Lipid Digestion Flashcards
what are the 5 classes of lipids?
triacylglycerols phospholipids sphingolipids cholesterol fatty acids
what is the structure of triacylglycerides?
hydrophobic 3 FAs attached to glycerol R1- palmitate R2- oleate R3- oleate or another polyunsaturated FA
what is the structure of phopholipids?
amphipathic 2 FAs and a head group R1- saturated FA 16:0 or 18:0 R2- unsaturated FA 18:1, 18:2, 20:4 head group- hydrophilic -ethanolamine -choline -serine -glycerol -inositol
what is the structure of phingolipids
amphipathic spihngosine backbone FA headgroup -ceramide, phingomyelin glucosylcerbroside lactosylceramide galglioside g2
what is the structure of cholesterol?
giant ring structure
hydrophobic with an OH group
esterfied with a fatty acid on the OH makes it hydrophobic
deca
10 carbons
eicosa
20 carbons
docosa
22 carbons
anoic
0 double bonds
enoic
1 double bonds
delta end
carboxyl end
omega end
methyl end
determines the family
how are unsaturated fatty acids formed?
double bonds added by desaturases that recognize Cs a certain number from the delta end
what sizes of FAs are soluble? insoluble?
soluble- 6-10
insoluble >12
what is a micelle?
single layer of FAs in a sphere
what is a liposome?
double layer of FAs in a sphere
what are the 3 phases of lipid digestion?
phase 1- lipid droplet formation in stomach
phase 2- emulsion droplet formation in small intestine
phase 3- mixed micelle formation
what is the role of bile salts in lipid digestion?
acts as an emulsifier- increases the surface area of the droplets so that they can be broken down by pancreatic enzymes
what is in the mixed micelle?
lipid soluble vitamines
FAs and monoacylglycerols
lysophospholipids
sterols
what are the dietary lipids?
triacylglycerol
phospholipid
sterols (cholesterol, cholesterol ester, sistosterol)
what are the main bile acids?
cholic acid
chenodeoxycholic acid
can be conjugated with either taurine or glycine
what are the digestive enzymes?
lipases
phopholipase A2
cholesterol esterase
what do lipases do?
remove fatty acids from glycerol
forms diacylglycerol and monoacylglycerol
what does phospholipase A2 do?
removes a fatty acid from phospholipids, forming lysophospholipid
what does cholesterol esterase do?
breaks down esterfied cholesterol to free cholesterol by removing a fatty acid
what is the purpose of cholesterol ester?
stored form of cholesterol
what is the purpose of cholesterol?
used in membranes to stabilize transition temperature
which apoprotein is involved in chylomicron synthesis?
ApoB48
what are the components of chylomicrons?
TAG
phospholipids
cholesterol esters
fat soluble vitamins
how do chylomicrons get back into blood?
exit intestinal cell into the lymphatic system
reenter blood at the thoracic duct
what happens to the bile salts in mixed micelles?
absorbed in the ileum (not when the rest of the contents are absorbed)
then returned to liver
5% are lost in the feces (not reabsorbed)
what are the sources of cholesterol?
2/3 serum lipoproteins
1/3 de novo synthesis
what is unique about sistosterol?
not reabsorbed, taken into the cell but released back into lumen
what aids in sistosterol release in the lumen? what are their roles?
NPC1L1- interacts with cholesterol to take it to the chylomicron via conformation change, but takes sistosterol to ABCG5/8 via different conformational change
ABCG5/8- dimer on the apical membrane that returns sistosterol to the lumen
what family is ABCG5/8 a part of?
ATP binding cassette family
requires ATP to move ions, lipids, bile acids, drugs, or peptides
what is sistosterolemia?
abmormal NPC1L1 which takes sistosterol to chylomicron –>sistosterol ends up in the blood
how are different fatty acids absorbed?
chains 14C- lymphatics
which lipids are put into chylomicrons?
all lipids >14C, some 10-12 lengths
what is the advantage of portal vein absorption?
faster- lymph moves very slow
how are lipid malabsorption disorders treated?
give medium chain FAs so they can be absorbed via portal vein
- characterized by lipids in stool
what is ApoB?
apoprotein B
edited version ApoB48 is used in chylomicron synthesis
ApoB100 is used in the liver
how is ApoB48 made?
- transcribed in nucleus
- APOBEC shortens the transcript to 48% of original length
- translated on rER membrane
- associates with chylomicron components in the Golig- forms a chylomicron
what happens to the chylomicron in the blood stream?
- associates with ApoCII/ApoCIII and ApoE
- interacts with with lipoprotein lipase on the surface of tissues
- LPL removes TAGs and breaks them down into free fatty acids to get them into the cell
- ->forms chylomicron remanent with ApoE - chylomicron remanent is recycled by the liver
what do ApoCII/CIII do?
ApoCII- activates lipoprotein lipase
ApoCIII- inhibits lipoprotein lipase
CII/CIII ratio varies with metabolic states
kept on HDL when not being used
what does ApoE do?
tethers the chylomicron to lipoprotein lipase
what happens to glycerol?
goes to liver and used
what is steatorrhea?
severe fat malabsorption due to lack of chylomicron formation from mutation in first 48% of apoprotein gene
what are the symptoms of steatorrhea?
fatty stools- lipids can’t be absorbed because concentration is too high in cells
low serum lipids- lipids get stuck in ER and never make it to blood
how is steatorrhea treated?
medium chain fatty acids in food
skips chylomicrons and are absorbed directly into portal vein
