Lipids

Question 1

membrane composition

Answer 1

Lipids: phospholipds (sphingolipids (SM), PC, PE, PS, PI), cholesterol, glycolipids
Proteins (specific to membrane type)

Question 2

Lipid/protein content in different membranes

Answer 2

• variable between different membranes
• constant for specific membrane

Myelin: 75% lipid, 25% protein
RBC: 40% lipid, 60% protein
IMM: 20% lipid, 80% protein

Question 3

RBC plasma membrane lipid types

Answer 3

40% lipids:
cholesterol 15%
phospholipids 25% (mostly PC and SM since they’re choline lipids)

50% of lipid mass is unsaturated fatty acids

Question 4

amphipathic

Answer 4

has both hydrophobic portion and hydrophilic portion

Question 5

temperature/fluidity and phospholipid bilayer

Answer 5

• affected by fatty acid chain length and degree of unsaturation
• longer chain=higher melting temperature
• more unsaturation=lower melting temperature

Question 6

Cholesterol in bilayer

Answer 6

• modulates membrane fluidity

- -OH on outside of membrane

Question 7

Lipid distribution on cytoplasmic vs extracellular layer of bilayer

Answer 7

• asymmetric distribution of lipid types on inside and outside
• lipids can diffuse along same layer (lateral) or can move from inner to outer or from outer to inner (transverse)

Question 8

protein flipase

Answer 8

can aid in transverse movement of phospholipids from one side of bilayer to the other

Question 9

RBC plasma membrane inner/outer lipid distribution

Answer 9

-inner mostly PS and PE
-Outer mostly PC and SM (choline containing)
More choline on outer surface

Question 10

Integral/intrinsic proteins

Answer 10

• detergents to isolate
• hydrophobic
• structural role
• pumps/transporters, receptors, enzymes

Question 11

Peripheral/Extrinsic proteins

Answer 11

• pH, ions to isolate
• hydrophilic
• enzymes, cytoskeletal protein

Question 12

RBC proteins

Answer 12

• isolated after osmotic shock
• Extrinsic/peripheral proteins: spectrin, ankyrin, actin, band 4.1 and 4.2
• intrinsic/integral: band 3 (anion transport), glycophorin, G3PD

Question 13

Glycophorin

Answer 13

• first membrane protein ever sequenced
• antigen
• abundant in RBC
• N terminal 70aa outside cell with sugars
• 23 apolar aa in transbilayer domain
• 38aa at c terminus is internal charged domain

Question 14

Width of bilayer

Answer 14

35A
23amino acids
(1.5A is rise/residue of alpha helix, 1.5*23=~35A)

Question 15

plasma lipoproteins

Answer 15

• complex of lipids and specific proteins (apolipoproteins)
• used to solubilize fat and transport in blood
• 4 major types: chylomicrons (CM), very low density (VLDL), low density (LDL), high density (HDL)

Question 16

FA storage

Answer 16

• FA stored at triglygerides
• TG broked down into FA and glycerol by lipase
• FA uptake by cell
• FA used as energy, stored, restored back to TG, or beta oxidized

Question 17

Cholesterol ester

Answer 17

• for storage/transport of cholesterol

- cholesterol coupled with FA to make cholesterol ester

Question 18

CM composition/location

Answer 18

• 90% TG
• B, C, E apoprotein classes
• 2000A big
• from intestine
• removed from blood in adipose tissue/liver

Question 19

VLDL composition/location

Answer 19

• 65% TG
• B, C, E apoprotein classes
• 600A medium sized
• from liver
• removed from blood in adipose tissue

Question 20

LDL composition

Answer 20

• 50% CE
• B class apoprotein
• 200A small
• from VLDL catabolism
• removed from blood in liver and peripheral cells

Question 21

HDL composition

Answer 21

• 20% CE, 25% PL, 50% protein
• A class apoprotein
• 100A very small
• from liver and removed from blood in liver

Question 22

LDL function

Answer 22

cholesterol delivery (bad)

Question 23

HDl function

Answer 23

for cholesterol removal from cells and body (good)

Question 24

Lipoprotein lipase (LPL)

Answer 24

• plasma enzyme
• breaks TG into FA
• Apo-C is coenzyme

Question 25

Lechithin cholesterol acyl transferase (LCAT)

Answer 25

- plasma enzyme - takes FA from phospholipid to make CE - Apo A is cofactor in bloodstream

Question 26

Acyl-CoA cholesterol acyl transferase (ACAT)

Answer 26

takes acyl-CoA and cholesterol and makes CE | inside liver cells

Question 27

HMG-CoA reductase

Answer 27

makes cholesterol, rate limiting step in cholesterol synthesis regulates body cholesterol

Question 28

Apolipoproteins

Answer 28

- Apo A: LCAT cofactor, ligand for ABC-A1 and SRB1 - Apo B: ligand for LDL receptor - Apo C: LPL cofactor

Question 29

Biological microemulsion

Answer 29

droplet of fat (TG/CE) at core, coated with phospholipid monolayer dotted with apolipoproteins for stability and enzymatic function

Question 30

Cholesterol in the liver

Answer 30

Cholesterol synthesis (FA-->TG) some cholesterol --> CE some cholesterol --> bile (only way to remove from body)

Question 31

Familial hyperchosesterolemia

Answer 31

genetic disease resulting in inability of cells to take up cholesterol by LDL and high cholesterol in bloodstream

Question 32

Receptor mediated endocytosis

Answer 32

- LDL receptors cluster causing 'fatty coat' on outside of cell - clatherin coat formed and makes invagination of plasma membrane - vesicle endocytosed, merge with endosome to disocciate receptor/LDL - receptors recycled to cell surface - Apo B and CE broken down in lysosome to aa and cholesterol/FA respectively - cholesterol used for membrane biogenesis, steroid hormones (in adrenal gland), bile acids (in liver) or put in storage as CE (via ACAT) which turns off HMG-coa reductase and stops cholesterol synthesis

Question 33

Reverse cholesterol transport

Answer 33

Only method of cholesterol removal - ABC-A1 transports cholesterol and PL out of peripheral cell (with Apo A as ligand) - LCAT converts cholesterol to CE in nascent HDL - mature HDL formed - CE selectively taken into liver cell by SRB1 (using apo A as ligand) - CE in liver to bile acid synthesis or secreted into bile for removal.