L1 - Membrane Transport (Chapter 4) Flashcards
Who proposed the original model of the cell membrane?
Singer and Nickelson
What macromolecules make up the plasma membrane?
- Lipids (phospholipids) make up about half the mass
- Carbs (polysaccharides)
- Proteins make up about half the mass and are embedded in lipids
- Nucleic acids
What do proteins do in the plasma membrane? What are integral membrane proteins? Peripheral membrane proteins?
- make up ion channels, some are involved in adhesion, defense, signaling, etc
- integral - goes through the entire membrane/embedded in the membrane
- peripheral - only one one side of the membrane
What is the fluid mosaic model? What does that mean?
- model that explains the structure of the cell membrane
- considered fluid bc it moves and changes constantly, considered mosaic bc it has many different parts
Know the diff concentrations of the different ions in the table
- K is usually moving out of the cell
- Na is usually moving into the cell
- Ca is usually moving into the cell
- Cl is usually moving into the cell
How do you convert moles to equivalents?
Equivalents = moles X valence of ion
What causes diffusion?
driven by a chemical gradient, moves from areas of high concentration to low concentration
Brownian Motion
Particles are moving based on having thermal energy, molecular motion occurs at any temp above 0 degrees Kelvin
What is meant by describing diffusion across a membrane as dynamic?
Diffusion across membrane is said to be dynamic because the molecules keep on moving constantly.
What is the difference between diffusion and net diffusion?
- diffusion is a vector quantity that has direction and magnitude, typically occurs in one direction
- net diffusion is the Total amount of diffusion occurring/total movement of a molecule
What context is normally used when discussing membrane physiology?
i dont know :)
Based on Fick’s law, what three factors affect rate of diffusion across a membrane?
- surface area of the membrane
- permeability
- concentration diff of the solute across the membrane (the gradient)
What are each of the components of Fick’s Law?
V - velocity/rate of diffusion
A - surface area of membrane
D - diffusion coefficient
T - thickness of membrane
P1 - partial pressure 1
P2 - partial pressure 2
P1-P2 - gradient
What are the two different mechanisms of membrane transport? What is an example of each?
- active and passive
- diffusion is passive, traveling against the gradient is active because it requires energy
Simple diffusion - 2 types
1 - requires a channel protein, allows the ECF and ICF to be connected
- ions
2 - diffusion goes directly across the membrane w/o a channel
- water, steroids, lipids, gases (nitric oxide)
Facilitated diffusion
- requires a carrier protein that has binding sites on both the ECF and the ICF
- no pores that open
- bigger molecules are transported by this
- glucose, amino acids
Traveling against the gradient is ______?
- active
- uses carrier proteins and only has a site on one side of the ECF or ICF
What is the difference between “passive” and “active” transport?
- passive does not require energy bc its going against the gradient
- active - requires energy because its going against the gradient
How do the kinetics of transport vary for simple vs. facilitated diffusion? What is Vmax?
- facilitated diffusion reaches a maximum velocity before it levels off, simple does not
- maximum velocity of diffusion
What causes Vmax?
diffusion can never be greater than the rate at which the carrier protein can undergo change back and forth
What is ion channel selectivity?
Determines which ions can pass through the channel
What are some mechanisms of selectivity?
- voltage gated - has oppositely charged integral proteins that will draw the ion in
- chemically gated
- size
How does water interact with ions to affect their diffusion through channels?
- ions have to shed their aqueous medium to pass through channels
- could be excluded due to size otherwise
How does the K+ channel exclude smaller charged particles, such as Na+ ?
- Na’s functional diameter is much larger, it has a larger sphere of hydration around it
- Na is too small to interact with the carbonyls that are inside of the pore loops
What is ion channel gating?
regulation of flow of ions in and out of a membrane
What are the three major factors that affect overall net rate of diffusion? (Hint: gradients)
- Chemical gradient – concentration of an ion on either side of the membrane
- Electrochemical gradient – concentration of charge on either side of the membrane – voltage
- Pressure gradient – difference of pressure on either side of the membrane
Hypertonic, Hypotonic, Isotonic
- hypertonic - higher concentration of solutes outside of cell
- hypotonic - lower concentration of solutes outside the cell
- isotonic - same concentration of non-penetrating solute on both sides of membrane
What other factors interact to determine water potential?
- Osmotic potential – determined by solute concentration, the more concentrated the water, the lower the osmotic potential, the higher the solute concentration, the higher the osmotic potential
- Pressure potential – pos or neg pressure acting on a system
- Osmotic pressure – pressure that is required in order to counteract net osmosis of water
Be able to explain in detail the mechanism by which the Na+/K+ pump works
- Two K+ ions bind on the outside of the carrier protein and three Na+ ions bind on the inside
- ATP is cleaved to ADP by ATPase, and the free phosphate is used to cause a chemical and shape change in the carrier molecule
- Change in shape of carrier protein causes it to release 3 Na+ ions to the ECF and two K+ to the ICF
What are the two major types of secondary active transporters?
- both versions of cotransport
- Symport – two diff. solutes are being transport in the same direction
- Antiport – two diff. solutes are being transported in opp directions
