Fatty Acid Catabolism Flashcards
cells can obtain fatty acid fuels from four sources:
- fats consumed in the diet fats
- stored in cells as lipid droplets
- fats synthesized in one organ for export to another
- fats obtained by autophagy
Dietary Fats Are Absorbed in the Small Intestine
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apolipoproteins
targets:
proteins in their lipid-free form that bind lipids to form lipoproteins
target triacylglycerols, phospholipids, cholesterol, and cholesteryl esters for transport between organs
chylomicrons
particles consisting of triacylglycerols, cholesterol, and apolipoproteins
Storage of Excess Fatty Acids
- fatty acids are converted to triacylglycerols in the liver
- triacylglycerols are packaged with specific apolipoproteins into VLDLs
- VLDLs are secreted and transported in the blood to adipose tissue
- triacylglycerols are removed and stored in lipid droplets within adipocytes in the adipose tissue
Hormones trigger mobilization of
stored triacylglycerols
lipid droplets
organelles stored in adipocytes and steroid-synthesizing cells that contain neutral lipids
contain a core of triacylglycerols and sterol esters surrounded by a monolayer of phospholipids
perilipins
family of proteins that coats the surface of lipid droplets to restrict access to the content of lipid droplets
prevent untimely lipid mobilization
Mobilization of Triacylglycerols Stored in Adipose Tissue occurs when -
What triggers changes that open the lipd droplet to the action of three cytosolic lipases?
- mobilization occurs when hormones (glucagon and epinepherine) signal the need for metabolic energy
- PKA triggers changes that open the lipid droplet to the action of three cytosolic lipases
free fatty acids, FFAs
fatty acids released by lipases
serum albumin
blood protein that noncovalently binds and transports FFAs to target tissues
makes up ~½ of the total serum protein
most of the biologically available energy of triacylglycerols resides in
their three long-chain fatty acids
phosphorylates glycerol to form glycerol 3-phosphate in the entry of glycerol into the glycolytic pathway
glycerol kinase
glyceraldehyde 3-phospbate can enter
glycolysis
Fatty acids are activated and transported into
mitochondria
small (< _____ carbons) fatty acids diffuse freely across mitochondrial membranes
<12 carbons
Transports long-chain fatty acids (containing 14+ carbons) through the mitochondrial membrane
carnitine shuttle
- requires activation to a fatty acyl-CoA and
- attachment to carnitine
fatty acyl-CoA synthetase
isozymes present in the outer mitochondrial membrane that activate the fatty acid by conversion to fatty acyl-CoA thioesters
fatty acid + CoA + ATP ⇄
fatty acyl-CoA + AMP + PPi
compound that transports fatty acyl-CoAs destined for mitochondrial oxidation across the inner mitochondrial membrane
carnitine
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acyl-carnitine/carnitine cotransporter
- allows the passive transport of the fatty acyl-carnitine ester
- moves one carnitine into the intermembrane space as one fatty acyl-carnitine moves into the matrix
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_____ pools of coenzyme A located ______
2; cytosol and mitochondria
coenzyme A in the mitochondrial matrix is largely used in:
oxidative degradation of pyruvate, fatty acids, and some amino acids
coenzyme A in the cytosol is used in the biosynthesis of
fatty acids
electron carrier that accepts electrons from FADH2
electron transfer flavoprotein (ETF)
flavoprotein that accepts electrons from ETF
ETF:ubiquinone oxidoreductase
passes electrons through ubiquinone into the mitochondrial respiratory chain
a multienzyme complex associated with the inner mitochondrial membrane that catalyzes steps 2-4 of the β-oxidation pathway for fatty acyl chains of 12+ carbons
allows efficient substrate channeling
trifunctional protein (TFP)
TFP is a ________ of alph4beta4 subunits
heterooctamer
α subunits contain enoyl-CoA hydratase and β-hydroxyacyl-CoA dehydrogenase activity
severe acidification of the blood and urine resulting from accumulated propionyl-CoA in the mitochondria being released to the blood as propionate
uses the carnitine shuttle
propionic acidemia
occurs in ~ 1 in 100,000 babies
the first intermediate of cytosolic fatty acid synthesis
blocks entry of fatty acids into mitochondria to prevent fultile cycling
malonyl-CoA
Oxidation of a Polyunsaturated Fatty Acid requires:
enoyl-CoA isomerase and 2,4-dienoyl-CoA reductase
β oxidation in peroxisomes has four steps:
peroxisomes = organelles found in plants and animals
- dehydrogenation
- addition of water to the resulting double bond
- oxidation of the β-hydroxyacyl-CoA to a ketone
- thiolytic cleavage by coenzyme A
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characterized by an inability to make peroxisomes
individuals lack all metabolism related to peroxisomes
Zellwger syndrome
characterized by the inability of peroxisomes to oxidize very-long-chain fatty acids
due to the lack of a functional transporter in the peroxisomal membrane
X-linked adrenoleukodystrophy (XALD)
a long-chain fatty acid with methyl branches that is derived from the phytol side chain of chlorophyll
the methyl group on the β carbon makes β oxidation impossible
phytanic acid
refsum disease
results from a genetic defect in phytanoyl-CoA hydroxylase