Lipid digestion is __ in the mouth and stomach; lipids are __ to the small intestine __.
- essentialy intact
mixing of two normally immiscible liquids (fat and water) to increase the surface area of the lipid, permitting greater enzymatic interaction and processing; aided by bile
contains bile salts, pigments, and cholesterol
secreteed by the liver and stored in the gallbladder
Pancrease secretes what to hydrolyze lipids?
pancreatic lipase, colipase, and cholesterol esterase
water-soluble spheres with a lipid-soluble interior; vital in digestion, transport, absorption of lipid-soluble substances starting from teh duodenum all the way to the end of the ileum
Where are micelles absorbed?
at the brush border of teh intestinal mucosal cells, where they are absorbed into teh mucosa and re-esterified to form triacylglycerols and cholesteryl esters and packaged into chylomicrons
Chylomicrons leave the intestine via __, the vessels of teh lymphatic system, and re-enter the bloodstream via the __, a long lymphatic vessel that empties into the left __ at the base of the neck.
- thoracic duct
- subclavian vein
In the postabsorptive state, what happens?
fats are released from adipose tissue and used for energy
Although human adipose tissue does not respond directly to glucagon, a fall in insulin levels activates a __ that hydrolyzes triacylglycerols, yielding __ and __.
__ ad __ can also activate HSL.
- hormone-sensitive lipase
- epinephrine and cortisol
Released glycerol from fat may be transported to theliver for _ or __.
glycolysis or gluconeogenesis
necessary for teh metabolism of chylomicrons andVLDL
it is an enzyme that can release free fatty acids from triacylglycerols in these lipoproteins
How are free fatty acids transported through the blood?
in association with albumin, a carrier protein
How are triacylglycerol and cholesterol transported in the blood?
as lipoproteins: aggregates of apolipoproteins and lipids
transport dietary Triacylglycerols and cholesterol from intestine to tissues
transport triacylglycerols from liver to tissues
pick up cholesterol from HDL to become LDL; picked up by the liver
deliver cholesterol into cells
- pick up cholesterol accumulating in blood vessels
- delivers cholesterol to liver and steroidogenic tissues
- transfers apolipoproteins to other lipoproteins
Some IDL is what?
reabsorbed by the liver by apolipoproteins on its exterior, and some is further processed in the bloodstream
It is thus a transition particle between triacylglycerol transport (associated with chylomicrons adn VLDL) and cholesterol transport (associated with LDL and HDL)
HDL contains __ used for __.
cholesterol recovery, that is, teh cleaning up of excess cholesterol from blood vessels for excretion
What are apolipoproteins?
receptor molecules and are involved in signaling
an enzyme that catalyzes cholesterol esterification
activated by HDL apoproteins
adds a fatty acid to cholesterol to produce soluble cholesteryl esters
Explain de novo synthesis of cholesterol.
it occurs in the liver and is driven by acetyl-CoA adn ATP
The citrate shuttle carries mitochondrial acetyl-CoA into teh cytoplasm, where synthesis occurs, using NADPH as a reducer
RLS in cholesterol synthesis
synthesis of mevalonic acid in the SER; catalyzed by HMG CoA reductase
What promotes cholesterol synthesis?
facilitates the transfer of cholesterols from HDL to LDL
What are two important essential fatty acids?
alpha-linolenic acid and linoleic acid
both are polyunsaturated fatty acids
What does the omega in the omega numbering system indicate?
the position of the last double bond relative to teh end of the chain
Where does fatty acid biosynthesis occur?
Where are its products transported?
in the liver
to adipose tissue for storage
What are teh two major enzymes of fatty acid synthesis?
- acetyl-CoA carboxylase
- fatty acid synthases
What is the primary end product of fatty acid synthesis?
palmitic acid (palmitate)
Int he cytosol, if there is an accumulation of citrate, what can happen?
citrate lyase splits citrate back into acetyl-CoA and OAA, the latter of which can return to teh mitochondrion to continue moving acetyl CoA
activates acetyl-CoA in the cytoplasm for incorporation into fatty acids
rate limiting enzyme of fatty acid biosynthesis
activated by insulin and citrate
fatty acid synthase (aka: palmitate synthase)
palmitate is teh only fatty acid that humans can synthesis de novo; in teh cytosol; induced after a meal high in carbs due to elevated insulin levels
contains an acyl carrier protein and uses NADPH
Explain production of palmitate
eight acetyl-CoA groups are required to produce it.
steps involve: attachment to ACP, bond formation between activated malonyl CoA and teh growing chain, reduction of carboxyl group, dehydration, reduction of the double bond
branched chain fatty acids undergo this
occurs in ER to produce dicarboxylic acids
What number chain fatty acids can't diffuse freely into the mito?
14 to 20 carbons; they require the carnitine shutle
repetition of four steps
each four step cycle releases one acetyl-CoA adn reduces NAD+ and FAD, which are oxidized int eh ETC, producign ATP
- 1) Oxidation of fatty acid to form a double bond
- 2) Hydration of double bond to form hydroxyl grou
- 3) oxidation of hydroxyl group to form carbonyl
- 4) splitting into shorter acyl CoA and acetyl CoA
DIn muscle and adipose tissue, acetyl-CoA does what?
enters the CAC
In the liver, acetyl-CoA does what?
stimulates gluconeogenesis by activating pyruvate carboxylse because it can't be converted to glucose
In a fasting state, the liver does what?
produces more acetyl-Coa by beta ox than is used in the CAC. The acetyl CoA is then used to synthesize ketone bodies
Difference between odd number fatty acids and even numbered?
durign the final cycle, odd-numebred fatty acids yield one acetyl-CoA and one propionyl-CoA, which is converted to methylmalonyl-CoA-->converted to succinyl CoA
What must unsaturated fatty acids undergo?
they rearrange cis double bonds at the 3,4 position to trans double bonds at the 2,3 position
For conjugated double bonds, what must happen?
2,4-dienoyl-CoA reductase converts two conjugated double bonds to just one double bond at the 3,4 position
In the fasting state, the liver converts excess acetyl-CoA from beta ox of fatty acids intot eh __.
ketone bodies acetoacetate adn 3-hydroxybutyrate, which can be used for energy in various tissues
What can cardiac tissue do with the ketones?
can metabolize it to acetyl-CoA
After a week of fasting, ketones reach a concentration in the blood that is high enough for the __.
brain to begin metabolizing them
occurs in the mito of liver cells when excess acetyl-CoA accumulates in the fasting state
During ketolysis, what happens to 3-hydroxybutyrate?
it is oxidized to acetoacetate
Ketolysis in the brain
brain derives 2/3 energy from ketone bodies, metabolizing it to acetyl-CoA, inhibiting pyruvate dehydrogenase
glycolysis and glucose uptake in the brain decreases
Absorption of amino acids and small peptides through the luminal membrane is accomplished by __.
secondary active transport linked to sodium
glucogenic amino acids
can be converted into glucose through gluconeogenesis
all but leucine and lysine
ketogenic amino acids
can be converted into acetyl-CoA and ketone bodies
Leu, Lys, Isl, Phe, Thr, Trp, Tyr