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The Tricarboxylic Acid Cycle and the Electron Transport Chain

Terms in this set (41)

What is the importance of ATP?
Importance of ATP: if the heart were not able to regenerate ATP, all of its ATP would be depleted in less than 1 minute

Each heartbeat uses about 2% of the heart's ATP
Why must the heart use oxidative phosphorylation to produce ATP?
The heart must use oxidative phosphorylation to produce enough ATP, which is why a lack of oxygen due to a blockage in a coronary artery is so problematic
How much ATP is produced by anaerobic glycolysis?
Much less ATP is produced by anaerobic glycolysis (which occurs in the CYTOSOL)
What do tissues with low O2 and few or no mitochondria use?
Tissues with low oxygen or few or no mitochondria (RED BLOOD CELLS) must use this method of energy generation
What pathway can hypoxic tissues use?
Hypoxic tissues can use this pathway as well, over the short-term until oxygen delivery is restored, which is why lactate in the blood is used as an indicator of tissue perfusion
What can all the different macronutrients be metabolized to?
All of the different macronutrients can be metabolized to acetyl CoA
What is acetyl CoA a substrate for?
Acetyl CoA is the substrate for the tricarboxylic acid cycle (TCA)
What are oxygen requirements?
We must have oxygen to efficiently provide energy

Anything that interferes with delivery or utilization of oxygen threatens life
What is tissue hypoxia a result of?
Tissue hypoxia results in cell deaths in that area, anoxia is total lack of oxygen (suffocation) and chemicals such as cyanide can block utilization of oxygen, prevent energy generation and shut cells down (kill them)
Difference between aerobic vs aerobic respiration?
Similarties= both produce ATP

Differences= aerobic requires 02, occurs in mitochondria and produces up to 36 ATP and anaerobic does not require )2 and occurs in cytoplasm and produces 2ATP
What are mitochondria?
Mitochondria are known as the "powerhouse" of the cell because of their function in energy generation
What is mitochondria the cite of?
This is the site of the TCA cycle and the electron transport chain
Inner vs outer membrane of mitochondria?
There is an outer and inner membrane, the outer is permeable to small ions, but the inner membrane is impermeable so that the hydrogen ion gradient can be maintained to drive the synthesis of ATP
What can the oxidation of all different fuels generate?
The oxidation of all of the different fuels can generate acetyl coenzyme A (acetyl CoA), the 2-carbon substrate for the tricarboxylic acid cycle (TCA cycle)
What is the TCA cycle also known as? Where does it occur?
The TCA cycle is also known as the Kreb's cycle and the citric acid cycle (CAC) and it occurs in MITOCHONDRIA
What do the 2 carbons from acetyl CoA combine with?
The 2 carbons from acetyl CoA combine with 4 more in the cycle (oxaloacetate) to make the 6-carbon citric acid - because it is a cycle, the original 2 carbons are oxidized to CO2 and the 4-carbon oxaloacetate is regenerated
What is the link between tricarboxylic acid cycle and glycolysis?
The link between the tricarboxylic acid cycle and glycolysis (glucose metabolism in the CYTOSOL) is the pyruvate dehydrogenase enzyme complex (PDC)
What does PDC convert?
The PDC converts the two 3-carbon pyruvate molecules generated from one molecule of glucose (a 6-carbon molecule) by glycolysis to the 2-carbon acetyl CoA - OXYGEN is the "ticket" for entry into the TCA cycle to generate ATP much more efficiently
What do oxidations and reduction reactions do?
Oxidations and reductions are the reactions that drive energy generation

To remember which is which "LEO the lion says GER". Loss of Electrons = Oxidation and Gain of Electrons = Reduction
What are reduced in the TCA cycle?
NAD+ and FAD are reduced in the TCA cycle and then regenerated by oxidation in the electron transport chain
What is the electron transport chain also known as?
oxidative phosphorylation
Slide 15 + 16
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pyruvate dehydrogenase complex
Without the ability to convert pyruvate to acetyl CoA, this product of glucose metabolism cannot enter the tricarboxylic acid cycle

If pyruvate cannot be converted to acetyl CoA, it is reduced to lactate

Lactate can build up and H+ are generated via the hydrolysis of the ATP generated and the pH of the blood and then drop, causing acidosis
What is mitochondrial DNA only passed from?
Mitochondrial DNA is passed on only from a maternal source
What are diseases called OXPHOS caused by?
There are a series of diseases called OXPHOS that involve mutations in DNA that codes for mitochondrial proteins
What do ragged red fibres result from?
"Ragged red fibres" result from clumps of diseased mitochondria aggregating in muscle tissue
What tissues are most affected?
Because the central nervous system and muscle have the highest ATP requirements, these tissues are the most affected
What is the most common cause in mitochondrial tRNA?
In MERRF the most common cause is a point mutation in the mitochondrial tRNALys

MERRF=Myoclonic Epilepsy with Ragged Red Fibres
What is glycolysis?
One of the principal pathways for energy generation in cells

This process is present in all cell types

This pathway can function in energy generation with and without oxygen
How is ATP produced during glycolysis?
ATP is produced during glycolysis by "substrate-level" phosphorylation; the phosphate is transferred to AD P from a high-energy intermediate
What is the product of glycolysis?
The product of glycolysis, pyruvate, can then go on to produce more ATP through oxidative phosphorylation
In the absence of oxygen, pyruvate can be converted to what?
In the absence of oxygen pyruvate can be converted to lactate; NADH can be oxidized back to NAD+ by lactate dehydrogenase to participate in further energy generation
What do the oxidation-reduction reactions use? Where?
The oxidation-reduction reactions to regenerate electron transferring molecules in the mitochondria use oxygen
What does an anaerobic pathway lack?
The anaerobic pathway lacks oxygen, so would shut down unless NADH could be oxidized back to NAD+ - this is accomplished by reducing pyruvate to lactate
What do certain tissues lack?
Certain tissues lack mitochondria since it might interfere with their function
What do RBCs retain their function from?
Because of their function in oxygen transport, red blood cells obtain their energy from anaerobic glycolysis (they lack mitochondria)
What do the tissues in the eye need?
The tissues in the eye need to be free from light-deflecting structures such as mitochondria and obtain most of their energy this way as well
Slide 26
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Metabolic acidosis
Anaerobic metabolism (glycolysis) is often associated with "lactic acidosis" - this is misnomer as lactic acid is never generated (pyruvate to lactate, no lactic acid)

Metabolic acidosis may or may not occur when lactate levels are increased due to mitochondrial dysfunction

Important to note that the H+ that cause this are not generated from the dissociation of lactic acid to lactate

Use of ATP (hydrolysis) results in the generation of H+ (and ADP)

This may be important clinically because then anion gaps cannot be explained by an increase in lactate
Fatty acid oxidation
Fatty acids are stored in the body as triglycerides, an efficient and lightweight method of energy storage

Because fatty acids are more reduced than carbohydrates they provide more energy (glucose is already partially oxidized)
B- Oxidation
β-oxidation of fatty acids is the process which occurs with long chain fatty acids (C12-C20), the most common component of our diets

Long-chain fatty acids are insoluble and when released from adipose tissue must be transported through blood bound to albumin

Fatty acids are the main source of energy during fasting, but not all tissues can use this fuel

It is called β-oxidation because it is the bond between the α and βcarbon that is broken in successive rounds to create 2-carbon acetyl CoA molecules that can enter the TCA cycle

Fatty acids enter this process (in the mitochondria) if they are long-chain and have an even number of carbons
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