Beta Oxidation, Peroxisomes, Ketones

Frage	Antworten
True or false: the net production of ATP from palmitate (16C) through B-oxidation (and then TCA/ETC) is 108.	FALSE. The net production is 106 ATP as two are used in fatty acid oxidation.
In what circumstances are ketone bodies produced?	When a person is in a starvation/fasting state or if they are diabetic.
What is the purpose of fatty acid activation in Beta oxidation?	To join the fatty acid with CoA and transport it to the mitochondrial matrix. This will then allow the Acetyl CoA formed from later steps to power the krebs cycle
Why are ketone bodies produced?	They are produced because oxaloacetate is taken out of mitochondria to be used in gluconeogenesis. Therefore it cannot bind with acetyl CoA for TCA to go ahead. Therefore energy has to be produced in some other way.
Why does oxaloacetate have to be taken out and used in gluconeogenesis? Why can't the acetyl CoA be used directly to make glucose?	Because the link reaction is irreversible therefore the reaction can't occur.
What is the first molecules in beta oxidation?	Acyl CoA
Why is it important that acetyl CoA is broken down in some other way than the TCA?	B-oxidation is inhibited if its products are in low concs. Therefore for it to continue, to allow some production of energy in the body, acetyl CoA has to be broken down.
What enzyme is required to join the fatty acid (Acyl) to CoA?	Acyl CoA synthetase
True or false: the reaction when joiing Acyl to CoA requires ATP?	True. It uses two phosphate groups from ATP to leave AMP + PPi
How is the activation step in B-oxidation made irreversible?	It is irreversible due to rapid hydrolysis of PPi into two individual phosphates.
What kind of reaction is 3-ketothialse (in ketones)?	Thiolysis reaction
How is the fatty acid activation step of B-oxidation regulated?	It is regulated by substrate and hormone concentration. Both cause an increase in the rate of the step.
What is produced from the first reaction in the ketone pathway?	A four carbon molecule from 2 acetyl CoA 2C molecules
Where does the energy come from to drive the first step in the ketone pathway?	Energy is produced from breaking a thioester bond.
How is Acyl CoA transported into the mitochondria?	Using a shuttle.
Why is a shuttle required to transport Acyl CoA into the mitochondria?	Because CoA is a large molecule and therefore it cannot cross the membrane.
What enzyme is responsible for the movement of Acyl CoA across the mitochondrial membrane (in the shuttle)?	Translocase.
What downregulates this first step in beta oxidation?	Malonyl CoA - one of the products of fatty acid synthesis.
What kind of reaction is the first reaction in B-oxidation? (Acyl CoA Dehydrogenase)	It is a redox reaction.
Where does the energy for the first reaction in B-oxidation come from?	The thioester bond of the substrate made in the previous step.
What is the pathway of reactions in beta-oxidation?	Oxidation--> Hydration --> Oxidation --> Lysis
What kind of reaction is the second reaction in B-oxidation (Enoyl CoA Hydratase)? What is the purpose of this step?	It is a hydration reaction (water is added). It is preparation for 2nd oxidation in series.
What kind of reaction is the second step in ketone production (hydroxymethylglutaryl CoA synthase)? What two things are added in this reaction to form a 6C molecule?	it is a condensation. Water and another 2C molecule - acetyl CoA - are added.
What kind of reaction is the third reaction in Beta-oxidation (L-3 hydroxyacyl CoA dehydrogenase)?	Redox reaction - oxidises substrate!! and reduces NAD+
What is the purpose of the second reaction in ketone production?	To destabilise the molecule for the next step.
Where does the energy come from to drive the second reaction (in ketone production)?	Breaking a thioester bond in acetyl CoA
What are two products of the lysis reaction B-ketothiolase?	Acetyl CoA and Acyl CoA
What kind of reaction is the third reaction in ketone production?	An irreversible lyase reaction.
How is the ketone acetoacetate transported out of the cell?	By acetyl transport.
Where does the CoA come from in the last step?	The Krebs Cycle?
Where might the ketone acetoacetate be used in the body for energy?	In tissues such as the brain.
What kind of reaction is the fourth step in ketone production?	It is a redox reaction: the substrate it reduced and NADH is consumed and oxidised to NAD+.
In what circumstance can B-oxidation produce two Acetyl CoA molecules and not an Acyl CoA?	When the Acyl CoA runs through b-oxidation and becomes 4C-ketoacyl CoA.
True or false: the fourth reaction in ketone production is reversible which allows equilibrium between acetate:butyrate to occur depending on the concentration of NAD+/NADH in the mitochondria?	True.
What inhibits the B-ketothiolase reaction?	its product
What other product is formed when B-hydroxybutyrate is produced?	Acetone via a spontaneous irreversible reaction.
What is ketoacidosis?	Ketoacidosis is when acetone is produced via the ketone body pathway and it can be smelt on your breath as it is excreted through the lungs.
Why is a completely separate pathway required for unsaturated fatty acids (other than B-oxidation)?	Because B-oxidation cannot cope with the double bonds.
What are the two types of reactions (and their purpose) that occur in unsaturated fatty acids (and what are the enzymes)?	1 - Isomerisation - to prepare molecule for next step (cis ^3 - enoyl isomerase) 2 - reduction - removes the double bonds (2,4-dienoyl CoA reductase)
Why can odd chain fatty acids not be dealt with by B-oxidation?	Because the end product of the total reaction would be 3C propionyl CoA and NOT acetyl CoA. Prop CoA enters the TCA at succinate.
What is the purpose of producing ketones in the body?	To make sure the important organs and mechanisms of the body still function.
What are the two reactions that are needed to convert 3C propionyl CoA to succinate?	1. Carboxylation requiring ATP to make a 4C molecule 2. Isomerisation requiring VitB12 as enzyme uses it as a cofactor.
What are perioxisomes? What is their function?	Organelles found in cells. They are also able to oxidise fatty acids (but a lot less than B-oxidation in normal conditions).
What is the purpose of reversing the ketone reaction and turning acetoacetate back into acetoacetyl CoA (and eventually acetyl CoA)?	To liberate energy stored in ketones for cells that use them as energy.
What are two of the circumstances which will result in oxidation in perioxisomes and not b-oxidation?	1. when the B-oxidation machinery is damaged 2. when there are very long chain FAs
True or false: the reaction sequence of oxidation in peroxisomes is the same as B-oxidation?	True.
Why are the electrons from FADH2 not passed on to the ETC (in the first step of oxidation in peroxisomes?) What do the electrons produce instead?	Because the reaction occurs outside the mitochondria so the electrons cannot be passed into ETC. Hydrogen peroxide.
Name three cells which may prefer to use ketones as fuel as opposed to glucose.	Renal cortex, heart muscle, brain.
How much of the energy in brain comes from ketones in normal conditions and in starvation?	25% in normal conditions, 75% in starvation.
What happens to glucose and ketone levels as starvation proceeds?	Glucose levels drop and ketone levels rise leading to ketoacidosis.
Why does the brain not use FFA very well to produce energy?	As they do not cross the blood brain barrier very easily.
What is ketosis? Where can it be seen?	Elevated levels of ketone bodies in body. Seen in starving individuals and diabetics.

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Beta Oxidation, Peroxisomes, Ketones

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