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31 Cards in this Set
- Front
- Back
Which form of carbs is the natural form? |
D |
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What are the sources of carbs? |
60% plant storage - starch small amounts of glycogen - <1% from animal muscle and liver about 25% in western diets comes from sucrose |
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Glycogen and starch comparison |
Glycogen - storage in mammals - highly branched Starch - storage in plants - 2 forms amylose and amylopectin - amylose is straight and forms coils - amylopectin is more branched |
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Amylose and cellulose comparison |
Amylose - Poly 1,4- alpha D glucopyranoside - broken down in mouth and intestine - glucose generated (also maltose) Cellulose - poly 1,4- beta D glucopyranoside (beta bond if the only difference) - principle component in dietary fibre - limited digestion in lower intestines, only possible due to bacterial enzymes |
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What is the difference between alpha and beta linkages? |
Alpha = away so the 6th carbon and the OH group on the first carbon point in opposite directions Beta = they point in the same direction |
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Uses of mono and disaccharides |
- energy - glycosylation of proteins (proteoglycans and glycoproteins) - structural components (GAGs, glycolipids) - carbon skeletons for biosynthesis of amino acid |
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Lipids - biological role (uses) |
Membranes - phospholipids energy reserves - TAGs Vitamins and hormones (steroids) Lipophillic bile Protection of organisms |
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FAs state at physiological pH |
FAs are readlily ionised at physiological pH and therefore give negative charge to molecules and fluids. |
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Lipid digestion |
Stomach - lingual lipaseand gastric lipase attack TAGs and hydrolyse small amount of FAs Small intestine - acid chyme (stomach contents) stimulates mucosa cells to release hormone which stimulates the pancreas and gall bladder to release digestive enzymes and bile respectively. Other mucosal cells release secretin which causes the pancreas to release bicarbonate rich fluid to neutralise the chyme. |
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Reactions of lipid digestion |
TAG - pancreatic lipase 2 FAs + Mono acylglycerol Cholesteryl ester - cholesteryl ester hydrolase Cholesterol + FA Phospholipids - Phospholipase A2 lysophospholipid + FA - lysophospholipase Glycerol Phosphoryl Lipase +FA |
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Lipid absorption |
Enzymic digestion creates polar products that form micelles of FAs, monoacylglycerol and cholesterol. These are absorbed. |
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Lipid transportation in circulation |
Lipids are insoluble in plasma. In order to be transported they form balls called chylomicrons with specific proteins (apoproteins). Chylomicrons have the hydrophilic areas on the outside and contain hydrophobic proteins and lipids on the inside (TAGs and cholesterol). |
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Function of apoproteins |
Other than forming chylomicrons apoproteins also have: - structural role - binding site for receptors - activators and co-enzymes for enzymes involved in lipid metabolism |
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Classes of lipoproteins |
Chylomicron - transport of dietary TAGs Very low density lipoprotein - transport of biosynthesised TAGs Low density lipoproteins -Delivers cholesterol to peripheral tissue High density lipoproteins - removes used cholesterol and returns it to the liver |
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What are chylomicrons? |
Assembled in intestinal mucosal cells Enter lymphatic system and then blood Contain mostly TAG but pick up apoproteins from HDL in circulation Function is to transport dietary TAG to adipose or muscle for storage or energy |
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Breakdown of chylomicrons |
Chylomicron circulates until they associates with lipoprotein lipase (enzyme on surface of cell). This is mediated by apoprotein C2 which is picked up from HDL in circulation. Lipoprotein lipase hydrolyses the TAG and the FAs diffuse into the local tissues. With the TAG gone the chylomicron shrinks and forms a chylomicron remnant. It dissociates from the lipoprotein protease and returns the C2 to the HDL. The remnant is taken up by the liver. |
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What are VLDLs? |
Synthesised in the liver. Contains mostly TAG but also a significant amount of cholesterol and cholesterol ester. Function is to transport endogenously synthesised TAG to extra hepatic (liver) tissue where it can be stored as fat or to muscle for energy. The cholesterol is delivered to extrahepatic tissues once the VLDL has been metabolised to LDL. Metabolism is essentially the same as chylomicrons |
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What are LDLs? |
Formed by metabolism of VLDLs Transports cholesterol to peripheral tissue |
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Role of LDL in atherosclerosis |
Endothelium is damaged LDLs penetrate vascular wall, deposit in the wall and are damaged by oxidation. Oxidised LDLs attract macrophages which ingest LDL. Macrophages become overloaded with lipid and become "foam" cells which die and release lipid in the vessel wall (forming plaques). Plaque matures to atherosclerotic plaque. Grows and constricts vessel. ETC ETC |
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What are HDLs? |
Act as a reservoir for apoproteins which can be donated or received by other lipoproteins Also play a vital role in scavenging "used" cholesterol HDLs are taken up by the liver and degraded, the cholesterol is secreted as bile salts or repackaged in VLDLs for redistribution. |
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What are bile salts? |
Excess cholesterol in liver is convert to bile salts. They are the polar constitute of the major excretory pathway of cholesterol. They are stored in the gall bladder and secreted into the small intestine to emulsify lipids. Almost all is reabsorbed and transported back to the liver. 1-2g is lost each day. Fibre can bind to bile salts and prevent i's reabsorption, this is one of the health benefits of fibre. |
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Where does carb digestion take place? |
Oral cavity - mechanical - chemical - salivary amylase (from the serous glands) Digestion in GI tract - chemical - enzymatic |
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Features of salivary amylase |
Optimal pH6.7 Active in oral cavity and in stomach for about 2 hours (until pH drops too far) Hydrolyses alpha 1,4 linkages of starch to oligosaccharides |
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Features of pancreatic amylase |
Secreted from exocrine acini into duodenum Optimal pH 6.7-7 Hydrolysis of 1,4 alpha bonds Responsible for digestion of more complex carbohydrate that take longer to breakdown to di or oligosaccharides |
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What are brush border enzymes? |
Enzymes found on surface of villi Maltase, sucrase, lactase optimal pH 7-8 Hydrolyse disaccharides to monosaccharides |
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Carbohydrate absorption |
Occurs in the small intestine (mainly the middle section) Villi and micro villi increase surface area to facilitate absorption Glucose and galactose enter the epithelial cells of the intestine via active transport using sodium dependent co-transport (it is the sodium potassium pump that requires energy) Glucose and galactose move into the blood stream via facilitated diffusion through GLUT2. |
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How is fructose absorbed? |
Facilitated diffusion in and out of epithelium GLUT5 and GLUT2 |
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Factors affecting carb absorption |
State of mucosa - faster through intact mucosa Thyroid hormones - increase absorption Mineralocorticoid increases rate of absorption Sodium concentration - increase absorption |
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Where are insulin and glucagon secreted from? |
Insulin - beta cells of Islets of Langerhans Glucagon - alpha cells |
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Structure and synthesis of insulin (needs checking) |
Small protein 2 polypeptide chains (A and B) linked by disulphide bond Synthesis: Proproinsulin ---RER----> Proinsulin ---TGN---> Insulin Stored as an inactive hexamer (monomer in active form) |
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Effects of diabetes |
Intracellular - glucogenesis and gluconeogenesis - breakdown of fats - ketone body production - diabetic ketoacidosis - decrease protein synthesis = body wastage, lethargy, increased appetite - susceptibility to infection, impaired wound healing Extracellular - changes to osmotic gradient = dehydration of cells = hyperglycaemic coma - blood glucose higher than renal threshold = urine has high sugar - increased urination - increased thirst |