Lipid Metabolism Flashcards
What is the general structure of a triacylglycerol?
glycerol + 3 fatty acids
What is the general structure of a steroid?
4 carbon rings with R groups bound to rings (R group just means anything)
What is the general structure of a glycolipid?
glycolipid has a carbohydrate bound to the “head” of the glycolipid. Otherwise it is a pair of fatty acids bound to a polar nitrogenous head.
What is the general structure of a phospholipid?
phospholipid has a fatty acid tail, a phosphate bridge, and a nitrogenous head.
What is the general structure of a fatty acid?
A long chain of carbons and hydrogens, with a polar head. Can be saturated (all single bonds) or unsaturated (some double bonds). Double bonds can be cis (cause kinks) or trans (keep the molecule straight).
What lipid is used for energy storage?
Triacylglycerol! It’s efficient in terms of energy per unit weight, but it’s also super good for energy storage because it doesn’t require any hydration, whereas every gram of carbohydrate requires two grams of water for storage.
How does degree of unsaturation and size effect melting point for fats?
Melting point increases as length of fatty acid chain increases. Melting point decreases as degree of unsaturation increases. Trans double bonds cause less of a temperature decrease than cis. For a given length of fatty acid, the difference between cis and saturated can be 70 degrees!
Why are most fatty acids of even length?
Our fatty acid synthesis mechanisms add two carbon chains at a time, as do all animals. Since carbons are added 2 at a time, you always end up with an even chain fatty acid.
Where do odd-length fatty acids come from?
We don’t produce odd-length fatty acids, so they have to come in from the diet. We can’t digest odd-length fatty acids without an additional step that creates propionyl CoA and breaks it down to succinyl CoA (a step in the TCA cycle!) The succinyl CoA jumps straight into the TCA cycle to turn into succinate.
What are the alpha, beta, and omega carbons in a fatty acid?
The carboxyl carbon on a fatty acid is the 1st carbon. The next carbon (2nd) is the alpha carbon. The beta carbon is the 3rd carbon. This is where oxidation occurs (beta oxidation). The omega carbon is the last carbon on the fatty acid chain
Where are triacylglycerides stored?
Adipose cells are cells with basically giant vacuoles to hold lipids. Triacylglycerides form lipid droplets in the cell.
What issue arises with lipid digestion in the body?
The body is an aqueous environment. Lipids do not cope well in an aqueous environment. So the body needs to come up with a way to bring hydrophilic enzymes into interaction with hydrophobic lipids.
How does the body bring lipids and their regulatory enzymes together?
Lipid emulsification is defined as the process of maximizing the exposed surface area of lipids so enzymes can ultimately lead to lipid digestion. Emulsification has multiple pathways: chewing, intestinal peristalsis, and bile salts. These pathways maximize the availability of lipids for enzymes to interact with.
What enzymes digest lipids? How do they interact with the lipids?
Lipases break lipids down into smaller molecules. Lipases often utilize a colipase molecule to facility the interaction with lipids. Lipases are hydrophilic, but this colipase molecule has a hydrophobic domain for interacting with the lipid. It also binds the lipase and induces a conformation change. This conformation change pushes a regulatory domain away from the active site of lipase and allows lipase to begin digesting lipids.
Where does lipase come from?
It’s often made in the pancreas, the mouth, and the stomach.
What is the lipid emulsion composed of?
triacylglycerides, cholesterol, cholesterol esters. The clumps are coated with bile acids. Bile salts are ampipathic (have polar and nonpolar domains) and can interact with both environments.
What hormones regulate lipid digestion?
Cholecystokinin (CCK). CCK acts on the gall bladder to secrete bile and on the pancreas to secrete digestive enzymes (like lipase). The acidic chyme causes intestinal cells to secrete secretin, which induces the pancreas to release bicarbonate ion, which increases the pH to tolerable levels and helps lipase/other enzymes operate within their optimal pH.
Where are triacylglycerides digested? Where do their products go? How do they get there?
Triacylglycerides are digested in the liver, but their end products need to be sent all over the body. To get triacylglyceride products into the body (via blood flow), is no simple process. Lipase adds H2O to triacylglyceride and breaks it to form fatty acids and monoglycerols (one fatty acid remaining on the glycerol). These molecules are able to form micelles and sneak across the membrane. Once across the membrane they’re reformed into triacylglycerols. These triacylglycerols are packaged into chylomicrons, which are picked up by lacteals (special fatty acid product packages) and carried off through the blood.
What are the major steps for converting fatty acids to energy?
Triacylglycerols are degraded to fatty acids + glycerol by lipases (in adipose cells). Fatty acids are transported to the liver. Once in the liver, the fatty acids are activated (energy is added) and transported to the mitochondria. In the mitochondria these fatty acids are broken down into acetyl CoA, which is used up in the TCA cycle to produce energy.
How do hormones play a role in fatty acid digestion?
Glucagon and epinephrine both signal fatty acid digestion. Glucagon activity means you’re fasting, so glucagon wants to produce energy from non-glucose sources. Glucagon (or epinephrine) bind to a GPCR. This GPCR phosphorylates the alpha subunit of Gprotein. The alpha subunit activates adenylate cyclase, whch makes cAMP from ATP. cAMP leads to the activation of protein kinase A. Protein kinase A activates perilipin. Perilipin has two functions: restructure fat drops so that triacylglycerides are more accessible for reaction. Perilipin also induces release of cofactor for adipose triglyceride lipase. Adipose triglyceride lipase is used to degrade triacylglycerols
What is the overall structure change in triacylglycerol as it’s digested?
Turned into diacylglycerol by lipase, then turned into monoacylglycerol by lipase. monoacylglycerols + fatty acids can form micelles to travel out of the lumen (interior duct of the gastrointestinal tract) into mucosal cells, where it can be picked up by the lymph + circulatory systems.
What is adipose triglyceride lipase?
The main lipase used to digest triacylglycerides to diacylglyceride to monoacylglycerol. adipose triglyceride lipase is activated by perilipin (perilipin adds a coactivator).
What does perilipin do?
Perilipin is activated by the presence of glucagon or epinephrine (it’s phosphorylated by protein kinase A). Perilipin adds a coactivator to adipose triglyceride lipase which activators the lipase. Perilipin also phosphorylates hormone-sensitive lipase, which converts DAG to MAG
what is chanarin-dorfman syndrome?
A mutation in the coactivator for Adipose triglyceride lipase. AGTL doesn’t bind to the coactivator and isn’t able to break triacylglyceride to diacylglyceride. your liver gets huge because the triacylglyceride stuffs it up, you don’t have energy because you can’t digest fatty acids.
When triacylglycerides are broken down, what happens to the end products?
Glycerol is turned into pyruvate through glycolysis or glucose through gluconeogenesis.
Fatty acids turned into acetyl CoA through fatty acid oxidation and go through the TCA cycle to generate high energy electron carriers.
