13 Questions
What is the main reason for the hydrophobicity of lipids?
The long -hydrocarbon chains
In infants, what catalyzes the digestion of dietary lipids in the stomach?
Both A and B
What is the main component of dietary lipids?
Triacylglycerol
What is the role of pancreatic lipase in the digestion of dietary lipids?
Hydrolyses triacylglycerols to 2-monoacyl glycerol and 2 free fatty acids
Why is the rate of hydrolysis slow in the stomach?
Because the lipid is not yet emulsified
What is the function of phospholipase A2 in the digestion of dietary lipids?
Removes a fatty acid at carbon 2 of a phospholipid
How are lipids absorbed by intestinal mucosal cells?
By micelles formation
In adults, where do dietary lipids progress to after passing through the stomach?
The small intestine
What is the primary function of mixed micelles in the intestinal lumen?
To solubilize amphipathic lipids in the aqueous environment
What is the fate of free fatty acids in the body?
They are transported in blood in association with serum albumin and then oxidized for energy
What is the primary destination of glycerol in the body?
The liver or kidney, where it is converted to glycerol-3-phosphate
Which of the following fatty acids does not require the assistance of a micelle for absorption?
Short and medium chain-length fatty acids
What is the primary outcome of fatty acid oxidation in cells?
The production of ATP through energy metabolism
Study Notes
Lipids
- Lipids are a heterogeneous group of water-insoluble (hydrophobic) organic molecules due to their long hydrocarbon chains.
- Hydrophobicity causes lipids to be insoluble in aqueous solutions, leading to compartmentalization in membranes or as droplets of fat in adipose tissue, or transportation in plasma as lipoprotein particles.
Digestion of Dietary Lipids
- Dietary lipids consist of 90% triacylglycerol (TAG) and 10% cholesterol and phospholipids.
- In infants, digestion begins in the stomach with acid-stable lingual lipase and gastric lipase, targeting TAG molecules with short or medium chain fatty acids.
- In adults, dietary lipids are not digested in the mouth or stomach, but rather progress intact to the small intestine.
Pancreatic Enzymes
- Pancreatic lipase hydrolyzes triacylglycerols to 2-monoacyl glycerol and 2 free fatty acids.
- Phospholipase A2 removes a fatty acid at carbon 2 of a phospholipid, leaving a lysophospholipid.
- Cholesterol esterase converts cholesteryl-esters to cholesterol and a free fatty acid.
Absorption of Lipids
- Lipids are absorbed by intestinal mucosal cells through micelles formation, with bile salts, free fatty acids, free cholesterol, and 2-monoacylglycerol forming clusters of amphipathic lipids.
- Short and medium chain-length fatty acids do not require micelles for absorption.
Fate of Lipids
- Free-fatty acids can directly enter adjacent muscle cells or adipocytes, or be transported in blood with serum albumin.
- Most cells can oxidize fatty acids to obtain energy (ATP).
- Glycerol is used by the liver or kidney to produce glycerol-3-phosphate, which can enter glycolysis or gluconeogenesis by oxidation to dihydroxyacetone phosphate.
Learn about the characteristics and properties of lipids, including their hydrophobicity, compartmentalization, and transportation in the body.
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