Krebs Cycle

Question	Answer
What are other names for the Krebs cycle?	Citric Acid Cycle, TCA cycle
Where does the majority of ATP production occur?	In the mitochondria of the cell
What is required for mitochondrial function?	An abundance of oxygen
How does the Krebs cycle generally work?	Acetyl-CoA enters the citric acid cycle, CO2 and electrons are released (which go into the ETC)
What happens in Stage I of generation of ATP from food?	Fats, polysaccharides, proteins are broken down into their monomers (fatty acids and glycerol, glucose and other sugars, amino acids)
What happens in Stage II of generation of food from ATP?	Carbons from the molecules broken down in Stage I are incorporated into Coenzyme-A to produce Acetyl-CoA
What happens in Stage III of generation of ATP from foods?	AcetylCoA enters the citric acid cycle, electrons enter the ETC which is linked to oxidative phosphorylation and ATP is produced
Under aerobic conditions, what happens to glucose in glycolysis?	Glucose is converted into Pyruvate and then pyruvate is converted to AcetylCoA
Under anaerobic conditions, what happens to glucose in glycolysis?	Glucose is converted to pyruvate and pyruvate is then converted to lactate
Why do you need lots of oxygen in the stages of generation of ATP from foods?	Because oxygen acts as the electron acceptor (acid) and H20 is produced
What stage of generation of ATP from foods is most of the energy produced in?	Stage III
What is produced from the conversion of pyruvate to acetylCoA	Co2, 2 electrons
What are the main products produced from the citric acid cycle?	GTP (or ATP), 8 electrons, 2 CO2
Where does the citric acid cycle take place?	It takes place in the mitochondrial matrix
How does the citric acid cycle commence?	Commences with the condensation of AcetylCoA with oxaloacetate to form citrate
Why in the inner mitochondrial membrane invaginated?	Invaginations increase the surface area of the membrane
What is the basic structure of the mitochondria?	Outer mitochondrial membrane, inner mitochondrial membrane, matrix
What is the purpose of the outer mitochondrial membrane?	It holds the whole structure together, freely permeable
What is the purpose of the inner mitochondrial membrane?	It is a semi permeable membrane that selectively transports proteins across, pH and charge gradient set up along this membrane, hydrophilic molecules cannot freely cross
What part of the molecule from acetylCoA enters the citric acid cycle?	The acetyl unit that came from pyruvate
How is the TCA controlled?	Adjusted to meet the cell's need for ATP - when ATP is low the rate of cycle is increased, when ATP is high the rate of cycle is decreased, allosteric interactions also control the cycle
Describe the 4 control points of the TCA	ATP, AcetylcoA and NADH can inhibit the conversion of Pyruvate to Acetyl CoA ATP and NADH can inhibit the conversion of Isocitrate to a-ketoglutarate ATP, succinylCoA and NADH can inhibit a-ketoglutarate from forming SuccinylCoA ADP can stimulate isocitrate to form a-ketoglutarate
Other than energy, what else does the TCA also provide?	It provides intermediate molecules for biosynthesis of molecules in other pathways
How many NADH are produced in the TCA?	3 NADH
How many FADH are produced in TCA?	1 FADH
How many GTP/ATP are produced in TCA?	1 GTP/ATP
What happens to NADH and FADH if oxygen is abundant?	They enter the the ETC which generates a proton gradient that drives oxidative phosphorylation (ATP synthesis)
What is oxidative phosphorylation?	The synthesis of ATP
From each pair of electrons from NADH, how many ATP molecules are generated?	2.5 ATP for every NADH
From each pair of electrons from FADH, how many ATP molecules are generated?	1.5 ATP for every FADH
Why does NADH produce more ATP than FADH?	Because FADH enters the ETC later than NADH
In one turn of the citric acid cycle, how many ATP are produced?	1 ATP

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	Created by Olivia Hocking over 11 years ago