Lipids Flashcards
Where do Lipids exist?
- Phospholipids in cell membranes
- As lipid droplets in adipose tissue
- As lipoproteins in blood
Are Lipids soluble in water?
No, lipids are insoluble in water (hydrophobic). They are soluble in organic solvents.
Name 6 biological functions of lipids?
- A stored form of energy
- A structural element of membranes
- Enzyme Cofactors
- Hormones
- Vitamins A,D,E,K
- Signalling Molecules
Name 5 Classes of Lipid:
- Fatty Acids
- Phospholipids
- Steroids
- Glycolipid
- Triacylglycerol
What is the makeup and function of Glycolipids?
They contain Carbohydrate and Lipid
They are components of membranes and nerve tissue and a source of antigens that give blood groups.
Define Saturated and unsaturated Fatty Acids:
Saturated FA have no double bonds and so are striaght and have a high melting point
Unsaturdated FA have 1 or more double C=C bonds which produces kinks in the chain and gives them a low melting point.
Explain Linoleate 18:2(9,12)
The FA is Linoleate. its made up of an 18 carbon chain containing two double bonds at carbons 9 and 12. The carbons are counted from the carboxyl group.
Which fatty acids are “good and which are “bad”?
“good” fats are high in polyunsaturated FA such as ovlive oil and veg oil.
“bad” fats are high in saturated fatty acids such as stearic acid in beef.
What are Essential FA?
Essential fatty aids cannot be produced in the human body (beacue the body lacks the enzymes to introduce double bonds beyond carbon 9) so must be gained from eating plants. (e.g. Linoleic and alpha-linoleic acid.
Explain Omega-3 FA:
Omega-3 fatty acids are derived form linolenic acid and are essential FAs wich lower plasma cholesterol to prvent atherosclerosis and lowers TAG to prevent obesity.
Explain Omega-6 FA
Derived from linoleic acid and essential.
What does Essential FA deficiency Cause?
Kidney and liver disorders, skin lesions, growth retardation etc. Also linked to depression and ADHD.
Explain 4 properties of TAG:
Esters of FAs and glycerol
- Neutral uncarged lipids
- Water insoluble (coalesce into lipid drops in adipose tissure)
- Dietary fuel and insulation
What makes up Phospholipids?
Glycerol, a phosphate group and two FA
Explain the term amphitatic:
Charged phosphate group (head) is hydrophilic and the ‘tail’ is hydrophobic, repels water.
How are Lipids Digested?
Short chain lipids are digested in the stomach by acid lipases.
The small intestine is the main site of lipid digestion by pancreatic enzymes (lipases), it is promoted by emulsification (dispersion) by bile salts and peristalsis (mixing).
What are bile salts and what is their function?
Bile Salts are derivatives of cholesterol
They act as biological detergents to form emulsions and mixed micelles, in order to stop lipids coalescing in an aqueous enviroment (like the intestine).
How are TAGs digested?
Triacylglycerides are degraded by pancratic lipase in the small intestine to monoacylglycerol + 2 FA.
How are Cholesterol Esters digested?
To cholesterol and Free FA
How are Phospholipids digested?
Hydrolysed to FA and lysophospholipid.
Define general lipid digestion?
Bile salts form emulsified fats from fats
Pancreatic lipases then break the emulsified fats down into fatty acids and glycerol
How are digested lipids taken up?
Fatty Acids and glycerol form mixed micelles with bile salts, they travel to microvilli in the intestine an release the products which enter the epithelial tissue by diffusion.
(Short and Medium chain FA dont need micelles)
What is Steatorrhea, how does it come about?
Steatorrhea is excess fat in faeces causing it to float, smell and have an oily appearence.
It occurs because lipid products are insufficently taken up by intestinal cells due to defects in bile secretion, pancreatic function or intestinal cell uptake.
It can also be caused by removal of the all bladder which secretes bile.
Use of dietary lipids:
Intestinal cells resynthetise TAG, PL etc for export
- Packaged into chylomicrons with solubilising protein because theyre insoluble.
- Chylomicrons enter lymph then blood by exocytosis.
Chylomicrons in tissue?
TAG os hydrolyed to FA and glycerol by lipoprotein lipse (found in capillaries and adipose tissue), the resulting free FA is used for energy or reesterified for storage.
Depleted chylomicrons are called chylomicron remnants and return to the liver.
How is TAG stored?
In Adipose cells as droplets that constiute “depot fat”. TAGs a very effiencent storage form of fuel, very reduced and anhydrous.
How is stored TAG used?
- HSL activated by phosphorylation in response to epinephrine
- Hormone sensitve Lipase (HSL) realeased FA
- High plasma lucose and insulin levels then cause dephosphorylation (inactivation) of the HSL
How is free FA transported in the blood?
- Free FA is transported in a complex with serum albumin (the most abundant plasma protein, containgin 2-7 sites for FA binding.)
- Most FA isnt free but esterified and carried in lipoproteins
Name 4 classes of lipoproteins in increasing density order:
Chylomicrons, VLDL, LDL, HDL
What are chylomicrons rich in and where do they carry it?
Chylomicorns are rich in TAG and carry it from the intestine to Tissues.
What is VLDL rich in and where does it carry it?
VLDL is rich in TAG and carries it form the liver to tissues.
Whats LDL rich in?
LDL is rich in cholesoerol and carries it to extrahepatic tissue/
What is HDL rich in?
Proteins and cholesterol, it transports cholesterol from tiissues to the liver for elimination.
What causes excessive LDL and what does it cause in turn?
Obesity or a genetic defect in LDL receptors acauses excessive LDL buildup.
This leads to atherosclerosis through the build up of fatty streaks and plaque in the arteries.
