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Give 2 examples of SFA, MUFA and PUFA.
- SFA: butyric acid, palmitic acid
- MUFA: oleic acid, elaidic acid
- PUFA: linoleic acid, arachdonic acid
What is the delta and omega system of FA nomenclature?
- Delta: starts at the carboxyl end
- Omega: starts from methyl end
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
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
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
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
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
How are TAGS used?
- Main dietary form and major storage form
- used in lipolysis and lipogenesis (in adipose tissues)
- Can have MAG, DAG, TAG
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
What is the role of phosphotidyl choline?
Found in diet and plays a role as an emulsifier
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
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
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
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
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
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
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
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
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
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
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
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
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)
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
What are the health risks associated with trans FA?
Double negative - increases LDL and decreases HDL which is linked to cardiovascular disease