Membrane Structure & Function
What are the 4 main functions of the plasma membrane? (Other than helping the cell hold its structure)
1. receiving information
2. capacity for movement and expansion
3. import/export of small molecules
4. use transport proteins to allow certain things in
What is the function of Spectrin?
helps form the cortex- which is a mesh of filamentous proteins that supports the PM and gives the cell shape
Describe passive, facilitated, and active transport
P: movement down the concentration gradient; no ATP needed
F: type of passive transport with use of transporters; the transporters randomly switch conformation
A: movement against the conc. gradient; ATP needed
What are the 2 main characteristics of a neuron?
Irritability- ability to alter membrane potential in response to stimuli
Conductivity- ability to transmit electrical impulses
What are the major features of a neuron?
dendrites
cell body (soma)
axon
hillock
axon endings
What are all the way lipids can move within the membrane and describe them? (4 of them)
1. flexion- the fatty acid tails "wag" back and forth: very fast
2. rotation- lipid spins around axis: very fast
3. lateral diffusion- lipid switches spots with lipid next to it: fast
4. transverse diffusion- the lipid flips to the other side of the PM: slow and needs protein help
What are the characteristics of glycocalyx and lectin?
G: thin sugar layer that is formed from sugar binding to water; allows cells to squeeze through PM and protects cells
L: proteins that bind to sugar; allow WBCs to bind blood vessel walls near infection
What is resting membrane potential?
the difference in ion conc. across the membrane leads to voltage diff.
negative intracellular; positive extracellular
What is a synapse?
how neurons communicate with each other- AP reaches synapse in one neuron which results in the fusion of synaptic vesicles
Describe the 2 VGC responsible for generating action potentials
The channels open and close in response to voltage changes and are present in the axon
K+: slow to open and close- hyperpolarization
Na+: fast open and open- depolarization
How does cholesterol and desaturases help with membrane fluidity when the temperature drops?
C: keeps the fatty acid tails from packing together and freezing
D: these enzymes convert single bonds to cis double bond in the tails which creates "kinks" and increases fluidity
What is the rate of diffusion dependent on?
1. level of concentration difference
2. permeability
3. surface area
4. charge
What are the characteristics and types of ion channels?
they are selective to ensure only ions pass and gated meaning they open and close
voltage-gated, ligand-gated, mechanically gated
Local Potential vs. Action Potential
LP: small stimuli lead to small depolarization of membrane, but quickly returns to resting mem. potential- Na+ VGC in cell body and dendrites open
AP: mem potential hits threshold and LARGE increase in mem potential occurs- Na+ VGC in hillock open
How does the Ca2+ VGC support synapses?
when the AP arrives at the terminal of the presynaptic nerve it causes Ca2+ VGC to open which results in the fusion of vesicles with the terminal
this releases the neurotransmitters that were in the vesicles
Scramblase vs. Flippase?
S: randomly flips lipids from cytosolic leaflet to the exoplasmic; no ATP needed; works in the ER; does this so both monolayers grow evenly
F: selectively moves specific lipids to different leaflets (ex. glycolipids on exo leaf, cholesterol on both, and PI and PS on the cyto leaf); slow process that needs ATP; works in Golgi
What can help facilitate osmosis even more?
Aquaporins
Channels vs. Transporters
C: Pores that can be open or closed and discriminate based on size and charge
T: bind to specific molecules and undergo a conformational change to transport each
Many different types of each and both can be used for either passive or active transport.
How are voltage-gated channels related to action potentials?
the increase in membrane potential to the threshold causes VGC to open which results in the influx of ions into the neuron which further increases potential causing the AP
How are the neurotransmitters released by the synaptic vesicle an example of ligands and what is the reason for them?
they bind to a receptor in order to open a gated ion channel
when the neurotransmitters bind to the LGC it opens so ions can flow into the postsynaptic neuron which causes a change in membrane potential
causes depolarization and the AP travels throughout cells
Summarize Gorder and Grendell's experiment and findings
-extracted membranes from red blood cells to calculate the surface area of the RBCs and the "floated" lipids
-discovered PM is a lipid bilayer because of 2:1 monolayer to cell ratio (since cell is bilayer the SA is half compared to when cell monolayer is spread).
-head is hydrophilic and tail is hydrophobic= amphipathic
Describe a hypo, hyper, and isotonic solution and what it does to a cell
Hyper: solution has more solute than the cell and water leaves the cell causing it to shrink
Hypo: solution has less solute than the cell and water enters the cell causing it to grow
Iso: solution has equal solutes to cytoplasm so there is no net diffusion and no size change
What is a gradient driven pump and an example
movement of 1 solution down their conc. gradient moves another solute up its gradient: type of active transport
Na+/Glucose symport
On a graph of an action potential when are Na+ VGC open, closed, and inactive?
at rest the channels are closed
when potential hits threshold to reaching AP the Na+ VGC are open
they become inactive when potential begins to drop again
closed when return to rest
How does Acetylcholine affect us?
type of neurotransmitter that when binds to the receptor causes depolarization
this allows for muscle contraction