Fatty Acids as a Fuel Molecule - #1 Flashcards
describe lipids in the diet
lipids are hydrophobic or amphiphilic organic molecules
Includes:
- phospholipids (membranes)
- sterols (including types of cholesterol)
- triacylglycerols (includes fatty acids)
- over 90% of lipids in food
describe the structure and role of cholesterol in the body
Range of roles in the bode eg. membranes, signalling (hormones), bile salts
Can be made by the body
In diet as cholesterol esters (fatty acid attached)
Cholesterol structure: Hydrophobic ring structure (with side chain on one end and hydroxyl group on the other)
Cholesterol ester structure: same as cholesterol but instead of hydroxyl group, it has a long acyl chain attached to it
describe the structure and traits of fatty acids
- fatty acid: carbon chain attached to a carboxylic acid
- free fatty acids (FFA): not bound to another molecule
- lots of types but in BIOC we will focus on those with even number of carbons and no double bonds (saturated)
- carbon chain is hydrophobic: body has lots of aqueous environments so special mechanisms are required for transport
- amphiphilic molecule because big hydrophobic bit and then a little hydrophilic on the other end
describe the structure of triacylglycerol (TAG)
- mots fats in diet in form of triacylglycerols (TAGs; triglyceride)
- Glycerol (3C) with three fatty acids (acyl groups) attached
describe the digestion of TAGs
- lipases: enzymes that hydrolyses TAGs to release free fatty acids (FFA)
- range of lipases in different places in the body
- pancreatic lipase in small intestine hydrolyses fatty acids at positions 1 and 3 giving 2 FFA molecules and monoacylglycerol
(but fatty acids are non-polar, so how does the lipase get access?)
describe the structure and functions of bile acids (bile salts)
- bile acids are synthesised from cholesterol in liver
- ring structure of cholesterol (hydrophobic) with hydroxyl groups and/or carboxyl groups (hydrophilic) added
- stored in gall bladder as bile, then secreted into small intestine
bile acids solubilise fat for digestion
From micelles:
- bile acids: hydrophilic side facing out and hydrophobic side facing in
- TAGs inside
- provide surface area for digestion in an aqueous environment
- pancreatic lipase can fit in-between the bile salts that form the micelle and do their function from between these bile salts
- TAGS make small micelles that can then be absorbed by the epithelial cells
describe the function and structure or lipoproteins
- provide a ‘delivery system’ for transporting lipids (in TAGs) around the body
- help ‘solubilise’ lipids for transport in blood fro digestion and the liver around the body
Basic structure:
- single layer of phospholipids to make membrane that is a sphere structure
- unesterified cholesterol (no fatty acids attached) - in the membrane
- esterified cholesterol (fatty acid attached) - inside the lipoprotein
- TAGS - inside the lipoprotein
- Apoproteins: - in membrane
- structural for assembly
- ligands for cell surface receptors
- enzyme cofactors
what are the classes of lipoprotein and what do they transport?
there are different classes of lipoproteins that cary in amount (ratio of protein to lipid) and type of apoprotein
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
describe the role of LPL (lipoprotein lipase)
- lipoprotein lipase is an enzyme found on the endothelial cells 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 is activated by ApoCll
- chylomicron remnant remains in blood
- fatty acids can be used as fuel or stored
- defects (by mutation) in either ApoCll or lipoprotein lipase lead to elevated levels of chylomicrons and plasma treaclyglycerol
describe fatty acids as a fuel molecule
fatty acids are the preferred fuel for most tissues
red muscle cells tend to use fat (white muscle tend to use glucose) - for endurance
describe fatty acids as a storage molecule
fats is the primary energy store in mammals (5-25% body weight)
- adipose tissue
- TAGs
Why store fuel as fat?
- fatty acids are more reduced than carbohydrates (more energy released when oxidised in pathways)
- stored carbohydrate (glycogen) is approximately 2/3 water because it is polar so needs water surrounding it
- fatty acids are non polar so when stored take up less space
Excess energy consumed as glucose is stored as fat
- which is why low fat foods aren’t necessarily good because they have lots off extra sugar in them that get stored as fat anyway
describe the endogenous part of the fatty acid digestion, absorbtion and transport
Liver central role:
- recycles remnants (receptors)
- makes:
i) VLDL (with TAGs), released into blood
- LPL releases fatty acids for uptake into tissues
- then VLDL remnant is formed and this is recycled by the liver but also goes to for LDL which has a role in cholesterol to make bile salts too
ii) bile salts and cholesterol
Cholesterol transport (LDL)
- hepatic lipas to form LDL (cholesterol transport)
describe the exogenous part of the fatty acid digestion, absorption and transport
Dietary lipids
- TAGs broken down into MAG and 3 FFA
Absorption of small micelles TAGs made
TAGs packaged into chylomicrons in epithelial cells
Chylomicrons enter blood (via the lymph system)
Lipoprotein lipase (LPL)
Stored in muscle and adipose tissue
