Lecture 25: Fatty acids as fuel 1 Flashcards
Name two key dietary lipids obtained in our diet:
- phospholipids (membranes)
- sterols (including types of cholesterol)
Which of these lipids constitutes over 90% of our dietary fat?
- triacylglycerols (includes fatty acids) make up over 90% of lipids in food
Briefly describe the structure of fatty acid.
- Fatty acid: carbon chain attached to a carboxylic acid
What is triacylglycerol composed of?
- Glycerol (3C) with three fatty acids (acyl groups) attached
Lipids are made soluble for digestion by _______ acids which act as detergents. They are made from _____________, synthesized in the ________, stored in the ______ __________ and secreted into the ____________.
Lipids are made soluble for digestion by bile acids which act as detergents. They are made from cholesterol, synthesized in the liver, stored in the gall bladder and secreted into the small intestine (duodenum)
What is a micelle, and how is it structured?
Bile acids Form micelles:
- Bile acids: hydrophilic side facing out & hydrophobic facing in
- TAGs inside
- Provide surface area for digestion in an aqueous environment
What is the main enzyme system involved in lipid digestion?
pancreatic lipase performs the main digestion of TAGs in the small intestine
What is a lipoprotein and what is its function?
Function:
Provide a ‘delivery system’ for transporting lipids (in TAGs)
around the body
Help ‘solubilize’ lipids for transport in blood from digestion
and the liver around the body
How is a lipoprotein structured?
Basic structure:
- Phospholipids (membrane)
- Unesterified cholesterol (no fatty acids attached) (in membrane)
- Esterified cholesterol (fatty acid attached) (inside)
- TAGs
AND
Apoproteins:
- structural for assembly (Apo-B)
- ligands for cell surface receptors (Apo-E & Apo-B)
- enzyme cofactors (Apo-CII for lipoprotein lipase)
What are the four classes of lipoproteins, and how are they classed?
Chylomicrons
- Low protein:lipid (~1:50)
- TAG transport
Very low-density lipoprotein (VLDL)
- Medium protein:lipid (~1:9)
- TAG transport
Low-density lipoprotein (LDL)
- Cholesterol transport
High-density lipoprotein (HDL)
- Cholesterol regulation/ mopping up
What are the two major lipid transport pathways and which lipoprotein is used in each?
Exogenous Pathway:
Uses chylomicrons to transport dietary lipids. After delivering triglycerides, chylomicrons become chylomicron remnants, which are taken up by the liver.
Endogenous Pathway:
Uses VLDL to transport liver-synthesized lipids. After delivering triglycerides, VLDL becomes VLDL remnants and is further processed into LDL to deliver cholesterol to tissues.
What is the function of the lipoprotein lipase enzyme?
Enzyme found on the endothelial surface of capillaries
Hydrolyses TAG in lipoproteins to monoacylglycerol and fatty acids which enter tissues
Highest activities in heart and skeletal muscle and adipose tissue
Lipoprotein lipase is activated by ApoCII
Chylomicron remnant remains in blood
Fatty acids can be used as fuel or stored
What would a defect in ApoCII or Lipoprotein lipase lead to in the blood?
Defects (by mutation) in either ApoCII or lipoprotein lipase lead to elevated levels of chylomicrons and plasma triacylglycerol in the blood
Why does the body store fats rather than carbohydrates?
Fatty acids are more reduced than carbohydrates (more energy released when oxidized in pathways)
Stored carbohydrate (glycogen) is approximately 2/3 water
So why store as fat?
Fat takes up much less space when stored as it is very energy dense and has low levels of water compared to glycogen which takes up a lot more space in the body for the equivalent amount of energy
What muscle type uses fat as their preferred fuel type?
Red muscle (endurance tissue) uses fat as the preferred fuel source
