What are triacylglycerols? what is it made up of? What are two structural types? What is the role of triacylglycerols? What is its characteristic in the body? What is the major comparison between triacylglycerols and carbohydrate & proteins?
- fat/ lipids/ triglycerides
- 3 fatty acid chains and 1 glycerol backbone
- simple: 3 identical fatty acids; mixed: 2 or 3 different fatty acids
- major energy store and major dietary lipids in humans
- insoluble in water and stored in specialised adipose fat cells
- energy yield from the complete oxidation of fatty acids is about 39kJg-1 while 13kJg-1 for carbohydrates and protein
What is the process of breakdown of triacylglycerols (different parts)? How are dietary fats broken down in the intestine? What special about the digestion and uptake process?
- fatty acids are released from the glycerol backbone by the action of lipases
- free fatty acids can then be degraded by β-oxidation to produce energy
- glycerol backbone is converted into DHAP (dihydroxyacetone phosphate) which enters glycolysis
- In the intestine, dietary fats are hydrolysed by pancreatic lipase
- both the digestion and uptake processes are aided by the detergent-like properties of bile salts –> induce fat emulsification
What is the structure of fatty acids? What do they most like? What are the two types of fatty acids? What is the relationship between the length of hydrocarbon chain and the solubility?
- a long hydrocarbon chain as tail with a terminal carboxylic acid group as head
- most have an even number of carbon atoms in an unbranched chain
- saturated: no double bonds; mono-/poly-unsaturated: one or more double bonds
- the longer the length of hydrocarbon chain, the lower the solubility is
What are the functions of fatty acids?
- components of cell membranes (phospholipids)
- as energy store (triacylglycerol)
- derivatives can serve as hormone-like substances (eg. prostaglandins) and intracellular second messengers (eg. diacylglycerol)
Where does the breakdown of fatty acids take place? What is it known as and what does it do? How is the fatty acid broken down? What does one acetyl CoA produce?
- occurs in the mitochondrial matrix
- known as β-oxidation which oxidises long-chain fatty acids to produce ATP
- removal of acetyl CoA from the end of acyl chain of fatty acids
- each acetyl CoA generates 12 ATP (3NADH, 1 FADH2, 1 GTP) in citric acid cycle and oxidative phosphorylation
What is the energy yield for fatty acid breakdown?
- each round: 1 FADH2, 1 NADH and 1 acetyl CoA are produced
- β-oxidation of 1 fatty acid:
=> from FADH2 and NADH produced (3+2)x7 = 35 ATP
=> from acetyl CoA produced 12x8 = 96 ATP - 2 ATP equivalents are required to activate palmitate to acyl CoA
- net yield: 35 + 96 - 2 = 129 ATP
What are the roles of cholesterol? How can it be obtained?
- important constituent of cell membranes
- precursor of steroid hormones such as progesterone, testosterone and cortisol
precursor of bile salts - obtained from diet or synthesised by the liver
What are the two types of bile salts? What are bile salts? How is it formed and where does it store? What is the use of bile salts? What will the lipid happens after emulsification?
- glycocholate and taurocholate
- major excretory form of cholesterol
- formed from cholesterol in the liver and stored in the gall bladder
- breakdown lipids into lipid droplets to increase the surface area for digestion by lipases and absorption into intestinal cells
- hydrophobic tail dissolved inside the fat droplets and the hydrophilic head sticking out, as the hydrophilic head carries a negative charge, so it is very difficult for the droplets to fuse together again
What are the precursors of steroid hormones? What are the five classes of steroid hormones? What are their respective examples, site of synthesis and action?
- cholesterol
- progestogens; progesterone; corpus luteum; prepares uterine lining for egg implantation and maintenance of pregnancy
- androgens; testosterone; testis; development of male secondary sex characteristics
- estrogens; estrone; ovary; development of female secondary sex characteristics
- glucocorticoids; cortisol; adrenal cortex; promotes gluconeogenesis and glycogen formation and enhance protein and fat degradation
- mineralocorticoids; aldosterone; adrenal cortex; increases reabsorption of Na+ and excretion of K+ and H+ by kidney tubules
What is the general mechanism of steroid hormone action?
- steroid hormones cross the cell membrane and bind to a cytosolic or nuclear receptor
- receptor-hormone complexes bind to regulatory DNA sequences which stimulate or inhibit the expression of specific genes
Why are there lipoproteins? What are the 5 types and what are their functions respectively (according to their density; low to high)?
- triacylglycerols, cholesterols and phospholipids are insoluble in aqueous solution, so they are transported as lipoproteins
- chylomicron –> transport dietary lipids from the intestine to other tissues –> free fatty acids for tissue consumption and storage
- very low density lipoprotein (VLDL) –> carry endogenous lipids from the liver to tissue for storage
- intermediate density lipoprotein (IDL)
- low density lipoprotein (LDL) (bad) –> transport cholesterol from the liver to extrahepatic tissues –> transport process may lead to blockage of blood vessels
- high density lipoprotein (HDL) (good) –> transport cholesterol from tissues to the liver for degradation –> reverse cholesterol transport –> clears up cholesterol accumulated in various tissue and artery wall
What is the reason of development of atherosclerosis? What are the symptoms and risk factors of atherosclerosis? How to prevent it?
- high LDL –> deposit on artery walls –> macrophage treat deposit as foreign substances –> cholesterol plaque formed –> create stress to the blood vessels –> constant stretching –> when the force become too vigorous, the plaque may burst and bleed –> blood coagulation –> thrombosis –> blood flow will be completely stop –> stroke/ heart attack
- angina and chest pain
- smoking, family history, gender, high bp, diabetes and high LDL
- exercise, diet and medications
