Lipids 1 Flashcards
Name the classes of lipids.
Fatty acids
Triacylglycerols
Phospholipids
Glycolipids
Steroid
Describe essential fatty acids.
Essential fatty acids need to be ingested (from plants) as the human body cannot introduce double bonds beyond carbon 9.
e.g. linoleic acids, alpha-linoleic acid.
Describe the importance of omega-3 fatty acids.
They are derived from linoleic acids as essential fatty acids.
They lower plasma cholesterol, which prevents atherosclerosis.
They lower TAG, prevent obesity and reduce inflammation.
Describe “good fats” from our diet.
Good fats are high in polysaturated fatty acids.
e.g. veggie, olive and sunflower oil.
Describe “bad fats” from our diet.
Bad fats are high in saturated fatty acids.
e.g. stearic (beef).
Describe “really bad fats” from our diet.
High in trans fatty acids, and are a result from hydrogenation of vegetable oil.
e.g. margarine (man-made).
What are the biological functions of lipids?
Stored form of energy
Signalling molecules
Enzyme cofactors
Vitamins
Structural elements in membranes
Describe triacylglycerols.
TAGs are esters of fatty acids and glycerol/ neutral uncharged lipids.
They are water insoluble
They are the major lipid component of adipose tissue and exist here as lipid droplets.
They act as a dietary fuel and insulation (keep us war, and insulate electrical signals).
Describe phospholipids.
Phospholipids are amphipathic molecules.
They consist of glycerol + 2 fatty acids + an inorganic phosphate group.
The charged phosphate head is hydrophilic.
The tails are hydrophobic (lipophilic).
They are critical for simultaneous aqueous and non-aqueous interfaces; membranes, lipid droplets, local signalling molecules.
Describe steroids as lipids.
Steroids are a major class of lipids, they have a ring structure.
There are three main classes:
Cholesterol, Steroid hormones and Bile salts.
Give the functions of bile salts and steroid hormones as steroids.
Bile salts - Sodium salts of steroids used for emulsification
Steroid hormones - Serve as messengers in the body.
Describe the main functions of cholesterol in the body.
Precursor of other substances: bile salts (in liver), steroid hormones, vitamin D, lipoproteins, membranes.
They can also modify proteins.
Describe the synthesis of cholesterol.
Cholesterol is made mainly in the liver, and begins with Acetyl CoA (which comes from glycolysis, amino acids or fatty acids).
Acetyl CoA is converted to HMG-CoA.
HMG-CoA is converted to Mevalonate by the enzyme HMG-CoA reductase. (this is the rate determining step and is targeted by statins).
Mevalonte is converted to isoprene units.
Isoprene units are converted to Squalene.
Squalene is converted to Cholesterol.
Describe the role of statins in the regulation of cholesterol biosynthesis.
Statins inhibit HMG-reductase.
They lower the LDL levels
= reduce the risk of developing cardiovascular disease.
Describe the structure of cholesterol.
Cholesterol has a central sterol nucleus of 4 hydrocarbon rings.
It has a hydrocarbon tail and a hydroxyl group.
This structure makes it hydrophobic meaning it cannot flow through the blood stream alone.
Describe the structure of eicosanoids.
Eicosanoids are a lipid class derived from 20 carbon unsaturated fatty acids (eicosanoid acids) and are synthesised throughout the body.
Describe the function of eicosanoids as precursors.
They are precursors to:
Prostaglandins
Thromboxanes
Leukotrienes.
They are metabolised quickly due to their short half life, and are produced and act locally.
What do eicosanoids regulate?
Lipid inflammatory response
Pain and fever (prostaglandins)
Blood pressure regulation (prostacyclin - inhibits platelet activation and dilates blood vessels)
Blood clotting induction/platelet homeostasis (thromboxanes)
Many reproductive functions (prostaglandins)
SMC constrictions and bronchoconstriction.
Mucus production in stomach (prostaglandins)
Describe the importance of eicosanoids in medicines.
