Lipids 1 Flashcards
What are lipids?
Heterogeneous organic molecules that are insoluble in water but soluble in organic solvents.
What forms can lipids take?
- Phospholipids in cell membranes
- Lipid droplets in adipose tissue
- Lipoproteins in blood
What are the biological functions of lipids?
- Stored form of energy
- Structural element of membranes
- Enzyme cofactors
- Hormones
- Vitamins A,D,E,K
- Signalling molecules
What are the 5 lipid classes?
- Fatty acids
- Tracylgycerol
- Phospholipid
- Glycolipid
- Steroids
Describe unsaturated FA.
- Contain one or more double bonds that kink the hydrocarbon chain
- Liquid
- Low Tm
Describe saturated FA.
- No double bonds
- Solid
- High Tm
What does 18:1 mean in FA nomenclature?
18 carbons and 1 double bond
What is the terminal methyl group?
Omega carbon
What are the 4 kinds of FA?
- Essential FA
- Good fats
- Bad fats
- Really bad fats
What are essential FA/
Linoleic and a-linolenic which we must get from plants
What are good fats?
- High in polyunsaturated FA
- Vegetable oils, olive oil, sunflower oil
What are bad fats?
- High in saturated FA
- stearic (beef)
What are really bad fats?
- Trans FA which are a result of hydrogenation of vegetable oils
- Hard margarine
What do saturated fats play a huge role in?
Myelination of nerve fibres and hormone production
Why must we ingest essential FA?
Humans are not capable of introducing double bonds beyond carbon 9
What is arachnoid acid?
A precursor of eicosanoids which can be synthesised from linoleic acid.
What is linoleic acid a substrate for?
Prostaglandins
What is omega-3 FA derived from?
Linolenic acid
What are examples of Omega-3 FA?
- Eicosapentaenoic acid
- Docosahexaenoic acid
What do Omega-3 FA do?
- Lowers plasma cholesterol preventing atherosclerosis
- Lowers TAG preventing obesity
What are Omega-6 FAs?
- Derived from linoleic
- Essential but not the same benefits as omega-3
What are the symptoms of essential fatty acid deficiency?
- Growth retardation
- reproductive failure
- Skin lesions
- Kidney and liber disorders
- Subtle neurological and visual problems
What conditions are linked to essential FA deficiency?
- Chronic intestinal diseases
- Depression
- ADHD
What is TAG?
- Triacylglycerol/ triglyceride
- Esters of FAs and glycerol
- Dietary fuel and insulation
- Esters are neutral uncharged lipids
- Water insoluble, TAG coalesce into lipid droplets in adipose tissue
What are phospholipids composed of?
-Glycerol bonded to 2 FA and a phosphate group
Amphipathic
Charged phosphate group head of a phospholipid id hydrophilic whereas the hydrophobic tails repel water
What is the main dietary lipid?
TAG
What are other dietary lipids/
- Phospholipids
- Cholesterol
- Cholesterol ester
- Free FA
What is the main site of lipid digestion?
Small intestine
What are the main mechanisms involved in the digestion of lipids?
Lipid digestion by pancreatic enzymes (lipases) is promoted by emulsification (dispersion) by bile salts and peristalsis
What do bile salts do?
- Act as biological agents to form emulsions
- Saves lipid coalescing in an aqueous environment
- Derivatives of cholesterol
How is TAG broken down?
Most TAG is degraded in the small intestine by pancreatic lipase to monoacylglycerol and 2 FA
What are cholesterol esters digested to?
Cholesterol and free FA
What are phospholipids hydrolysed to?
FA and lysophospholipid
What do the products of lipid digestion from?
Mixed micelles with bile salts
What happens to the mixed micelles?
They approach the brush border membranes of enterocytes and release lipid products which enter cells by diffusion
What do not require micelles for absorption?
Short and medium chain FA
What is steatorrhea?
Excess fat in faeces. Stools float due to excess lipid and have an oily appearance and foul smell
What causes steatorrhea?
Lipid malabsorption due to defects in bile secretion, pancreatic function or intestinal call uptake
What role does the gallbladder play in lipid absorption?
It secretes bile. Removal of the gallbladder inhibits digestion and absorption fats
What happens to absorbed FA?
- The intestinal cells resynthesize TAG, phospholipids and cholesterol esters for export.
- They are insoluble so are packaged with apoB-48 into chylomicrons for export.
- Chylomicrons are released by exocytosis into lymph then blood
What is apoB-48?
Solubilising protein
What does lipoprotein lipase do?
Hydrolyses TAG in chylomicrons to FA and glycerol
Where is lipoprotein lipase found?
Primarily in capillaries of skeletal muscle and adipose tissue
What happens to the FA TAG is hydrolysed?
Used for energy or re-esterified to TAG for storage
What happens to chylomicrons depleted of TAG?
They are call chylomicron remnants and they go to the liver
What does the liver do to glycerol?
Uses it to produce glycerol-3-phosphate for us in glycolysis and gluconeogenesis
What is TAG stored as in adipose tissue?
Droplets that constitute depot fat
Why is TAG the most efficient form of storage fuel?
It is highly reduced and nearly anhydrous
How are FA released from stored TAG?
By the action of HSL (hormone sensitive lipase)
What activates HSL?
Phosphorylation in response to epinephrine
What promotes the dephosphorylation and consequent inactivation of lipase?
High plasma glucose and insulin
How are free FA transported in the blood?
In a complex with serum albumin
What is albumin?
The most abundant plasma protein
What are esterified FA in the blood carried in?
Lipoproteins
Describe the structure of a lipoprotein.
- Hydrophobic core made of TAG and cholesterol esters
- Hydrophilic surface made of unesterfied cholesterol, phospholipids and apolipoproteins
Liporotein classes according to density.
Least dense to Most dense
- Chylomicrons: TAG rich (TAG from intestine to tissues)
- VLDL: TAG rich (TAG from liver to tissue
- LDL: cholesterol rich (cholesterol to extrahepatic tissue)
- HDL: protein/cholesterol rich (transports cholesterol from tissue to liver for elimination)
What does too much LDL lead to?
- Artheroscolosis
- Lipid develops into fatty streaks and plaque within artery
