Phospholipids and sterols test 2

Question 1

Draw the structural formula of cholesterol. Describe its properties and transport in animal organisms

Answer 1

Properties:
Hydroxyl group on the C3. The presence of a hydroxyl group makes cholesterol slightly hydrophilic.
Double bond at the C5 carbon
Methyl group on the C13 and C10 carbon
At the C17 position there is a 8 carbon branched hydrocarbon substituent
Aliphatic chain
Transport:
Chylomicrons - the largest and least dense lipoproteins. They are formed in the intestine, from where they transport cholesterol to the liver.

VLDL (very low density lipoproteins) are produced in the liver; they are specialised in transporting lipids from liver to periphery tissues.

*LDL (low density lipoproteins) are the most important fraction transporting cholesterol from the liver to the other organs – kidneys, muscle and adrenal cortex, primarily. They contain most of the serum cholesterol.

*HDL (high density lipoproteins) are synthesized in the liver and released to the circulation due to exocytosis. HDL is considered as the main factor removing cholesterol from the serum. HDL actively absorbs free cholesterol from the membrane surface and circulating LDL lipoproteins. Circular HDL is absorbed by the liver through endocytosis, where esters of cholesterol are hydrolysed.

Question 2

What is the function of bile acids in animal organisms? Where and how are they converted to bile acids salts?

Answer 2

Bile Acids: Eliminate Cholesterol within the body
Bile Acid Salts:
Before leaving the liver, bile acids are conjugated with the amino acids glycine or taurine to form bile salts. Bile acid salts are stored and concentrated in the gallbladder before being released into the small intestine.

Question 3

What is the difference in composition and function of HDL and LDL?

Answer 3

HDL (high density lipoproteins) are synthetized in the liver and released to the circulation due to exocytosis. HDL are considered as the main factor removing cholesterol from the serum. HDL actively absorb free cholesterol from the membrane surface and circulating LDL lipoproteins. Circular HDL are absorbed by the liver through endocytosis, where esters of cholesterol are hydrolysed.

LDL (low density lipoproteins) are the most important fraction transporting cholesterol from the liver to the other organs – kidneys, muscle and adrenal cortex, primarily. They contain most of the serum cholesterol.

Question 4

What is the function of bile acids in animal organisms? Where are they synthesized and where do they act? Draw the structural formula of a chosen bile acid.

Answer 4

Eliminate Cholesterol within the body
Bile acids are organic acids synthesized in the liver and they are the final product of cholesterol metabolism.
They act in the intestines

Question 5

Draw the structural formula of cholesterol and describe its function in organisms

Answer 5

Function:
Component of cell membranes and plasma lipoproteins.
Makes hormones (Oestrogen, Progesterone, testosterone)
Produces vitamin D