Lipids part 1 Flashcards
What are lipids?
Heterogeneous organic molecules
Insoluble in water (hydrophobic), soluble in organic solvents
Exist in cell membranes, as lipid droplets in adipocytes (adipose tissue), in blood lipoproteins
What are the functions of lipids?
Stored form of energy
Structural element of membranes
Enzyme cofactors
Steroid Hormones
Vitamins A,D,E,K
Signalling molecules
What are the classes of lipids?
Fatty acids (1 or 2 acyl chains and phosphate group)
Triacylglycerol (3 acyl chains)
Phospholipid
Glycolipid (acyl chains linked to carb mol)
Steroids (ring structure)
Types of fatty acids?
Saturated FA are solid, no double bonds (high Tm)
Unsaturated FA – one or more double bonds that kink the hydrocarbon chain, liquid (low Tm)
What does 18:1(9) mean?
18 carbons and one double bond at position 9
What are the essential fatty acids?
Linoleic and a-linolenic; must get these from plants
What are the ‘good’ fats? (cardiovascular)?
high in polyunsaturated fatty acids: e.g. vegetable oils, like olive oil, sunflower oil, etc
What are the ‘bad fats’ (cardiovascular)?
high in saturated fatty acids: e.g. stearic (beef). (Saturated -major role in myelination of nerve fibres and hormone production important in maintaining health).
What are the really bad fats?
trans fatty acids, result from hydrogenation of vegetable oils e.g. hard margarine (man-made)
Why are essential fatty acids essential?
Humans cannot introduce double bonds beyond carbon 9
Must ingest essential FA
What other fatty acids are made from linoleic and linolenic acids?
Arachidonic acid, a precursor of eicosanoids can be synthesized from linoleic acid
Omega-3 fatty acids are derived from linolenic acid as essential FAs.
Omega-3 FA lowers plasma cholesterol prevents atherosclerosis, lowers TAG prevents obesity, reduces inflammation.
Effects of essential fatty acid deficiency?
Rare, occurring most often in infants fed dietsdeficientin EFAs.
Signs include scaly dermatitis, alopecia, thrombocytopenia, and, in children, intellectual disability.
People with chronic intestinal disorders
Can result in depression-deficiency of lipid signalling molecules
ADHD –lower levels of omega3 leads to behavioural problems
Characteristics of triaglycerols?
3 carbon backbone (glycerol) and 3 acyl chains
Esters of FAs and glycerol
Esters are neutral uncharged lipids
Water insoluble TAG coalesce into lipid droplets in adipose tissue (major lipid component of adipose tissue)
Dietary fuel and insulation
What does it mean by a phopsholipid being amphipathic?
Composed of glycerol bonded to two fatty acids and a phosphate group.
Charged phosphate ‘head’ group of a phospholipid is hydrophilic (attracted to water).
Hydrophobic ‘tails’ repel water.
Functions of phospholipids?
Membranes
Lipid droplets
Local signalling molecules
What are the 3 main classes of steroids?
Cholesterol is the starting material for the synthesis of bile salts, steroid hormones and other components
Steroid hormones are substances that serve as chemical messengers in the body (corticosteroids, sex hormones).
Bile salts: sodium salts of steroids used for emulsification
What are the functions of cholesterol, where it is made and where found?
-component of cell membranes
-precursor to other substances like sterol hormones, vitamin D and bile acids
-mainly made in liver and found only in animal foods
What are function of statins?
Inhibit HMG-CoA reductase that is essential in cholesterol synthesis
Lowers Low Density Lipoprotein (LDL) levels
Reduce risk of developing cardiovascular disease
Characteristics of Eicosanoids?
Lipid class derived from 20-carbon unsaturated fatty acids (eicosanoic acids) and are synthesized throughout the body
Signaling molecules derived from omega-3 or omega-6 fatty acids.
Precursors to prostaglandins, thromboxanes, and leukotrienes.
Short half life (metabolised rapidly), produced and act locally
What do eicosanoids regulate?
Lipid Inflammatory response (e.g. joints, skin, eyes)
Pain & fever (prostaglandins)
Blood pressure regulation (prostacyclin)
Blood clotting induction/platelet homeostasis (thromboxanes)
Many reproductive functions (e.g. labour induction) & menstrual cramps, sperm mobility (prostaglandins)
SMC constrictions & bronchioconstriction (leukotrienes)
Mucus production in the stomach (prostaglandins)
What is the main dietary lipid and other lipids ?
triaglycerol and phospholipids, cholesterol, cholesterol ester, free fatty acids
Where is main site of digestion?
small intestine
What is the main enzyme to break down lipids?
pancreatic enzymes (lipases) promoted by emulsification (dispersion) by bile salts and peristalsis (mixing)
Characteristics of bile salts?
Act as biological detergents to form emulsions and mixed micelles
Saves lipids coalescing in an aqueous environment
Derivatives of cholesterol
Steps of the digestion of lipids? (small intestine)
Most TAG degraded in small intestine by pancreatic lipase to monoacylglycerol and two fatty acids (FA)
Cholesterol esters digested to cholesterol and free FA
Phospholipids hydrolysed to FA and lysophospholipid
Digestion of lipids steps (basic)?
fat to emulsified fat through bile acids
emulsified fats to fatty acids and glycerol through lipases
How are digested lipids uptaken into cells?
Products of lipid digestion form mixed micelles with bile salts. Mixed micelles approach brush border membranes of enterocytes and release lipid products which enter cells by diffusion.
Short and medium chain FA do not require micelles for absorption
What is steatorrhea?
Lipid malabsorption due to defects in bile secretion, pancreatic function or intestinal cell uptake results in steatorrhea
Steatorrhea is excess fat in faeces. Stools float due to excess lipid, have an oily appearance and are foul smelling
Gallbladder secretes bile. Removal of the gallbladder inhibits digestion and absorption of fats
What happens to absorbed fatty acids?
Intestinal cells resynthesize TAG, PL, CE (lipids) for export
FAs are insoluble so packaged with apoB-48 (solubilising protein) into chylomicrons for export
Chylomicrons are released by exocytosis into lymph then blood
What happens when blood chylomicrons reach tissue?
TAG in chylomicrons is hydrolysed to FA and glycerol by lipoprotein lipase
Lipoprotein lipase is found primarily in capillaries of skeletal muscle and adipose tissue
Resulting free FA used for energy or re-esterified to TAG for storage
Chylomicrons depleted of TAG are called chylomicron remnants which go to the liver
Glycerol is used by liver to produce glycerol-3-phosphate (glycolysis & gluconeogenesis)
How are fatty acids transported in blood?
Free fatty acids transported through blood in complex with serum albumin
(sometimes called non-esterified fatty acids or NEFA)
Albumin most abundant plasma protein with 2-7 binding sites for FA
Most FA (>90%) is esterified (ie not free)
Esterified FA are carried in lipoproteins
Characteristics of lipoproteins?
Hydrophobic core: TGs, chloesteryl esters
Hydrophillic surfaces: Unesterified cholesterol, phospholipids, apolipoproteins e.g.B100
Lipoprotein classes?
Classified by density (least to most)
most dense are smallest
Chylomicrons: TAG rich (TAG from intestine to tissues).
VLDL: TAG rich (transports TAG from liver to tissue)
LDL: Cholesterol rich (cholesterol to extrahepatic tissue = BAD cholesterol)
HDL: Protein & cholesterol rich (cholesterol from tissue to liver for elimination = GOOD cholesterol)
What leads to atherosclerosis?
Too much LDL (obesity or genetic defect in LDL receptors) leads to atherosclerosis
Lipid develops into fatty streaks and plaque within artery
