Membrane structure Flashcards
Do phospholipids spontaneously flip-flop in membranes?
no, they need ATP driven Flippase catalyzes flip-flop
Where are lipids synthesized?
endoplasmic reticulum
What are the three classes of lipids?
phospholipids, sphingolipids, and cholesterol
What is the structure of cholesterol?
a polar hydroxyl group, rigid steroid ring group, and a hydrocarbon tail
What does cholesterol do when it’s in a lipid?
- the steroid ring interacts with the hydrophobic tail of other phospholipids and immobilizes the lipid and decreases fluidity
- lipids are forced to be straightened by cholesterol
- membrane thickness depends on the amount of cholesterol
Does the ER or Golgi have the thicker membrane? Why?
Golgi has the thicker membrane because it has more cholesterol
What does cholesterol uptake depend upon?
- low-density lipoprotein receptor (LDLR)
There is a _________ for cholesterol production.
negative feedback
What is the first and rate-limiting enzyme is synthesizing cholesterol?
HMGCoA - statins block this step
What protein regulates both the LDLR and all 30 of the synthesis proteins?
sterol regulatory element binding protein (SREBP) that holds the transcription factor a basic helix loop helix (bHLH) DNA binding protein
What happens when cholesterol is low?
- Insig no longer binds to SCAP and the SCAP/SREBP complex gets packaged into vesicles to go to the Golgi
- Two step proteolysis (RIP - regulated intramembrane proteolysis) S1P and S2P cut bHLH and it goes to the nucleus (cleavage required by both)
What is RIP been shown critical for?
Notch signaling in development and for cleavage of amyloid precursor protein (APP) to produce the beta amyloid peptide in Alzheimer’s disease
What percentage of ATP energy does Na-K ATPase use?
30%
