Midterm 2
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Molecules that can cross the membrane (why?)
Small nonpolar (O2, CO2), small uncharged polar (H2O) because inside is np
Molecules that cannot cross the membrane (why?)
Large and uncharged (glucose) or charged (K+) because inside is np
What are the four types of transport mechanisms? Examples?
Simple diffusion, facilitated diffusion, passive mediated diffusion, and active transport. In order, O2, Na+, Glucose, Na+/K+ pump
What is the common structural characteristic of transporters?
integral membrane proteins
What is the structure of the K+ channel? What kind of transport? What direction?
M1 and M2 helix, selectivity filter made of P segment, lined with carbonyl. Moves in to out.
How does the K+ channel select for K+? Why not Na+?
The selectivity filter is 3 angs. K+ is 2.7 angs, only K+ fits.
What is the role of the “plug” in the K+ channel? What does the voltage sensing S4 domain do?
The plug keeps K+ from flowing through. The S4 domain senses positively charged AAs and transmits signal to open.
What kind of transport is the Na+/K+ pump? How does it work, and does it have a refractory period?
Active transport, conformational changes let 3 Na+ out and 2 K+ in. Refractory period (1-2 ms) to even out charges.
How do conformational changes occur in Na+/K+ pump?
Phosphorylization
Why are myelin sheaths and nodes of ravier important?
Both allow charges to jump from nodes, meaning fast response times.
What is the direction of propagation? why doesn’t action potential move backwards?
Dendrites -> cell -> axon. Can’t move backwards because synaptic vesicles are only at the axon end.
How do charges change down the axon during refractory, action, and depolarization potentials?
Resting axon is - inside and + outside. Action potential (depolarization) is + inside and - outside. Na+ then K+ open.
How does the axon communicate with it’s target?
Via neurotransmitters
What are neurotransmitters role? How are they packaged?
Communicate from neuron to neuron. Packaged in synaptic vessicles
What is the difference in synaptic vesicles in a presynaptic and postsynaptic cell?
Vessicles piled in pre, post waiting to recieve them ig
What is ACh and Neurepenephrine?
neurotransmitters
What does ACh stimulate or inhibit? What step in the ACh ligand gated channel determines this?
Causes either Na+ gates to open or Cl- gates to open by binding to receptor.
What ion gate helps with neurotransmitter release?
Voltage gated Ca2+ channel
What are the 6 steps of releasing ACh? How does this relate to action potential?
Nerve impulse -> Ca2+ channel opens -> ACh released -> ACh binds to receptor -> Na+/Cl- gates open -> nerve impulse. Relates because it is the result of and it creates an action potential.
What’s the difference in rate of diffusion in facilitated vs simple diffusion?
Simple is slow, facilitated is fast.
What provides energy to the Na+/Glucose cotransporter?
Powered by Na+ gradient.
How does glucose move from the intestinal lumen to the bloodstream?
Into cell by Na+/Glucose cotransporter, active transport, powered by Na+ gradient, and out of cell into bloodstream by GLUT2 facilitated diffusion
What is endosymbiosis? Which organelles are related?
An organism in an organism. Mitochondria.
How do new organelles generate? Exceptions?
Made by cellular DNA, except for mitochondria/chloroplasts