Cholesterol
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Which 3 sources are fats derived from
Diet De novo biosynthesis Adipose tissue
Which group of enzymes break down dietary fats?
Lipases
What is the role of bile salts?
To emulsify fats aiding digestion and absorption (also of fat-soluble vitamins)
Which vitamins are fat soluble?
A, D, E and K
What is the result of lack of bile salts?
Majority of fat passing the gut undigested resulting in steatorrhea (fatty stool)
What is steatorrhea?
Excretion of fatty stool due to incomplete digestion of fats
Where is bile salt produced and stored?
Produced in liver, stored in gallbladder
What is the oral medication that is effective in treating obesity by inhibiting gastric and pancreatic lipases called?
Orlistat aka tetrahydrolipstatin
How does orlistat help with weight loss?
Reduces fat absorption by 30% as it is a potent inhibitor of gastric and pancreatic lipase
What are the side effects of orlistat?
Main side effects include abdominal pain, urgency to defecate, increased flatus and steatorrhea
What is synthesised as a transport molecule for dietary fats?
Chylomicron (CM)
What is a CM composed of?
Triglycerides, apoproteins (from HDL) and phospholipids (enclosing the triglycerides)
What is the route CM follow?
travel from the lacteals of the intestine to the thoracic duct and to the left subclavian vein where they enter the bloodstream
Which enzyme hydrolyses CM?
Lipoprotein lipase through recognition of apoproteins
Where is lipoprotein lipase found?
Located on the capillary endothelial cells lining a variety of tissues including adipose, heart and skeletal muscle
What happens to the contents of CM after hydrolysis?
Triglycerides → FA and Glycerol FA undergo β-oxidation Glycerol returned to liver for gluconeogenesis
What type of lipids is cholesterol?
Steroid
Where is majority of cholesterol located in?
More than 90% of cholesterol in the body is found in cell membranes regulating membrane stiffness bidirectionally
What is the dietary cholesterol uptake limit in humans approximately?
0.5 g/day
How are the physiological requirements for cholesterol supplied?
De novo synthesis of cholesterol from Acetyl CoA in the liver
What is the first of 3 main parts of cholesterol biosynthesis?
Synthesis of isopentenyl pyrophosphate, an activated isoprene unit which serves as a key building block (cytoplasm)
What is the second of 3 main parts of cholesterol biosynthesis?
Condensation of six molecules of isopentenyl pyrophosphate to form squalene (cytoplasm)
What is the third of 3 main parts of cholesterol biosynthesis?
Cyclisation and demethylation of squalene by monooxygenases to give cholsterol (ER)
Cholesterol Biosynthesis Identify the step, enzyme and product
Step 1
