Lipids 2 Flashcards
Where does the fatty acid metabolism occur?
In the mitochondria (catabolism by B-oxidation, some chain lengthening)
What is the conversion in the oxidative process?
Fatty acid to acetyl CoA to citric acid cycle to energy
What type of process is the acetyl CoA conversion?
Removal of two carbons cycle
Steps of oxidation?
- Activated FA oxidised; introduce a double bond (dehydrogenase enzyme, redox cofactors FAD to FADH2)
- Double bond hydrated (introduces OH group- catalysed by hydratae family enzyme)
- Hydroxyl group oxidised to ketone (dehydrogenase enzyme; redox cofactor NAD reduced to NADH)
- FA cleavage (acetyl CoA and FA that is two carbons shorter, thiolase enzyme, CoA as cofactor)
What in regards to fatty acids mirror each other in chemical reactions?
Fatty acid degradation and synthesis
What are highly concentrated stores of metabolic energy because they’re reduced?
Triacylglycerols
What are lipids ingested as and what must they be degraded to, for absorption across the intestinal epithelium?
Ingested as triacylglycerols, must be degraded to fatty acids
What happens to triacyglycerols in the intestinal lumen?
They’re incorporated into lipid globules composed of bile salts, amphiathic molecules synthesised from cholesterol in the liver and secreted from the gall bladder
What catalyse the hydrolysis of bonds between the fatty acyl group and glycerol of triacylglycerols?
Lipases from the pancreas
What three stages of processing must occur for the utilisation of fatty acids as fuel?
- Lipids must be mobilised; triacylglycerols are degraded to FFAs and glycerol which are released from adipose tissue and transported to the energy-requiring tissues
- At these tissues, the fatty acids must be activated and transported into mitochondria for degradation
- The fatty acids are broken down in a step by step fashion into acetyl CoA, which is then processed in the citric acid cycle
What transports fatty acids and why?
Serum albumin (as not soluble in water)
What is lipolysis?
When triacylglycerols are hydrolysed by hormone-stimulates lipases in adipose tissue
Steps of lipolysis?
- Hormones trigger 7 TM receptors that activate adenylate cyclase
- Increases cyclic AMP stimulates protein kinase A, which phosphorylates triacylglycerol lipase/hormone-sensitive lipase
- Triacylglycerols, by releasing fatty acid from triacylglycerol, forming diacylglycerol- which is converted into a free fatty acid and monoacylglycerol by hormone sensitive lipase
- Monoacylglycerol lipase completes the mobilisation of fatty acids wothvthe production of a free fatty acid and glycerol. Thus, epinephrine and glucagon induce lipolysis
What generates fatty acids and glycerol?
Lipolysis
What must happen to fatty acids for it to be degraded?
Must be activated and transported into mitochondria
What activates a fatty acid for transport?
The formation of a thioester linkage to coenzyme A
What drives the formation of a thioester linkage between the carboxyl group of a fatty acid and the sulphudryl group of CoA?
ATP
Where does the activation of fatty acids occur?
On the outer mitochondrial membranes
What carries a long-chain activated fatty acid into the mitochondrial matrix?
Carnitine
What are fatty acids broken down into and what is it processed in?
Broken down into acetyl CoA and processed in the citric acid cycle
What is the b-oxidation pathway?
Saturated acyl CoA is degraded by a recurring sequence of 4 reactions;
Four steps of B-oxidation?
- Oxidation (FAD)
- Hydration
- Oxidation (NAD+)
- Thiolysis (coenzyme A)
What shortens the fatty acid chain?
Two carbons and acetyl CoA, NADH and FADH2 are generated in each round of fatty acid oxidation
What does the oxidation of FA containing double bonds require?
Additional steps ( as do the oxidation of fatty acids containing an odd number of carbon atoms)
What’s the reaction sequence for the degradation of fatty acids?
Acyl CoA dehydrogenase
Enoyl CoA hydratase
L-3-hydroxyacyl CoA dehydrogenase
B-ketothiolase
What is the oxidation of palmite and how much ATP does it yield?
Palmitoyl CoA + 7FAD+ 7NAD + 7CoA + 7H2O to 8 acetyl CoA + 7FADH2 + 7NADH + 7H
106
When are ketone bodies formed?
From acetyl CoA when fat breakdown predominates
What are a major source of fuel in some tissues?
Ketone bodies (used when starving)
