Lipolysis, Fatty Acid Oxidation, and Ketogenesis Flashcards
describe lipolysis within an adipocyte
3 sequential enzymes:
adipose triglyceride lipase (ATGL)
hormone sensitive lipase (HSL)- DG lipase
monoglyceride lipase (MG)-
ATGL and HSL are highly regulated.
HSL uses perlipin
lipoprotein lipase
produced within adipocytes, is expressed on the surface and acts on circulating TGs to convert them to FAs for uptake
pancreatic lipase
responsible for hydrolysis of ingested TGs in the small intestine
free fatty acids
fatty acids circulating in plasma or bound to albumin. available as oxidative fuel
where does fatty acid oxidation take place?
in the mitochondria of all cells except brain and RBCs
what protein is responsible for FA uptake into cells?
CD36
what happens to FAs after cellular uptake?
fatty acyl-CoA synthases catalyze fatty acyl-CoA.
fatty acyl-CoA synthase requirese ATP and pyrophosphatase
however, this cannot pass through the mitochondrial matrix, so it is converted via carnitine acyltransferase 1 (CAT-1) to fatty-acyl carnitine, which is permitted to pass
CAT-1
enzyme that converts fatty acyl-CoA into fatty-acyl carnitine for passage into mitochondria. allosterically inhibited via malonyl-CoA, which is in high [ ] when glucose is present
CAT-II
reforms fatty acyl-CoA from fatty acyl- carnitine
describe B-oxidation inside the mitochondria
oxidation occurs initially at the B carbon, and goes through cycles releasing 2 C acetyl-CoAs. Each cycle produces 1 FADH2 and 1 NADH. The acetyl-CoAs can then enter the TCA, but this requires anapleurotic rxns to form OAA
thus, there must always be SOME glucose oxidation in order for B-oxidation to occur, in order to replenish glucose via pyruvate carboxylase
describe the energy yield per mol of fatty acyl-CoA
80 ATP from acetyl CoAs
10.5 from FADH2
17.5 from NADH
ATP utilization -2
106 total per mol
describe ketogenesis
occurs only in the liver w/ low levels of oxaloacetate (d/t low levels of glucose), when the acetyl-CoA is shuttled into an alternative pathway
this forms acetoacetate and B-hydroxubuyrate- the ketone bodies
still requires mitochondria, oxygen, OAA, and succinyl-CoA
OAA requirement means need some glucose metabolism
where does ketone oxidation occur?
the BRAIN and muscle.
how are ketones taken up?
monocarboxylate transporter
how does the energy yield compare to glucose?
more energy yielded and less oxygen required
