Molecular Biology - Cholestrol Flashcards
(50 cards)
3 main sources fats are derived from
Diet
De novo biosynthesis in the liver
Storage deposits in adipose
What are deitary fats broken down by?
Lipases
Where are bile salts generated and stored?
Liver and gallbladder respectively
Bile salts during digestion?
Pass from bile duct into intestine where they emulsify fats in the intestine, aiding their digestion and absorption of fats + fat-soluble vitamins
Lack of bile salts
Majority of fat passes through undigested resulting in steatorrhea (fatty stool)
Treatment for obesity
Orlistat is a gastric/pancreatic lipase inhibitor and derivative of lipstatin so reduces fat absorption
What type of lipoprotein has a role in dietary fat transport?
Chylomicrons - source is in the intestine
Anatomy of chylomicron?
Single phospholipid bilayer with apoproteins on outside and triglycerides in the middle
How is chylomicron created?
Digested dietary products are absorbed by enterocyte that line brush border ; triglycerides are resynthesized and transported via lymphatics
When do chylomicrons aquire apoproteins?
From HDL following release into bloodstream
Mechanism of action of chylomicron on heart/adipose/skeletal?
Binds to lipoprotein lipase and the fatty acids undergo beta oxidation while glycerol is returned to liver for gluconeogenesis
Special about chylomicrons?
Hydrophilic outside
Hydrophobic core
What type of molecule is cholestrol
Steroid
Cholestrol uptake/amount needed?
All physiological requirements for cholestrol are supplied by liver through de novo synthesis of cholestrol from acetyl-coA
Cholestrol synthesis
1 pathway 3 parts
1) Cytoplasm - isopentyl pyrophosphate synthesis
2) Cytoplasm - 6 molecules of step 1 condensation to form squalene
3) ER - cyclisation/demethylation of squalene gives cholestrol
Step 1 of step 1
Needs two Acetyl CoA molecules condensation and releases coA
Main step of step 1
When creating mevalonate ; HMG-CoA reductase is negative feedback loop by end product cholestrol and mevalonate/bile salts
What happens in main step?
NADPH is oxidised to NADP and coA is removed
(redox)
To finish off step 1?
Sequential phosphorylation and decarboxylation
Second step?
3 condensation reactions of 5 carbon unit structures to make a C15 molecule ; two of which condense to form squalene
Step 3
Cyclisation + demethylation
how is cholestrol basis of all steroid hormones?
It producs the precursor called pregnenolone by enzyme desmolase
5 classes of steroid hormones?
Glucocorticoids
mineralocorticoids
androgens
estrogens
progestagens
What can vitamin D deficiency lead to?
Rickets