Eicosanoids can induce lipid inflammatory effects so their regulation is important in drugs.
Describe how synthesis of eicosanoids is regulated.
The synthesis of eicosanoids is regulated by cyclooxygenase (COX) 1 and 2, (for prostanoids).
The synthesis of Hetes (leukotrienes and lipoxins) is regulated by LOX.
Describe the synthesis of prostanoids.
All eicosanoids synthesis starts with arachidonic acid being esterified in the membrane phospholipid.
An enzyme called phospholipase A2 cleaves the phospholipid to produce arachidonic acid.
Arachidonic acid is then converted by a two-step reaction pathway involving COX 1 and COX 2 enzymes.
Describe the synthesis of hetes.
All eicosanoids synthesis starts with arachidonic acid esterified in membrane phospholipid.
An enzyme called phospholipase A2 cleaves the phospholipid to produce arachidonic acid.
Arachidonic acid is then converted by a linear pathway, initiated by members of the LOX family of enzymes.
Describe the process of lipid digestion.
Lipids are digested by pancreatic enzymes (lipases) and is promoted by emulsification (dispersion) by bile salts and peristalsis (mixing).
This process occurs in the small intestine, where fat is converted to emulsified fats and are then broken down further into fatty acids and glycerol (by lipases).
Describe the role of bile salts in lipid digestion.
Bile salts (2 major: taurocholic and glycholic) act as biological detergents to form emulsions an mixed micelles.
This saves lipids coalescing in an aqueous environment.
Describe the digestion of triacylglycerol.
Triacylglycerol is digested by pancreatic lipase, which removes 2 fatty acids from Carbon #1 and #3.
This removal produces monoacylglycerol and 2 fatty acids.
Describe the digestion of cholesterol esters.
Cholesterol esters are digested to cholesterol and free fatty acids.
Describe the digestion of phospholipids.
Phospholipids are hydrolysed to fatty acids and lysophospholipid.
Describe the process of the uptake of lipids into cells, after digestion.
Products of lipid digestion form mixed micelles with bile salts, this allow them to be transported by the hydrophobic part of the bile salt. Mixed micelles approach the brush border membranes of enterocytes and release lipid products which enter these cells by diffusion.
*(short and medium fatty acids do not require micelles for absorption)
Describe what happens to lipids once absorbed by enterocytes.
Intestinal cells resynthesise triacylglycerol, phospholipids and cholesterol esters for export
Fatty acids are insoluble so are packaged with a solubilising protein into chylomicrons for export.
Chylomicrons (lipoproteins) are released by exocytosis into lymph and then blood.
Define a lipoprotein.
A lipoprotein consists of lipid particles coated with phospholipids to allow process round body.
Describe what happens to lipids such as TAG when transferring from blood to tissue.
The TAG containing chylomicron si hydrolysed to Fatty acids and glycerol by lipoprotein lipase (this is found primarily in the capillaries of skeletal muscle and adipose tissue).
The resulting free fatty acids are used for energy or are re-esterified to TAG for storage.
What happens to chylomicrons once they are depleted of the lipid they were exporting.
Chylomicrons depleted of lipid (TAG) are called chylomicron remnants which go to the liver.
Glucose is used by the liver to produce glycerol - 3 phosphate (glycolysis, gluconeogenesis).
Describe the transport of fatty acids through blood.
Fatty acids are transported through blood in complex with serum albumin (non-esterified).
Esterified fatty acids are carried in lipoproteins.
Give examples of the classes of lipoproteins.
Classified by density: least to most dense-
Chylomicrons (TAG rich, transports from intestine to tissue)
VLDL (TAG rich, transports from liver to tissue)
LDL (Cholesterol rich, transports to extrahepatic tissue)
HDL (protein and cholesterol rich, from tissue to liver for elimination = good cholesterol)
Define atherosclerosis.
Atherosclerosis is a gradual build up of plaque on the arteries.
This can be due to unhealthily high cholesterol levels that can come from too much LDL
