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| Question | Answer |
| What is cholesterol a precursor for? | 1. Bile acids/salts 2. Vit D 3. Steroid hormones |
| What are the components of bile? | Bile acids, phospholipids, cholesterol, bilirubin |
| Where are bile acids stored? | In bile in gall bladder |
| Where are bile acids formed? | Liver |
| Name the two most important bile acids and their precursors | 1. Taurocholate: taurine + cholesterol; 2. Glychocholate: glycine + cholesterol |
| Why are bile salts referred to as detergents? | Contain both hydrophobic (cholesterol) and hydrophilic parts (polar groups) |
| What is liver cholestasis? | Toxicity of liver due to high levels of bile salts |
| What % of bile acids are reuptaken from the intestines into the liver, where does the rest go? | 98% reuptake 2% lost in faeces |
| How is cholesterol lost from body? | In faeces: 0.5g in bile acids, 0.5g as free cholesterol per day |
| What are gall stones? | Cholesterol-rich stones in gall bladder due to excess cholesterol crystallising in bile |
| Where is the main site of steroid hormone synthesis? | Adrenal cortex in kidney |
| What enzyme is used in the formation of steroid hormones from cholesterol? | Desmolase: forms progestagens |
| Name three categories of steroid hormones formed in the adrenal cortex | 1. Glucocorticoids 2. Mineralocorticoids 3. Androgens |
| What is required for formation of vit D from cholesterol and how does it work? | UV light Breaks hydrocarbon ring in cholesterol to form a more open structure. This forms pre. vit D which spontaneously isomerises to vit D |
| How are lipids transported around the body? | In lipoproteins |
| What are lipoproteins composed of? | Lipid (cholesterol or TG) and apoprotein |
| What is found in the core of a lipoprotein? | Dense esterified cholesterol and TG |
| Where is unesterified cholesterol found in lipoproteins? | Within phospholipid layer around periphery of the structure |
| What is the largest, least dense lipoprotein? | Chylomicron |
| List in order of density (high to low) the following: IDL, LDL, VLDL, HDL | HDL, LDL, IDL, VLDL |
| What is the general function of chylomicrons and chylomicron remnants? | Transport dietary lipids |
| Why is B100 apoprotein specifically important? | It is required for LDL to bind to specific cellular receptors |
| What is the function of HDL? | Reverse cholesterol transport, transports cholesterol from tissues to liver |
| What is the main cholesterol carrying lipoprotein? | LDL |
| Name the components of a chylomicron | Dietary TGs, apoB48, cholesterol (apoC-II, apoE) |
| What apoprotein activates lipoprotein lipase? | apoC-II |
| Where does the apoC-II and apoE on chylomicrons come from? | Donated from HDL |
| What effect does LPL have on chylomicrons? What is the resulting structure called? | Breaks down TGs to form FFAs and glycerol. Chylomicron remnants are formed , ApoC-II is recycled back to HDL |
| Where does the FFAs go from TG breakdown in chylomicrons? | Adipose tissue (storage), muscles (ATP production) |
| What happens to chylomicron remnants? | Deliver dietary cholesterol and some dietary TGs to liver due to apoE receptors in liver. |
| What are endogenous lipids? | Lipids in liver due to excess carbohydrates, lipids and cholesterol (synthesis or excess). |
| What do VLDLs contain? Where are they packaged? | Endogenous lipids in eluding TGs, cholesterol, phospholipid, also apoB-100. Packaged in liver |
| What enzyme breaks VLDL into IDL and how? | Lipoprotein lipase (LPL), apoC-II activates LPL that releases TGs from VLDL and breaks them down into FFAs and glycerol. |
| Where does the FFAs go from the break down of VLDL by LPL? | Adipose or muscle |
| What two apoproteins are donated from HDL to both chylomicrons and VLDL? | ApoC-II, apoE |
| What two fates can IDL have? | 60% is destroyed in liver 40% become LDL by loss of further TGs |
| What is the desirable level of LDL in plasma? | <4.1 mol/L |
| What three places does cellular uptake of LDL occur? | Liver, peripheral tissues, macrophages |
| Cellular uptake of LDL requires which apoprotein? What is the process of uptake called? | ApoB-100 as it is recognised by specific receptors on the cell surface. Receptor mediated endocytosis |
| What two mechanisms do statins use to reduce cholesterol? | 1. Inhibit HMGCoA reductase in the biosynthesis pathway of cholesterol 2. Cause upregulation of LDL by LDL receptors = reduce plasma levels |
| Name the three types of HDLs and their shapes | 1. Pre-beta HDL: disc shaped 2. HDL3: spherical 3. HDL2 spherical |
| Pre-beta HDL acquires cholesterol and forms what? | HDL3 |
| Cholesterol in HDL3 has undergone what process and by what enzyme? | Esterification (esterified cholesterol) by LCAT |
| What apoprotein activates LCAT? | ApoA-1 |
| What is the action of CETP? | Cholesterol ester transfer protein Allows HDL3 to exchange esterified cholesterol for TGs from VLDLs and other lipoproteins. This increases the size of the HDL3 forming HDL2 that contains CE and TGs. |
| What is the fate of HDL2? | Transported to liver where apoA-1 activates liver cells for uptake of CE and TGs. |
| Does anabolic or catabolic pathways dominate in the fed state? | Anabolic |
| In the fed state describe the protein synthesis/breakdown cycle? | The rate of protein synthesis is balanced by the rate of protein degradation. No increase in muscle mass during the fed state. |
| Does insulin promote the synthesis or degradation of proteins in the protein balance cycle? | Protein synthesis |
| What three hormones are increased in the catabolic phase? | Glucagon, adrenaline, cortisol |
| Increase in the synthesis of what occurs in anabolism phase? | Glucagon, TGs, protein, other lipids |
| Breakdown of what occurs in the catabolism phase? | glucose, AAs, FAs, from tissue stores |
| Where is insulin synthesised? | Islets of Langerhans in beta cells of pancreas. |
| What is the half-life of insulin in the plasma? | 6 mins |
| What regulates insulin secretion? | 1. High plasma glucose 2. Amino acids from diet 3. Gastro-intestinal hormones (signalling molecule) |
| What regulates glucagon synthesis? | 1. Low glucose 2. Amino acids (endogenous) 3. Arenaline |
| What is insulin effect on AAs? | Increase uptake of AAs into cells, promoting protein synthesis |
| What is glucagon's effect on AAs? | Increases AA uptake in liver, C skeleton can be used for gluconeogenesis |
| What enters the pentose-P pathway in the liver? During what state? What does it form? | G6P Fed state NADPH |
| High acetyl CoA in the liver during the fed state can be converted/used in what? | 1. TCA cycle 2. Fatty acid synthesis |
| What are TGs packaged into in the liver during the fed state? | VLDL |
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