Midterm 2 Difficult Topics Flashcards
(37 cards)
lipid shape that forms micelles? bilayers?
single tail/cone, double tail/cylinder
why do membranes need cholesterol?
it decreases local membrane fluidity by tightly binding adjacent hydrocarbons close to the polar head
how it cholesterol like antifreeze?
prevents membrane from freezing when temps are low, but prevents it from boiling when temps are high
cytosolic leaflet lipid ratios vs extracellular leaflet lipid ratios
phosphatidylserine stays on exterior side but flips to cytosolic during apoptosis (to signal that it needs to be eaten)
ATP dependent flippases cover hydrophilc head group so the lipid can pass through hydrophobic interior to other leaflet
Why are hydrophobicity plots bad at detecting beta barrels?
The amino acids in a beta barrel alternate hydrophobicity every other, it won’t show up on this test
why should you use non ionic detergent to remove proteins from a membrane?
they are polar but not charged, so they bind to hydrophobic residues and outcompete the bound surrounding lipids while stabilizing the protein (need lots of detergent to achieve)w
why do lysosomes have a ~100x higher H+ concentration inside them?
The high pH in lysosomes supports its acid hydrolases, enzymes that break stuff down can only funciton at highly acidic pHs
is GLUT1 (and other uniporters like it) saturable?
Yes: Vmax (max transport rate) limited by number of transport protein
What does digoxin do? why is this bad if you’re healthy but good for weak hearts?
suppressed sodium ATPases which indirectly makes cells worse at pumping out calcium
it’s good for weak hearts because they need the calcium for muscle contraction
MRD1 cancers
tumor cells that express ABC transporters can pump out more of the anti-cancer and chemo drugs resulting in patients with MRD1 cancers (fitness advantage for tumor cells)
what makes y spin in ATP synthases?
a steep proton gradient made with the ETC drives the proces and F0 acts as a merry. go round with the aspartate acting as the H+ carrier… arginine (+ charged) swings between H+ entry and exit sites and is displaced by the incoming proton which facilitates exit of outgoing proton
what causes cells cytoplasmic calcium concentration to change?
plasma membrane channels let calcium ion in or ER channels released of of their stored calcium to the cytoplasm
how do we know what ER looks like?
transmission electron micrographs
do secretory proteins enter the ER lumen?
What experimental techniques proved this?
YES
give pancreatic cells radioactive leucine (labels newly synthesized proteins) then isolate rough microsomes from density technique… treat samples with and without detergent then add proteases to all samples; if proteins are in the ER, protease can’t digest them without detergent, will digest with detergent
proteins not in ER digest regardless of detergent presence
how would you determine whether proteins are co translationally inserted into the ER?
run samples of protein synthesis with one with microsomes containing ER that was added after and one with microsomes containing ER that was there from the start… if proteins from both samples end up in the ER, they are inserted after translation (no cotranslationally) and if proteins from the sample containing microsomes from start then they are inserted co translationally
Functions of sec61 translocon
helps polypeptides cross the ER membrane
enables TMDs to pass sideways through walls and guides proper orientation
binds to and releases ribosomes
has tight seal preventing things (ATP or calcium) from leaking
what does BiP do in co translational insertion?
acts as a clamp to pull the peptide into the lumen –> molecular ratchet
single pass transmembrane proteins into ER membrane
nascent polypeptide in translocon, N terminal signal sequence is cleaved
new n terminus is now in ER lumen
TMD in polypeptide stops it from going through the translocon (transfer stopped)
TMD slips through translocon walls into lipid bilayer where it is anchored and translation resumes
remaining c terminal domain now in cytosol with the rest of the translated protein
What if a nascent polypeptide does not have an N terminal signal sequence?
secondary rules
SRP recognize internal hydrophobic sequence and brings it to the translocon
Sec61 looks for positive charges in polypeptide adjacent to hydrophobic TMD
the side with adjacent + charges will be oriented to remain in the cytosol and side without will be oriented to be in ER lumen
hydrophobic TMD slips through translocon’s walls to be anchored in the lipid bilayer (no cleavage)
what about when a polypeptide is being cotranslationally inserted into the ER without an N terminal signal sequence and with 2 TMDs?
Translocon encounters the first hydrophobic TMD and orients it based on positive charges, translation continues, translocon encounters second hydrophobic TMD and passes it to lipid bilayer (without orienting it)
rest of peptide is translated in the cytosol
what happens when a polypeptide is being co translationally inserted into the ER without an N terminal signal sequence and with three or more TMDs?
follows same pattern as with 1 or 2 TMDs
first TMD provides orientation
every TMD after the first is put straight into the membrane without additional orientation
how are tail anchored proteins co translationally inserted into the ER?
TMD at c terminal but too late for SRP recognition…
interacts with Get3 ATPase complex and a distinct translocon, Get3 hydrolyzes 2 ATP to ADP to stick the c terminal hydrophobic TMD in the ER membrane (rest of protein remains in cytosol)
how are GPI anchored protein co translationally inserted in the ER?
protein starts with cleavable N terminal signal sequence and c terminal TMD, N terminal signal sequence is cleaved by translocon then c terminal TMD anchors it in membrane… instead of staying there the c terminal TMD is cleaved and protein is linked to GPI anchor
what does the GPI anchor allow for in the membrane?
Increased mobility
