Chapter 22: Fat Breakdown and Synthesis Flashcards
Explain the advantages of storing energy as fats as opposed to glycogen
The same amount of calories of fat can be stored without the excess weight. Carbohydrates have to be hydrated so there would be more weight if carbohydrates were used for storing energy.
Explain the “movement” of triacylglycerols across membranes – (break down)
The breakdown of fats starts in the small intestine where it is emulsified by bile salts to make it more h2O soluble. This helps lipases digest the fatty acids which are then absorbed in intestinal cells. And then chylomicrons deliver the fats to tissues. Adipose cells can also release fatty acids that get transported by serum albumin.
Know the possible fates for the glycerol of triacyl glycerol
The glycerol from triglycerides after lipolysis will enter glycolysis or gluconeogenesis through DHAP.
Describe the role of coenzyme A and carnitine in the movement of fatty acids across the
mitochondrial membrane
Coenzyme A is attached to the acetyl group but it cannot cross the mitochondrial membrane. Carnitine will take the place of coenzyme A and take the acetyl group into the mitochondrial membrane. Once there the coenzyme A can reattach and enter the citric acid cycle.
Know the basic steps of beta oxidation (know structures, need not know enzyme names)
- Oxidation
- Hydration
- Oxidation
- Thiolysis
Explain how the cell deals with unsaturated fatty acids in regards to beta oxidation
The double bonds have to be moved around to the second carbon.
What molecules will break down into succinyl CoA and CO2
Propionyl will break down into succinyl CoA. Formyl CoA will break down into CO2.
Know the structures of ketone bodies and their function.
Acetoacetate, beta-hydroxybutyrate and acetone are ketone bodies. They are made when there is excess Acetyl CoA for the liver to use. Function is to feed the brain.
Acetoacetate can undergo nonenzymatic decarboxylation to form acetone which is unwanted. When diabetes goes untreated there are ketone bodies produced since the cells think they are starving so they tell the liver and the liver makes ketone bodies but there may not be enough NADH to convert all the acetoacetate to b-hydroxybutyrate so more acetone is produced. (The acetone can be smelled on their breath).
Explain under what conditions ketone bodies are made.
Ketone Bodies are made under starvation conditions where all the glycogen has been utilized and gluconeogenesis starts to be ran. As this occurs oxaloacetate is produced from pyruvate and the CAC needs oxaloacetate and acetyl CoA so in this time of scarcity the liver will produce ketone bodies to ensure the brain gets nutrients.
Know the reaction catalyzed by the enzyme acetyl CoA carboxylase.
This enzyme is in Fatty Acid Synthesis and is the key control point. The reaction catalyzed is:
Acetyl CoA + CO2–> Malonyl CoA
Fatty acid synthesis uses ACP instead of CoA.
Know the basic steps of fatty acid synthesis (know structures, need not know enzyme
names).
Know how acetyl units are transported out of the mitochondria.
The acetyl CoA units are attached to oxaloacetate to form citrate which has a transporter out of the mitochondria and into the cytosol.
Describe the control of the enzyme acetyl CoA carboxylase.
Hormonal:
-Insulin activates dephosphorylation of Acetyl CoA carboxylase and this activates the enzyme.
Allosteric:
-Citrate stimulates.
-AMP inhibits.
-Palmitate= feedback inhibition
Know that acetyl CoA carboxylase is also controlled at the gene transcription level and
know the dietary factors likely to up-regulate and down-regulate the transcription.
Fasting will cause the levels of Acetyl CoA carboxylase to decrease.
After fasting and then eating lots of carbs, both Acetyl CoA carboxylase and Fatty Acid Synthesis are up-regulated which leads to more mRNA and more protein which makes more enzyme.
