Biochemistry - Lipid Metabolism Flashcards
What is the definition of a lipid?
Class of organic molecules with low solubility in water and high solubility in nonpolar solvents.
What is an isoprenoid? Name five functions.
Subclass of lipid that includes cholesterol, steroids, and fat-soluble vitamins. Multi-ring structures.
- Bile acids/salts
- Membranes
- Signal molecules
- Cofactors
- Fat soluble vitamins
Name four functions of fatty acids.
- Energy storage
- Membrane formation
- Signaling molecules
- Nerve and thermal insulation
What does the omega number refer to?
The number of carbons from the omega carbon (the last one) to the nearest double bond.
Which carbon on a FA is #1?
The carboxyl carbon
What is particularly important about linoleic and linolenic acid? What disease can result from dietary insufficiency?
They are essential FAs (need to get from diet). Disease includes scaly dermatitis, alopecia (hair loss), thrombocytopenia (low platelet count) and cognitive development (in children).
What is a PUFA?
Polyunsaturated fatty acid
Define medium and long chain FAs.
Medium is 6 to 12 carbons. Long is 14 or longer
At physio pH, are FAs deprotonated? If so, what do they end up forming?
Yeah, they form FA salts with Na+ or K+
How does one name a FA salt compared to FAs?
The “-ic acid” is replaced with “-ate”
How does FA chain length affect solubility.
Inverse proportionality
Why are FA salts soaps?
Amphiphatic properties.
How do double bonds affect melting temp?
Inversely proportional. Note: introduction of the first double bond makes the biggest difference in melting temp (a monounsaturated FA has a MUCH lower melting temp than the corresponding saturated FA)
What types of FAs are readily absorbable in the intestine?
Short and medium chain FAs.
What is the predominant type of dietary fat?
Triacylglycerides (90%)
How does chain length affect FA melting temp?
Directly proportional
What is steatorrhea? Name three potential causes.
Fat in poo.
- Biliary obstruction
- Chronic pancreatic disease that decreases pancreatic lipase
- GI disorders that decrease absorption such as celiac disease.
What are micelles? How do they aid in absorption?
They are FA aggregations that have been made soluble by gall bladder bile salts (emulsifiers). Once the FA concentration reaches a threshold (called the Critical Micelle Concentration), micelles form. As FAs diffuse into intestinal epithelia, more FAs are released from the micelle for absorption.
Where is lipase found? Does it need a cofactor?
It is found in the mouth, stomach, and small intestine. It needs a cofactor to work when in contact with bile salts (called colipase)
Where are bile acids made? From what precursor?
Liver, from cholesterol.
Does peristaltic action promote micelle formation?
Yeah
What is the product of lipase breakdown of TAGs?
Two FAs and one 2-MAG (monoacyl glycerol)
What is a gallstone?
An insoluble cholesterol crystal that forms when bile contains too little soluble salt component
Are bile salts re-used? What is this pathway called? Describe the pathway.
Yes, called the enterohepatic circulation. Bile salts make their way down the intestine and go into the hepatic circulation at the terminal ileum - 95% are recovered.
Once the TAG components are absorbed into intestinal epithelial cells, what happens?
The TAGs are resynthesized.
What is the first step in TAG resynthesis? What enzyme does it?
First step is FA activation with ATP and CoAs-H. Fatty acyl-CoA synthetase does it.
What enzyme is responsible for synthesizing TAGs from the 2-MAG and activated FAs?
Triacylglycerol synthetase.
Where does TAG synthesis occur?
In the ER membrane.
What happens to cholesterol before it can associate with a chylomicron? Why?
Conversion to a cholesterol ester. Cholesterol -OH groups make them too soluble to hang out with TAGs in the chylomicrons.
What enzyme converts cholesterol to cholesterol esters? What does the opposite?
Acyl-coA cholesterol acetyltransferase (ACAT). Cholesterol esterase remakes the cholesterol.
What is Abetalipoproteinemia, aka Bassen-Kornzweig disease?
Defect in MTP. Results in clumsiness and progressive ataxia, neuropathy and vision impairment develop in later childhood or adolescence, low TAG and cholesterol levels, high % of acanthocytes (star-shaped RBCs)
What is the half-life of ingested fatty acids?
~10 minutes
Name the nomenclature for the following FAs: Stearic acid, palmitic acid, myristic acid, oleic acid, linoleic acid, linolenic acid.
Stearic acid: 18:0 Palmitic acid: 16:0 Myristic acid: 14:0 Oleic acid: 18:1 delta9 Linoleic acid: 18:2 delta 9,12 Linolenic acid: 18:3 delta 9,12,15
Which apoprotein binds LDL-R?
B-100
