Lipid Digestion Flashcards by Christina Provenza

what are the 5 classes of lipids?

triacylglycerols
phospholipids
sphingolipids
cholesterol
fatty acids

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what is the structure of triacylglycerides?

hydrophobic
3 FAs attached to glycerol
R1- palmitate
R2- oleate
R3- oleate or another polyunsaturated FA

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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

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what is the structure of phingolipids

amphipathic
spihngosine backbone
FA
headgroup
-ceramide, phingomyelin
glucosylcerbroside
lactosylceramide
galglioside g2

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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

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deca

10 carbons

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eicosa

20 carbons

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docosa

22 carbons

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anoic

0 double bonds

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enoic

1 double bonds

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delta end

carboxyl end

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omega end

methyl end

determines the family

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how are unsaturated fatty acids formed?

double bonds added by desaturases that recognize Cs a certain number from the delta end

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what sizes of FAs are soluble? insoluble?

soluble- 6-10

insoluble >12

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what is a micelle?

single layer of FAs in a sphere

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what is a liposome?

double layer of FAs in a sphere

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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

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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

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what is in the mixed micelle?

lipid soluble vitamines
FAs and monoacylglycerols
lysophospholipids
sterols

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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?

1. transcribed in nucleus 2. APOBEC shortens the transcript to 48% of original length 3. translated on rER membrane 4. associates with chylomicron components in the Golig- forms a chylomicron

what happens to the chylomicron in the blood stream?

1. associates with ApoCII/ApoCIII and ApoE 2. interacts with with lipoprotein lipase on the surface of tissues 3. LPL removes TAGs and breaks them down into free fatty acids to get them into the cell - ->forms chylomicron remanent with ApoE 4. 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