PSL-Week 1 Flashcards
What does permeability depend on?
molecular size, lipid solubility, and charge
What are characteristics of simple diffusion?
allow movement of small, lipid soluble molecules and gases through phospholipid bilayer or pores
movement is down its concentration gradient
passive as no energy is required
What differentiate facilitated diffusion from simple diffusion?
in this type of diffusion, the molecules pass through with assistance from carrier protein
however, it is similar to simpel diffusion as movement is down its concentration gradient and no energy is required
What does saturation mean in facilitated diffusion?
since the substances require assistance of carrier proteins, the amount of molecules to transport can exceed than amount of available transporters which means that the transporters are saturated and adding more molecules won’t increase transport.
What are differences and similarities between active transport and secondary active transport?
similarities: both move substances against their concentration gradient, both require energy
differences: energy for primary transport comes from ATP hydrolysis while secondary active transport is powered by chemical energy in substance diffsuing down its [ ] gradient to push other substance agiant its [ ] gradient
What makes channels different from pores?
channels are made from memebrane spanning proteins with pore loop that create selectivity and contain an S4 segment in teh 4th transmembrane protein
What are gated channels and their two types?
are channels which are closed off by branch of protein structure that act as gate and when it opens it has selectivity on what it allows through
There are 2 types: ligand and voltage gated
What are ligand gated channels
also known as cell membrane receptores which are important in synaptic transmission and once they get bound by ligand, they trigger events like activation of enzyme
What are voltage gated channels?
memebrane channels which are sensitive to potential memebrane difference which causes conformation changes in channel to create a difffusion pore
Endocytosis vs Exocytosis
endo- is the inward pinching of memebrane to create vesicle which is usually receptor mediated to capture proteins from out to in
exo- partial or complete fusion of vesicles with cell memebrane for bulk trans memebrane transport of specific molecules from in to out
What are the two types of exocytosis and how do tehir mechanism differ?
Exo 1- more rapid mechanism which is known as kiss and run
Exo 2- full exocytosis
in Exo 1- the vesicle will dock and fuse with membrane at locations called fusion pores and will connect and disconnect several times until it empties the vesicle completly
in Exo 2- complete fusion of vesicle with membrane and release of contents at once
What are the two conditions to generate memebrane potential?
1- create [ ] gradient by having ion pump actively transport certain ions
2- semipermeable membrane to allow one ion specie to diffuse more than others
Why are Na’K pump essential and found in all cells?
it creates that memebrane potential as it has Na/K dependent ATPase enzyme which moves 3 Na out for 2 K in
When does resting membrane potential occur?
when there is electrochemical equilibrium reached
What is electrochemical equilibirum?
when the electrial work that is repelling cation, K, out is equal to the chemical diffusion down [ ] gradient
What is nernest equation?
in ideal situation, it describes the balance between chemical work of diffusion with electrical repulsion to give potential difference across memebrane and only valid when and only for when there is one ion specie diffusing across memebrane.
Why is membrane potential -70 mV and not -90 mV as calculated from nernest equation?
even though membrane is most permeable to K at rest the other ions, Na and Cl, are still somewhat diffusing
What is the equation that can help us calculate the membrane potential by taking into consideration the relative permeability?
Goldman equation which is a form of exapnded Nernest equation
How is Cl- ions concentration distribution different from K and Na?
Cl ions is more concentrated outside than inside due to existance of anions inside the cell that are impermeable and only leave by exocytosis so the negative inside repel the chlorine and not the active pumps like Na/K pumps
What is a characteristic for Na channnels that distinguish it from rest?
the channel has two gates: Activation gate and inactivation gate
How do the two gates open and close as membrane potential changes?
at rest, when the MP is -70, the activation gate is closed while the inactivation gate is swinging freely and no Na is allowed through, as the MP changes and reaches the threshold of -55, the activation gate opens and allows Na in while the inactivation gate waits 0.5 ms to start closing. The period in which the inactivation gate is waiting, this will allow Na to enter and reach +30 MP before the inactivation gate starts closing up.
When does the inactivation gate gets removed?
when the MP must go below threshold level
What does existance of Na channels in great amount in cell membrane tells us about that cell?
that the cell has an exciatble membrane and when the Na channel opens, MP urges to reach +60 mV but the existance of inactivation prevents that and by Na channels inactivated, the only main current is K leakage
How come the opening of voltage gated channels of both Na and K when teh threshold of -55 have been reached only has Na entering more than K leaving and depolarizing the cell?
that’s because the opening of Na channels occur faster than K so by the time K voltage gated channels open, the Na channels have allowed enough Na in to depolarize cell to +30
