Membranes 1 Flashcards
Lipid bilayers are assymetrical. What is a component of lipid bilayers that is found in the external lipid layer? What phospholipid, along with phosphatidylinositol gives the inner lipid bilayer a negative charge?
GLYCOLIPIDS: make up 2-3% of the lipid bilayer and are found on the outside of the lipid bilayer.
Phosphatidylserine: Found on the interior of lipid bilayers. Contributes to the negative charge of the internal layer and is a sign of impending apoptosis when flips to the outside.
What physiological process is beginning when Phosphatidylserines start flipping to the external side of the lipid bilayer?
Apoptosis.
What lipid type is most often found on the outside of the lipid bilayer and, along with cholesterol and proteins, contributes to membrane Rafts?
Sphingolipids
Lipid rafts are functional units. What does this mean?
They have clusters of signaling components, receptors and enzymes that act in a coordinated manner to facilitate many different pathways.
P. gingivalis are able to enter human gingival epithelial cells more because of what membrane structure?
Lipid rafts. Allows P. gingivalis to avoid digestion.
Of the 3 types of transport across membranes, simple diffusion, facilitated diffusion, and active transport, which is able to move substrates against their EC gradient?
ACTIVE TRANSPORT
What are the principles behind Fick’s First Law of Diffusion?
J = -DA(∆c/∆x)
Diffusion across a membrane is proportional to:
1. Area of membrane involved in diffusion
2. Difference in solute concentration on the two sides
J = net rate of diffusion in moles or gram/unit time
D = diffusion coefficient of the solute (Inversely proportional to size of particle and viscosity of solvent.
A = Area of the membrane
∆c = concentration difference across the membrane
∆x = membrane thickness
What two properties would give a solute a LOW diffusion coefficient? If talking about diffusion across a membrane what additional trait affects this?
Large solutes in viscous solvents have the highest diffusion coefficients.
- Remember: “Big globs move slowly through thick muck”
- When dealing with membrane diffusion charge is also important. Large, CHARGED particles will have the slowest diffusion coefficients.
What are the two basic mechanisms by which facilitated diffusion is carried out? What is the structure called that carries each out?
- Carrier Proteins = Enzymes.
- “Ping-pong” conformational change mechanism
- Has Vmax and Km b/c enzyme
- Shows chemical specificity, stereospecificity, and competitive inhibition. - Ion Channels = Protein Pores
- Only conformational change is when the channel is opening or closing.
- Rate of passage is dependent upon EC gradient
What is the difference b/t primary and secondary active transport mechanisms?
- Primary active transport utilizes ATP to generate energy needed to move substrates against their gradients.
- Secondary active transport couples transportation of one substrate against its gradient with another substrate that is moving down its gradient. Doesn’t require a direct energy input.
Ion gradient formation is incredibly important throughout the body to allow signaling. What is the active transporter that is present in ALL animal cells and consumes HALF of all calories eaten? What type of gradient does this pump set up?
The Na-K-ATPase (primary active transport)
- Sets up an electrogenic gradient.
- Forces 3 Na+ (3 positive charges) out of the cell while only transporting 2 K+ (2 positive charges) into the cell.
- This process polarizes the cell membrane.
The ATPase enzyme is located inside or outside of the cell?
The ATPase enzyme is located on the inside of the cell.
- Phosphorylation of the pump causes 3 Na+ to be moved extracellularly.
- Dephosphorylation results in the movement of 2 K+ ions into the cell.
Ouabain is an ATPase inhibitor. What active transport pump does it block? What is the effect?
Ouabain blacks the Na-K ATPase by binding to the extracellular side and not allowing dephosphorylation.
-Slows heartbeat. Previously used clinically but too dangerous.
What important physiological process is stopped when primary active transport pump, H-ATPase, is blocked? Note: stops tooth eruption.
Without H-ATPase functioning, BONE RESORPTION stops.
What is an area in the body where inhibition of H-ATPase can be helpful?
In the stomach stopping H-ATPase can reduce acid reflux. Can help oral health.
