to go through the bilayer.
What is the “random walk”?
The reason that molecules diffuse from more concentrated areas to less concentrated areas (concentration gradient). The random walk is the notion that molecules are constantly moving around and bumping into each other.
What does a steep concentration gradient mean?
It means the diffusion is highly favourable, there is a very negative delta G.
What is osmosis?
Osmosis is the diffusion of water from a less concentrated area to a more concentrated area.
What is the difference between a hypertonic solution, an isotonic solution and a hypotonic solution?
A hypertonic solution means that there is more water inside the cell than out so water will flow out of the cell, ex: salt water. An isotonic solution means there is the same concentration of water outside of the cell than in. A hypotonic solution means there is more water out of the cell than in so water flows into the cells. Ex: tap water.
Why are we ok if we drink a 200g glucose solution, like coke, but not if we drink a 200g solution of sodium chloride?
Glucose is very heavy so a 200g gram solution does not cause enough water to flow out of our cells to harm us. The concentration of water in the glucose solution is not as low as the concentration of water in the sodium chloride solution.
What is passive transport?
Passive transport is facilitated diffusion. There are charged ions that want to enter the cell but can’t so the cell has invented channels that can facilitate the transport of the molecules into the cell. There is an electrochemical gradient meaning a difference of charge across the membrane. A carrier protein is an integral protein that directly binds to the molecule and allows them to pass through. Ex: glucose binding.
What does it mean to say that a carrier protein can be saturated?
When all the binding sites on a carrier protein are occupied the rate of diffusion is said to be maximized and
What is active transport?
Active transport is transport against the concentration gradient, it requires energy.
How do you counteract the large delta g associated with active transport?
You have to couple the reaction with a reaction that has a very negative delta g such as atp hydrolysis.
Explain the what the sodium potassium pump does and why.
The sodium potassium pump is a form of active transport that works against both the electrochemical gradient and the concentration gradient. It breaks apart an atp molecule and uses that energy to release three sodium ions to the outside and bring two potassium ions inside. This causes a very steep electrochemical gradient and concentration gradient. This is commonly found in nervous cells and when something triggers it the sodium and potassium diffuse and help us feel, and touch etc.
What is vesicular transport?
A form of active transport where the work is done vesicles. Also called cytosis.
How does vesicular transport work and what is the difference between endocytosis and exocytosis?
Information is the form of neurotransmitters get packaged into vesicles, they travel to the membrane, fuses to the membrane and releases the neurotransmitters out of the cell and this is how we remember stuff. This process is exocytosis. The reverse is endocytosis (when information gets in).
What are secondary transport processes?
Secondary transport processes use gradients set up by sodium potassium pumps/active transport and helps other transport processes.
How does the sodium potassium pump help glucose get into the cell?
Sodium ions wanting to get into the cell that were pumped out during active transport can bind to glucose wanting to get in and lower the energy needed by the cell to bring the glucose in.
What are diffusion rates determined by?
Distance, temperature, size of molecule and steepness of concentration rate.
What is the difference between carrier proteins and channel proteins?
Both proteins are integral membrane proteins that transverse the entire membrane. Carrier proteins can be used in both active and passive transport however solute flow through channel proteins is always passive. A carrier protein also binds to the transported substance whereas a channel protein just opens and closes to let solute pass.
