Lecture 5 Flashcards
Topic: cholesterol metabolism.
Used as a paradigm to learn how nutrients regulate gene function.
Endogenous source od cholesterol.
De novo synthesis from acetyl-CoA; it comes from the TCA cycle, so all cells can do this. Anything from the outside is viewed as excess cholesterol that can overwhelm the system.
Exogenous source of cholesterol.
From the diet: animal products.
Endogenous cholesterol pathway.
Acetyl-CoA produces HMG-CoA. HMG-CoA conversion to mevalonic acid by HMG-CoA reductase is the rate limiting step.
Statins.
They inhibit HMG-CoA reductase activity, which shuts down cholesterol biosynthesis.
Site of cholesterol synthesis.
The ER.
Exogenous source of cholesterol.
Meat and animal products.
Digestions.
Enzymes in the saliva break down the food, the stomach hydrolyzes the food, the pancreas sends in more hydrolytic enzymes. result: the food is used to produce ATP.
Excess lipids.
The liver can repackage excess lipids from the intestine and send it back into the blood, where the process repeats, but in the absence of chylomicrons this time.
Storage of excess fat.
Converted into triglycerides and deposited in fat tissue.
Adipocytes.
Specialized for converting excess fatty acids to triacylglycerol and storing it; this type of cell has a propensity to store fat easily, which is why weight loss is a long-term process.
Bile acids.
Made in the liver, act as detergents in the intestine.
Lipases.
Important in the digestion of lipids.
Lipids.
Anything that does not dissolve in water.
Bile acids are made from cholesterol through 4 processes.
Hydroxylation of the sterol, epimerization.
Which is the only organ capable of making bile acids?
The liver.
Structure of bile acids.
Short (24 carbons), and all of those synthesized from the liver have glycine or taurine. Hydroxyl groups are located at carbon 7 and carbon 12. All polar molecules are located in one plane (hydrophilic plane and hydrophobic plane; this is why they act as detergents).
Fate of diet-derived lipids.
Hydrolyzed to the simplest forms in the lumen so they can be absorbed and re-synthesized into their molecular form.
Enterocytes.
Cells that line the intestinal tract.
Hydrolysis of lipids.
How lipids are cleaved has an important impact on the bioactivity of the metabolites it will produce; it is one way to make signalling molecules. Level of cellular control: you can even tailor the simple components produced from the hydrolysis.
What is located between the cell and the intestinal lumen?
An unstirred water layer.
Lipoproteins.
Non-covalent complexes between lipids and proteins.
Apolipoproteins.
Apo A, B, D, etc.
Structural apolipoproteins.
Apo A and Apo B.
