Cholesterol Flashcards
What is cholestrol synthesised from?
Acetyl-CoA
Summarise the synthesis of Cholesterol from acetyl CoA
1)Synthesis of isopentenyl pyrophosphate, an activated isoprene unit which serves as a key building block (cytoplasm). 2)Condensation of six molecules of isopentenyl pyrophosphate to form squalene (cytoplasm). 3)Cyclisation and demethylation of squalene by monooxygenases to give cholsterol (ER).
Summarise the synthesis of Cholesterol into steriod hormones
The precursor pregnenolone is generated from cholesterol by the action of the enzyme desmolase. All 5 classes of steroid hormones come from pregnenolone:
What vitamin can be synthesised from cholesterol?
Vitamen D
What are bile salts made out of?
Bile salts are the major breakdown products of cholesterol
The insolubility of lipids in aqueous solutions poses transportation problems for the body How is this problem solved by the body?
lipis are packed within lipoproteins. add pic
What do lipoproteins consist of?
Lipoproteins are composed of a phopholipid monolayer containing cholesterol and proteins known as apoproteins Packed within the core of the lipoprotein are a mixture of cholesterol esters and triacylglycerols.
Name some forms of lipoproteins?
Low density lipoproteins (LDL) • High density lipoproteins (HDL)
Explain how fat is digested and absorbed
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What do micelles do?
Micelles are necessary because they transport the poorly soluble monoglycerides and fatty acids to the surface of the enterocyte where they can be absorbed. As well, micelles contain fat soluble vitamins and cholesterol.
What are Chylomicrons
Chylomicrons are transported via the lymohatucs into the bloodstream and broken down by the enzyme Lipoprotein lipase located on the capillary endothelial cells. The triacylglycerols within the chylomicrons are hydrolysed to glycerol and fatty acids, the latter undergoing beta oxidatiob. Glycerol is returned to the liver and used in gluconeogenesis Another explanation: Once inside the enterocyte, monoglycerides and fatty acids are re-synthesized into TAG. The TAG is packaged, along with cholesterol and fat soluble vitamins, into chylomicrons. Chylomicrons are lipoproteins, special particles that are designed for the transport of lipids in the circulation. You can review the structure of lipoproteins by visiting the web page on lipoproteins from fall quarter. Chylomicrons are released by exocytosis at the basolateral surface of the enterocytes. Because they are particles, they are too large to enter typical capillaries. Instead they enter lacteals, lymphatic capillaries that poke up into the center of each villus. Chylomicrons then flow into the circulation via lymphatic vessels, which drain into the general circulation at the large veins in the chest. Chylomicrons deliver absorbed TAG to the body’s cells. TAG in chylomicrons and other lipoproteins is hydrolyzed by lipoprotein lipase, an enzyme that is found in capillary endothelial cells. Monoglycerides and fatty acids released from digestion of TAG then diffuse into cells. add pic
What is the function of HDL?
HDLs are often referred to as “good cholesterol” as they function to take cholesterol from peripheral tissues back to the liver for use or disposal (reverse cholesterol transport). They help to lower total serum cholesterol.
What is the function of LDL?
LDLs are often referred to as “bad cholesterol” as prolonged elevation of LDL levels leads to atherosclerosis (hardening of the arteries). LDLs transport cholesterol synthesized in the liver to peripheral tissues with more than 40% of their weight made up of cholesterol esters.
What causes familial hypercholestrolaemia?
LDL are taken up by specific cell-surface receptors known as LDL receptors or LDLR in a process known as receptor mediated endocytosis. Mutations within the LDLR gene can result in the disease FH.
What does familial hypercholestrolaemia leave you more predisposed for?
atheroscelrosis - xanthomas add pic
