Lecture 2 Flashcards
(27 cards)
Acetyl choline channel
Allows uncharged molecules or positive ions smaller than its diameter to pass through. Important for transmission of nerve signals from nerve cell to nerve cell to cause muscle contraction
Voltage-Gated Channels
-Go from open state to closed state very fast or slow depending on action potential(volts)
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
Na/K pump for Cell Volume
The pump helps protect the cell from swelling. The device pumps 3Na+ ions to the outside of the cell for every 2 K+ pumped inside. The membrane is much less permeable to Na ions than it is to K ions, so once the Na ions are on the outside, they have a strong tendency to stay there. This process yields a net loss of ions out of the cell, which initiates osmosis of water out of the cell as well. THe moving of the ions unequally causes the water to move outside with it
The Sodium potassium pump is an example of which of the following kinds of transport?
Primary active transport, because ATP is directly involved in providing energy for the transport
Glucose transporters(GLUT transporters) employ which of hte following kinds of transport
Facilitated diffusion
The sodium-glucose pump is an example of which of the following kinds of transport?
Secondary active transport
What about the sodium-calcium pump?
Secondary active transport
Diffusion
Movement of particles from an area of high concentration to low concentration
-Net diffusion occurs across a barrier(more molecuels moving one way than the other) if there is a driving force(a concentration gradient or ,for charged molecules , a potential gradient) and if the barrier is permeable
Osmosis
Movement of a solvent across a semi permeable membrane from high concentration to low concentration
- semi-permeable membrane is required for osmosis ,but not diffusion
- -With regard to living organisms and the cell , the solvent is water , so osmosis is usually defined as the movement of water from a region of high concentration to a region of low concentration across a semipermeable membrane–essentially a cell membrane
Osmotic Pressure
- When water moves across a cell membrane(semipermeable membrane) because of the concentration differences water will accumulate on one side of the membrane. This will usually create a higher pressure on one side of the membrane than on the other side. This increase in pressure is osmotic pressure.
- -The amount of pressure required to stop osmosis is called osmotic pressure of the solution
- -Osmotic pressure depends on the concentration of osmotically active particles(van’t Hoff’s law)
Osmotic Pressure Formula
the factor that determines the osmotic pressure of the solution is the concentration of the solution in terms of number of particles
–pi=gCRT
g=number of particles in solution
C=concentration
Effective osmotic pressure
osmotic pressure * reflection coefficient(sigma)
Sigma refers to ease with which a solute permeates a membrane(1=impermable; 0=completely permeable)
This is calculated by taking the osmotic pressure(pi) and the reflection coefficient. If the RC is clsoer to 1 ,then that means that membrane is a major contributor to osmotic pressure and letting things through which mean it’s responsible for controlling the environment. But it it’s close to O , then that means it lets almost anything through and doesn’t do much in terms of selection
Mechanism for crossing Cell Membranes
Energy independent(except for kinetic energy)
-Diffusion
-Osmosis
-Facilitated diffusion
Requires channels:
–non-gated:means they are always open
—-aquaporins
—-ion channels
–gated:they open and close
—-Ligand gated:they respond to some kind of a signal channel . can be a hormone
—–Voltage gate:these will open or close based on a voltage change
Active transport
Primary:energy is derived from breakdown of ATP and requires ATPases
-ATPases-enzymes that split the phosphate off the ATP to transfer energy
Secondary:energy is derived from energy that has been stored in the form of ionic concentration differences of secondary molecular or ionic substances
–requires multiporters(transport two or more substances across the membrane in either direction) :
—symporters(cotransporters)
—Antiporters(countertransporters or exchangers)
Diffusion
- Movement of particles from an area of high concentration to an area of low concentration to an area of low concentration
- depends on kinetic energy of particles rather than an external energy source(metabolic energy)
- diffusion across biphospholipid layer:
- –oxygen,CO2, N, OH diffsue easily because they are soluble
(diffusion)Factors affecting rate of diffusion
- proportional to concentration
- membrane electric potential (Nernst potential)
- Pressure differenece
(diffusion)Factors that increase permeability
-Oil/water partition coefficient increase
-size of solute decrease
-Membrane thickness decrease
simple diffusion (including osmosis) is the only form of transport that is not carrier mediated
Diffusion equation
J= -PA(C1-C2)
-indicates that direction of flow is from high to low concentration. Ignore if Cl is higher concentartion and C2 is lower concentration
-P=permeability in cm/sec
-A=area in cm^2
J=flow(flux) in mmol/sec
Osmosis
Diffusion of a solvent(water)across a semipermeable membrane
Facilitated diffusion
- requires uniporter carrier proteins
- -occurs down an electrochemical gradient
- -a uniporter has binding sites that are alternately available on eitehr side of the membrane
- -carrier medaited transport establishes stereospecificty
- -structurally similar solutes may compete for transport sites on carrier molecules
- -All cells have members of the GLUT family of proteins
- -chagnes states to get it in,but the rate at which molecuels can be transported by this mechanism can neer be greater than the rate at which the carrier protein molecule can udnergo change back and forth between its two states
What is the highest rate facilitated diffusion can reach?
Facilitated diffusion can never be higher than Vmax, while the rate of simple diffusion increases proportionally as concentration increases
What is the function of the selectivity filter and how does it work?
- -Problem with this channel is that it is always on
- -Sodium ions are smaller than K ions , so why doesn’t Na always go through?
- -Well sometimes it does,but what happens is that it has a selectivity filter. Once, a hydrate K comes through , it is big enough to bind with the hydrogen to become dehydrated.
- -But the hydrated Na is too small and can’t bind. Hydrated sodium ions are actually bigger than the dehydrated K ions. so that is where they selectivity comes from
Secondary active transport
- Multiporters include symporters and antiporters
- In secondary active transport, at least one of the solutes moves down its electrochemical gradient while one orm ore of the other solutes moves up its electrochemical gradient
- sodium is often one of the solutes invovled in secondary active transport
- -Na is more concentrated outside the cell
- Movement of soiudm into cell(down its electrochemical gradient) generates the energy needed to transport another substance against its electrochemical gradient
