Membrane Structure

Question 1

Molecular Components of a Membrane

Answer 1

Lipids: form 5nm bilayer, prevent hydrophilic diffusion
Proteins: scattered throughout, transporters and signalers
Carbohydrates: extracellular, function in immune, development, protein folding, virus/toxin binding

Question 2

Membrane Fluidity

Answer 2

Dependent on temperature and composition, highly dynamic with lipids switching places 10^7 times/min and diffusing several mm/sec

Question 3

Parts of a phospholipid

Answer 3

Two hydrophobic fatty acyl chains (16-18 Cs long) attached to a glycerol phosphate backbone via hydroxyl group. Polar head group consists of glycerol, phosphate, and interchangeable group.

Question 4

Types of phospholipids (4)

Answer 4

Phosphatidyl ethanolamine/serine/choline/inositol

Question 5

Parts of Sphingolipid

Answer 5

Sphingosine pairs with fatty acyl chain via amide linkages to form a ceramide. Ceramides have different head groups for different functions.

Question 6

Cholesterol structure

Answer 6

Polar head group attached to rigid steroid ring attached to hydrocarbon tail. Intercalates between lipids and decreases fluidity.

Question 7

Different thicknesses of membranes

Answer 7

Dependent on cholesterol content. Thickness increases with cholesterol content. ER

Question 8

Membrane Asymmetry

Answer 8

Negative phospholipids (serine and inositol) usually intracellular.
PhosCholine, Shpingolipids, and glycolipids extracellular
Cholesterol even distribution

Question 9

Types of membrane associated proteins (3)

Answer 9

Transmembrane: alpha helices, beta sheets, single or multi-pass
Covalent non-trans: anchored cytosolic by amphipathic alpha helix,through covalent attachment to membrane components
Non-covalent: associate w/ membrane through protein-protein interactions

Question 10

Cholesterol Synthesis

Answer 10

Cholesterol obtained in diet or synthesized
Sensor SREBP is in ER (lowest CL concentration) contains bHLH TF for LDLR and cholesterol synthesis.
SREBP is in complex with SCAP and Insig
At low CL, Insig dissociates from SCAP, revealing signaling domain recognized by COPII coat protein.
SREBP/SCAP is moved to Golgi where regulated intramembrane proteolysis occurs by S1P and S2P cleaving SREBP.
bHLH TF is released, LDLR is expressed, 30 enzymes of CL synthesis transcribed (HMGCoA reductase rate limiting)