Dietary Fats And Blood Lipids Lab Flashcards
What is the energy content per unit weight of fats?
Approx 9 kcal/g
What is the energy content per unit weight of proteins and carbohydrates?
Approx 4 kcal/g
In terms of the general population, what proportion of our energy should come from fats?
About a third:
- 70g per day for women
- 90g per day for men
List some of the molecules which are considered ‘fats’.
- sterols e.g. cholesterol
- phospholipids
- triglycerides
What is a fatty acid?
A carboxylic acid (COOH) with a long chain of hydrocarbons.
How many fatty acids does a triglyceride contain?
3
How many fatty acids does a phospholipid contain?
2
How many fatty acids does cholesterol contain?
1
How much saturated fat does the government recommend men and women consume each day?
Women < 20g
Men < 30g
What is a saturated fat?
A fat with no double bonds between carbon atoms.
What is an unsaturated fat?
A fat with 1 or more double bonds between carbon atoms (mono- or poly-).
What are the main types of polyunsaturated fats?
Omega-3 and omega-6
What are the 2 distinct structural configurations of unsaturated fatty acids?
Cis and trans
Describe cis-unsaturated fatty acids.
- hydrogen atoms attached to the carbon double bond on the same side
- have a bent configuration
Describe trans-fatty acids.
- hydrogen atoms attached to carbon double bonds on different sides
- generally linear in structure
- do not occur commonly in nature, usually produced by industrial hydrogenation
List some examples of foods high in saturated fat.
- pastry
- coconut oil
- hard cheese
- soured cream
List some examples of foods high in mono-unsaturated fat.
- avocado
- olives
- rapeseed oil
List some examples of foods with poly-unsaturated fat.
- salmon
- rapeseed oil
- walnuts
Why is fat essential for the body?
- provides energy, essential fatty acids and fat soluble vitamins (A, D, E, K)
When are fats referred to as lipids?
Once they are digested and absorbed in the bloodstream
Why are lipids transported in lipo-proteins?
Because they are insoluble in water and blood.
Describe the basic structure of a lipoprotein.
- complex spherical structure
- hydrophobic core
- hydrophilic coating
What is found in the hydrophobic core of lipoproteins?
Triglycerides and cholesterol esters
What is contained in the hydrophilic surface of lipoproteins?
Phospholipids, free cholesterol and apolipoproteins.
List the types of lipoproteins.
- chylomicrons
- very low density lipoproteins (VLDLs)
- low density lipoproteins (LDLs)
- high density lipoproteins (HDLs)
What is the function of a chylomicron?
- synthesised in the gut after a meal
- main carrier of dietary triglycerides from gut to adipose and muscle tissue
What is the function of a VLDL?
- synthesised in the liver
- main carrier of endogenously produced triglyceride to skeletal muscle
What is the function of an LDL?
- generated from VLDL in the circulation
- main carrier of cholesterol from liver (via VLDL) to tissues
What is the function of an HDL?
Protective - returns cholesterol from extrahepatic tissues to the liver for excretion
List the 4 main lipoproteins from least dense to most dense.
- Chylomicrons
- VLDLs
- LDLs
- HDLs
What are apolipoproteins?
The protein component of lipoproteins, amphipathic compounds with hydrophobic region interacting with lipid cord and hydrophilic region interacting with aqueous environment.
Why are apolipoproteins important?
- help maintain the strucutre of lipoproteins
- regulate the metabolism and uptake of lipids in to cells
- identifying the type of lipid in lipoprotein
What are the 3 major pathways of cholesterol metabolism?
Exogenous (intestinal), endogenous (hepatic) and the reverse cholesterol transport.
Describe the exogenous lipid cycle.
- Dietary cholesterol and fatty acids absorbed via the small intestine.
- These are incorporated into chylomicrons that are secreted via the lymphatics reaching the bloodsteam via the thoracic duct.
- In the circulation, chylomicrons decrease in size as triglycerides are removed by the enzyme lipoprotein lipase which is present in capillaries of adipose tissue and muscle.
- The deflated chylomicron remnants are taken up by the liver where the cholesterol is either utilised or secreted in bile.
Describe the endogenous lipid cycle.
- VLDL particles are synthesised in the liver.
- In the circulation, lipoprotein lipase hydrolyses VLDL to a form of IDL and then LDL.
- LDL may be removed from the circulation by high affinity LDL receptors into cells or by scavenger routes (when LDL levels are high) into macrophages leading to atheromatous plaques.
Describe the reverse cholesterol transport pathway.
- HDL particles act as cholesterol ester shuttles which help remove the sterol from peripheral tissues and return it to the liver, either directly or via other lipoproteins.
- This is thought to be anti-atherogenic, with an elevated HDL conferring a decreased risk of CHD.
What is the main apolipoprotein in chylomicrons?
B48
What is the main apolipoproteins in VLDL?
B100
What is the main apolipoprotein in LDLs?
B100
What is the main apolipoprotein in HDLs?
A1, A2
What do LDL receptors do?
Recognise LDL cholesterol and lead to uptake of LDL in to cells to then be degraded to cholesterol.
What happens if cholesterol concentration levels fall?
- LDL receptors are upregulated
- more cholesterol is taken up by the cell
- this leads to lower blood concentrations
Where is cholesterol absorbed in the GI tract?
Small intestine
Which enzyme hydrolyses VLDL to form IDL?
Lipoprotein lipase
How can LDL be removed from the circulation?
- by high affinity LDL receptors in to the cell
- by scavenger routes when LDL levels are high into macrophages leading to atheromatous plaques
What happens if the fatty acid chain in cholesterol in LDL molecules becomes oxidised?
- LDL particles are not taken up by normal LDL receptor on the liver
- they are taken up at a faster, uncontrolled rate and amount by scavenger receptors on macrophages
- this leads to formation of cholesterol laden foam cells which can develop in to fatty streaks and atheromatous plaques which cause narrowing of the arteries.
How can the end products triglyceride rich lipoproteins promote the deposition of cholesterol in artery walls?
By damaging the endothelial lining.
What is checked during a lipid profile?
- total cholesterol
- triglycerides
- HDL cholesterol
- LDL cholesterol
