Flashcards in Week 2 - Cell Structure - Holy Deck (71)
Holy emphasized that the inner part of the organelle was most similar to what?
The extracellular space
List a few functions of cell membranes:
There are more...
What are the 3 important functions of cholesterol?
-They inhibit phase transitions.
This means that they can behave more uniformly despite changes in temperature or other similar disturbances.
(i had never heard this before, so i thought it might be important to explain)
Estimated number of differnt eukaryotic membrane proteins:
What is the structure of a glycolipid
It is a lipid with a sugar group added.
Holy emphasized that these are relatively small oligosacharides that are added compared to the ones we will see on proteins
What are the 4 major phopsholipids?
Where are they synthesized and how do they travel?
Phosphatidyl-Ethanolamines, -serines, and -cholines
(Made in the ER, transported by membrane flow)
(Made in the golgi and transported by membrane flow)
Functions of glycolipids:
Protection - Glycocalyx!
Create surface properties of membranes
(Can also be an entry point for toxins, like cholera)
How are phosphatidylinositol phospolipids involved in cell signaling?
Well they stick out of the membrane surface and they can be bound to and activate various enzymes
PI phospholipds can serve as a substrate for membrane associated phospholipids.
An example is the G-prot-coupled receptor/DAG/IP3 pathway
Flippases do what?
Flip phospolipids between opposite leaflets
How are phospholipds assymetrically ditrsibuted in different cellular membranes?
Initially distribution is even but what happens is that phosphocholine and sphingomyelines are flipped to the non-cytosol side.
The cytosolic leaflet, as a result, is enrisched with phosphatidylethanolamine and phosphatidylserine
To signal macrophages to destroy the cell, how do you change the phospholipid distribution?
Move a bunch of the phosphatidl serines to the non-cytosolic side!!!
Most transmembrane proteins have what structure?
but some are crazy beta barrels
Where are the sugar groups on the cell membrane and why?
The non-cytosolic side, because thats how they re made. Also its important to function.
What is the function of the glycocalyx?
Most mem. proteins are glycosylated!
4 methods to organize proteins in a membrane:
-self assembly into aggregates
-tether to extracellular molecules
-tether to intracellular molecules (cytoskeleton)
Bind to adjacent proteins for cell-cell junctions
What is the main protein that forms the critical architecture for red blood cells?
(actin has shrunk down to be way less important)
Important integral protein for cell-cell adhesions
need Ca to function
Where are integral proteins made?
Where are cytosolic proteins made?
The cytosol, on free ribosomes not attached to the ER at all!
How can smooth ER adjust to personal needs?
Can actually expand or shrink depending on detox needs. Like alcoholics have big expanded smooth ER's
Interesting that sometimes the most toxic compunds are produced while trying to detox other compunds.
Like dogs and antifreeze!
3 functions of smooth ER
What actually determines whether a polyribosome becomes attached to an ER membrane or remains free-floating in the cytoplasm?
The information is actually coded within the emrging polypeptide itself. Crazy right?
(Its called an ER signal sequence, in the absence of the signal it will remain free-floating)
List the steps of a ribosome attaching to the ER membrane to feed the peptide through:
1 - polypeptide signal sequence (attached to the ribosome and mRNA) bind to signal recognition particle (SRP)
2 - the SRP receptor on the ER membrane binds and anchors in the mRNA-ribosome-SRP complex
3- The complex displaces the SRP and attaches to a translocator
4- The translocator has a pore where the peptide can be fed through the membrane
The number of times a protein dips through the membrane depends on the number of ___________
stop transfer sequences
Proteins made in the ER undergo what kind of glycosylation?
How does N-linkage work?
14-sugar oligosacchardide is added to a lipid called a dolichol, then this is added to the polypeptide later as it is being spooled into the ER lumen
What are proteoglycans
A special calss of HEAVILY-glycosylated proteins
The protein itself is made in the ER, but the o-linked glycolation occurs in the Golgi
Also remember this is O-linked glycosylation!!!!!!!
What is the purpose of proteogylcan sugars being sulfated and negatively charged?
They can attract cations and water, which creates a sort of gel-like extracellular area. I don't exactly know what is so great about that...
What should happen to misfolded proteins?
ubiquitinated and destroyed by proteosomes!