Lipids Flashcards
What are the functions of lipids within the body?
- Storage of energy
- Structural component of cell membranes
- Signalling molecules
- Hormones
- Vitamins A,D,E and K
- Enzyme Cofactors
What are the 5 main classes of lipids?
- Fatty acids
- Triacylglycerol
- Phospholipids
- Glycolipids
- Steroids
What are essential fatty acids?
Fatty acids which must be taken in the diet from plants.
E.g. linoleic and alpha linoleic
What is meant by BAD fats?
Fats with a high saturated fat content
What is meant by GOOD fats?
Fats with a high polyunsaturated fat content.
E.g. vegetable oil
What is meant by trans fats?
Man made saturated fats from the hydrogenation of unsaturated fats.
What is the difference between saturated and unsaturated fats.
Unsaturated fats contain C=C, resulting in kinks in the fatty acid chain. This leads to a decrease in melting point. These fats are liquid at room temp.
Saturated fats do not contain double bonds. As a result, they have a straight chain and so a higher melting point. They are solid at room temperature.
What is the major health benefit of omega-3 intake?
Omega-3 (derived from linoleic acid) lowers plasma cholesterol, to prevent atherosclerosis.
How are triacylglycerols formed?
Esterification of 3 fatty acids with a glycerol molecule.
How are phospholipids formed?
Esterification of one glycerol molecule with 2 fatty acids and a phosphate molecule.
Why are phospholipids considered amphipathic molecules?
They contain a hydrophilic (phosphate) head and a hydrophobic (fatty acid) tail
What is the role of bile salts on lipid digestion?
Bile salts act as biological detergents, forming emulsions and allowing mixed micelles.
What are the digestive products of triacylglycerols?
Monoacylglycerol and 2 Fatty acids
Where is the main site of digestion of TAGs?
Small intestine
What are the products of phospholipid digestion in the body?
Lysophospholipid and one fatty acid
What are the products of cholesterol ester digestion in the body?
Cholesterol and free fatty acid
What is steatorrhea and why does it occur?
Steatorrhea is excess fat in the stool and is caused by lipid malabsorption due to defects in bile secretion, pancreatic function or intestinal cell uptake
What path is taken by the digestive products of triacylglycerols?
- Fatty acids and glycerols are taken up by intestinal mucosa
- Used to resynthesize TAG.
- TAG insoluble and so packaged into chylomicrons for transport
- Transported to blood stream via lymphatic system
- TAG in chylomicron is hydrolysed to FAs and glycerol
- FAs enter cells and are either utilised as a fuel source or esterified to TAG for storage.
- Glycerol is used by the liver to synthesis Glycerol-3-phosphate for glycolysis/ gluconeogenesis
What enzyme is used to release FA from stored TAG?
Hormone sensitive lipase (HSL)
Where does B oxidation occur?
Cytosol and Mitochondrial matrix
What is the aim of B oxidation?
To degrade fatty acid molecules 2 carbons at a time to create acetyl CoA and reduced NAD and FAD
What are the three main steps to B oxidation?
- Activation of FA to form Fatty acyl CoA
- Transport of longer chain fatty acyl CoA from cytosol to mitochondrial matrix via carnitine shuttle
- Degradation of fatty acyl CoA to form 2C acetyl CoA
What substance inhibits carnitine shuttle function and why?
Malonyl CoA inhibits Carnitine shuttle function.
Malonyl CoA is required for fatty acid synthesis and so it prevents synthesis and degradation occurring simultaneously.
How many reduced NAD/ FADs are produced per B oxidation reaction?
One NADH and one FADH2
Palmitate is a fatty acid with 16 Carbons. How many B oxidation reactions are required to degrade it into 8 acetyl CoA molecules?
7
What two routes can the acetyl CoA from B oxidation take?
- Mainly it enters the Citric Acid cycle
2. However, when it is in excess it can be used in ketogenesis to create ketone bodies?
How are ketone bodies utilised in the body?
They can be used as a fuel source for the brain, cardiac and skeletal muscle in times of starvation
Where exactly in the body are ketone bodies formed?
Mitochondrial matrix of liver cells.
In what body tissue does fatty acid synthesis occur?
- Liver
- Lactating mammary glands
- Adipose tissue
Where in the cell does Fatty Acid synthesis occur?
Cytosol
By what mechanism is acetyl CoA from the mitochondria transported to the cytosol?
Citrate shuttle
Describe the mechanism of action of the citrate shuttle in fatty acid synthesis.
- Acetyl CoA in the mitochondria drops acetyl group (2C fragment)
- Acetyl group is picked up by oxaloacetate to form citrate
- Citrate shuttles to the cytosol
- Drops acetyl group in cytosol and is used to synthesis pyruvate.
- Pyruvate shuttles back to mitochondrial matrix and is used to resynthesise oxaloacetate
What is the product of fatty acid synthesis in the body?
Palmitic acid
What two enzymes are used for fatty acid synthesis in the body?
Acetyl CoA carboxylase
Fatty acid synthase
How many acetyl CoA molecules are required to synthesis one molecule of palmitate?
8
How many NADPH molecules are required for the synthesis of one palmitate molecule?
14
What carrier protein is used in fatty acid synthesis?
ACP (Acyl carrier protein)
What can cholesterol be used in the synthesis of?
Plasma lipoproteins Membranes Vitamin D Steroid hormones Bile salts
What are the four classes of lipoproteins?
Chylomicrons
LDL
HDL
VLDL
In Beta oxidation, how many reduced FADs and NADs are produced per acetyl CoA produced?
1 FADH2 and 1 NADH
