BCM261: Theme 1: Lipid catabolism and
energy production
Chapter 17: Summary
- fats are an important energy source in animals
- two-carbon units in fatty acids are oxidized in a four-step b oxidation process into acetyl-CoA
- in the process, a lot of NADH and FADH2 forms; these can yield a lot of ATP in the electron-transport
chain
- during peroxisomal oxidation, fats can be oxidized to generate heat
- acetyl-CoA formed in the liver can be either oxidized via the citric acid cycle or converted to ketone
bodies that serve as fuels for other tissues
,Digestion, mobilization and transport of lipids
Oxidation of Fatty Acids Is a Major Energy Source in Many Organisms
- About one-third of our energy needs comes from dietary triacylglycerols.
- About 80% of energy needs of mammalian heart and liver are met by oxidation of fatty acids.
- Many hibernating animals, such as grizzly bears, rely almost exclusively on fats as their source of
energy
Fats Provide Efficient Fuel Storage
- The advantage of fats over polysaccharides:
o Fatty acids carry more energy per carbon because they are more reduced.
o Fatty acids complex or carry less water because they are nonpolar (store a lot
more fatty acids in a smaller space).
- Glucose and glycogen are for short-term energy needs and quick delivery.
- Fats are for long-term (months) energy needs, good storage, and slow delivery.
Fatty acid fuel sources
- Fats in diet
- Fats stored as lipid droplets in cells and adipose tissue
- Fats synthesized in one organ for export to another liver
- Fats obtained by autophagy (membranes of cells contain fats)
Dietary Fatty Acids Are Absorbed in the Vertebrate Small Intestine
,Step 1
- Bile salts (stored in gallbladder) amphipathic
molecules
- Synthesized from cholesterol
- Act as biological detergents
- Micelle increases fraction of lipids accessible to water
soluble lipases
Step 2
- Lipases release FAs from TAGs
- Phospholipases release FAs from phoshoacylglycerols
- Both hydrolyze the ester bond between the fatty acid and the rest of the molecule
- Phospholipases – Site-specific
Chylomicron Formation
- apolipoproteins = proteins in their lipid-free form that bind lipids to form lipoproteins
o target triacylglycerols, phospholipids, cholesterol, and cholesteryl esters for transport
between organs
- chylomicrons = particles consisting of triacylglycerols, cholesterol, and apolipoproteins
- FA transported in blood after packaging with proteins
- Major lipids in aggregates are cholesterol and its esters (hydroxy-group esterified to fatty acids), as
well as triacylglycerols
- Chylomicrons are involved in transport of dietary lipids, whereas the other lipoproteins deal mainly
with endogenous lipids
, NB Principle
Allosteric mechanisms and posttranslational regulation (protein phosphorylation) coordinate metabolic processes within a cell.
Hormones and growth factors coordinate metabolic activities among tissues and organs. Reciprocal regulation of catabolic and
anabolic pathways prevents the inefficiency of futile cycling (synthesising while breaking down the same molecule simultaneously).
Hormones Trigger Mobilization of Stored Triacylglycerols
glycerol-3- dihydroxyacetone glyceraldehyde-3- Glycolysis
glycerol
phosphate phosphate phosphate
energy production
Chapter 17: Summary
- fats are an important energy source in animals
- two-carbon units in fatty acids are oxidized in a four-step b oxidation process into acetyl-CoA
- in the process, a lot of NADH and FADH2 forms; these can yield a lot of ATP in the electron-transport
chain
- during peroxisomal oxidation, fats can be oxidized to generate heat
- acetyl-CoA formed in the liver can be either oxidized via the citric acid cycle or converted to ketone
bodies that serve as fuels for other tissues
,Digestion, mobilization and transport of lipids
Oxidation of Fatty Acids Is a Major Energy Source in Many Organisms
- About one-third of our energy needs comes from dietary triacylglycerols.
- About 80% of energy needs of mammalian heart and liver are met by oxidation of fatty acids.
- Many hibernating animals, such as grizzly bears, rely almost exclusively on fats as their source of
energy
Fats Provide Efficient Fuel Storage
- The advantage of fats over polysaccharides:
o Fatty acids carry more energy per carbon because they are more reduced.
o Fatty acids complex or carry less water because they are nonpolar (store a lot
more fatty acids in a smaller space).
- Glucose and glycogen are for short-term energy needs and quick delivery.
- Fats are for long-term (months) energy needs, good storage, and slow delivery.
Fatty acid fuel sources
- Fats in diet
- Fats stored as lipid droplets in cells and adipose tissue
- Fats synthesized in one organ for export to another liver
- Fats obtained by autophagy (membranes of cells contain fats)
Dietary Fatty Acids Are Absorbed in the Vertebrate Small Intestine
,Step 1
- Bile salts (stored in gallbladder) amphipathic
molecules
- Synthesized from cholesterol
- Act as biological detergents
- Micelle increases fraction of lipids accessible to water
soluble lipases
Step 2
- Lipases release FAs from TAGs
- Phospholipases release FAs from phoshoacylglycerols
- Both hydrolyze the ester bond between the fatty acid and the rest of the molecule
- Phospholipases – Site-specific
Chylomicron Formation
- apolipoproteins = proteins in their lipid-free form that bind lipids to form lipoproteins
o target triacylglycerols, phospholipids, cholesterol, and cholesteryl esters for transport
between organs
- chylomicrons = particles consisting of triacylglycerols, cholesterol, and apolipoproteins
- FA transported in blood after packaging with proteins
- Major lipids in aggregates are cholesterol and its esters (hydroxy-group esterified to fatty acids), as
well as triacylglycerols
- Chylomicrons are involved in transport of dietary lipids, whereas the other lipoproteins deal mainly
with endogenous lipids
, NB Principle
Allosteric mechanisms and posttranslational regulation (protein phosphorylation) coordinate metabolic processes within a cell.
Hormones and growth factors coordinate metabolic activities among tissues and organs. Reciprocal regulation of catabolic and
anabolic pathways prevents the inefficiency of futile cycling (synthesising while breaking down the same molecule simultaneously).
Hormones Trigger Mobilization of Stored Triacylglycerols
glycerol-3- dihydroxyacetone glyceraldehyde-3- Glycolysis
glycerol
phosphate phosphate phosphate
