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2012-02-14 22:29:07

Structure, function, metabolism
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  1. Give 2 examples of SFA, MUFA and PUFA.
    • SFA: butyric acid, palmitic acid
    • MUFA: oleic acid, elaidic acid
    • PUFA: linoleic acid, arachdonic acid
  2. What is the delta and omega system of FA nomenclature?
    • Delta: starts at the carboxyl end
    • Omega: starts from methyl end
  3. What are the two essential FA? Why are they essential?
    • Linoleic acid (omega 6) and Alpha linolenic (omega 3)
    • They are essential because human enzymes lack the ability to insert a double bond beyond the delta 9 position (at delta 12 and delta 15 positions) therefore aren't produced in the body
    • This enzyme is only found in plants
    • We receive these nFA from plants
  4. What are the signs of n-6 deficiency and n-3 deficiency?
    • n-6: dermatitis, decreas in growth and reproductive maturity - FA incorprates into cell membrane of skin cells
    • n-3: decrease in IQ (affects CNS development) and decreases visual acuity (affects retinal development) - FA associated with membranes in the brain
    • FA get incorporated into cell membranes
  5. What are the desaturation and elongation pathways for EFA (abbreviated)?
    • Repetitive series of desaturations and elongation by 2Cs coming from acetyl CoA
    • Linoleic acid (n-6) gets converted eventually to arachidonic acid which get converted to pro-inflammatory eicosanoids
    • Alpha linolenic acid (n-3) gets converted to eicosapentanoic acid (EPA) and docosahexanoic acid (DHA)
    • EPA is a precursor for anti-inflammatory eicosanoids
    • DHA is involved in the development of brain cell membranes - related to CNS and retinal development
    • Usually have more n-6 FA
  6. What is the difference between pro and anti inflammatory eicosanoids?
    • Pro: important physiological response to fighting infections and mounting inflammation - thermal biological response
    • Anti: dampen inflammation response in the body - important in arthritis
  7. What is an eicosanoid?
    • 20 carbon metabolite of AA and EPA
    • Produced by most cells in the body
    • Hormone like, local function
    • Role in inflammation, platelet aggregation and blood pressure
    • Implcations for disease
    • Pro inflamm causes too much aggregation
    • After FA are incorporated into cell membranes, the cell will convert them eicosanoids
  8. How are TAGS used?
    • Main dietary form and major storage form
    • used in lipolysis and lipogenesis (in adipose tissues)
    • Can have MAG, DAG, TAG
  9. What are the main functions of phospholipids?
    • Main compoenents if cell membranes - lipid bilayers
    • Source of physiological active compounds (eicosanoids)
    • Anchors membrane proteins
    • Intracellular signalling
  10. What is the role of phosphotidyl choline?
    Found in diet and plays a role as an emulsifier
  11. What are the sources and principal functions of sterols? What are the structural features?
    • 40% diet and 60% endogenous production
    • Components of membranes
    • Bile acids
    • Steriod sex hormones
    • Vitamin D
    • Also has teriod nucleus - 4 ring structure - animal cholesterol is seen as bad and plant cholesterols as good
    • The liver produces sufficient cholesterol for body
  12. What are the 7 lipid functions?
    • 1.Concentrated source of energy
    • 2. Palatability and satiety
    • 3. Source of FA
    • 4. Carrier of fat soluble vitamins (A, D, E, K)
    • 5. Involved in hormone production
    • 6. Affect blood clotting and inflamation
    • 7. Associated with disease development: obesity, diabetes, heart disease
  13. At what organs does lipid digestion occur and how?
    • Mouth: secretes lipases
    • Stomach: gastric lipases
    • Liver: production of bile salts and salts which allows alipids to come into contact with enzymes in the rest of digestion
    • Gallbladder: stores the bile - source - bile allows for emulsification
    • Small inestine: pancreatic lipases - main site of lipid digestionand cholesterol estrase - breaks down cholesterol as most in the form of a cholesterol ester
  14. How are digested lipids stabilized? What are mixed micelles?
    • Stabilized by bile salts = conjugate of bile acids
    • Small, spherical complexes containing lipid digested products and bile salts
    • Can access intramicrovillus spaces of the membrane
    • originally thought the lipids were delivered into intestinal mucosal cell through passive diffusion, but carrier mediated transporters have been identified
    • Bile salts are reabosrbed
  15. Describe the structure of a micelle?
    • Have amphipathic phospholipids and bile salts on outside surrounding and stabilizing the structure
    • FA, MAG, lysolecithin and cholesterol inside
  16. What happens once lipids are absorbed into the intestinal mucosal cell?
    • Enters the cell as a micelle
    • They are resynthesized into cholesterol esters, TAGs and phosphotidyl choline and packaged into a chylomicron and enters lymphatic system
    • Short chain FA can pass directly through the membrane but then attach to albumin which then transports it through portal circulation
  17. What is a chylomicron?
    • It is a lipoprotein
    • Synthesized directly in intestinal mucosal cell
    • Phsopholipids play structural role on outside
    • Have apoproteins either on inside of membrane or outside - allow stabilization within the blood circulationand provide recognition functions
  18. What is the affect on chylomicrons after a meal?
    • The amount of chylomicrons increases
    • Clearance is due to lipoprotein lipases (LPL)
    • Found on endothelial cell surface of small blood vessels and capilleries
    • LPL in adipose and muscle tissue NOT liver
    • LPL releases a FA and DAG from a TAG which can then be absorbed by the body
    • Chylomicron remnants are removed from the blood at the liver
  19. What happens when the chylomicron remnant reaches the liver?
    • The contents along with lipids from other sources get repackaged into VLDL which forms LDL
    • Some HDL is produced as well
    • The chylomicron remnants are resynthsized to larger structure to form a FA pool leading to a TAG pool which are then repackaged into VLDL and taken up by the hepatic cells into circulation
  20. What lipid metabolism occurs in the adipose tissues?
    • After eating...
    • Contents of VLDL, LDL and HDL are broken down by LPL, taken up by adipose tissues and resythnesized as TAG and stored in TAG pool - can be used for energy later on
  21. What is LDL? It's main function?
    • VLDL is the main transporter of newly syntheized TAGs from the liver
    • LDL delivers cholesterol in essential places but if no more requirements for cholesterol, will begin to deposit it anywhere - seen as bad
  22. What is the function of HDL?
    • Produced in liver and involved in reverse choelsterol transport - picks up remnants of cholesterol and brings it back to the liver to be used in bile acids or excreted
    • Lecithin cholesterol acetyl transferase converts it to cholesterol esters - form of transportation
  23. What is the effect of lowering dietary cholesterol?
    • In most cases, this has little effect on cholesterol levels as most if produced by your body
    • Exception is the dietary gene interaction in which there is a polymorphism that causes lowering dietary cholesterol to effectively lower blood level cholesterols (10-25% of people)
  24. Where do trans FA occur?
    • naturally in ruminant fat (4-8% of ruminant milk are trans FA) - most common is elaidic acid
    • Also made through partial dehdrogenation processes which convert cis FA to trans form
    • This is done to increase stability and shelf life
  25. What are the health risks associated with trans FA?
    Double negative - increases LDL and decreases HDL which is linked to cardiovascular disease