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44 Cards in this Set
- Front
- Back
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What are reduction potentials a measurement of?
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They are a measurement of electron affinity
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What do coenzymes provide?
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They provide reactive groups that function in enzyme catalysis
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What is the pyruvate dehydrogenase complex?
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It is a metabolic machine
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What is Thiamin also known as, and what does it do?
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It is also known as vitamin B, and it is an important enzyme cofactor required for a variety of metabolic reactions.
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What is Berberi?
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It is a disease caused by thiamin deficiency resulting in severe weight loss and neurological symptoms
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What are some examples of foods rich in thiamin?
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Watermelon, sunflower seeds, black beans, and thiamin enriched grains and breads
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What are redox reactions?
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They represent a form of energy conversion involving the transfer of electron pairs from organic substrates to the carrier molecules NAD+ and FAD
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What is the energy available from redox reactions due to?
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It is due to the differences in the electron affinity of two compounds
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What do couples redox reactions consist of?
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They consist of two half reactions
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What are the two half reactions of redox reactions?
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The first is an oxidation reaction (loss of electrons). The second is a reduction reaction (gain of electrons)
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What are compounds called that accept electrons?
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They are called oxidants
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What are compounds called that donate electrons?
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They are called reductants
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What are redox reactions characterized by?
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They are characterized by a loss and gain of electrons from carbon
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Each half reaction consists of what?
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A conjugate redox pair
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What is it useful to think of glucose as?
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It is useful to think of glucose as a biochemical battery
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The reduction of NAD+ to NADH involves the transfer of what?
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A hydride ion (:H-)
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What does a hydride ion contain?
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It contains 2 e- and 1 H+
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FADH is reduced by sequential addition of what?
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One hydrogen (1 e- and 1 H+) at a time
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How is the amount of energy available from a coupled redox reaction defined?
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It is defined as being directly related to the difference between two reduction potentials and is defined by the term DeltaEo'
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How do you find DeltaEo'?
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It is equal to (Eo'[e- acceptor]) - (Eo'[e- donor])
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How is deltaEo' related to the change in free energy?
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DeltaGo' = -nF(deltaEo')
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If you have a positive DeltaEo', will the reaction be favorable or unfavorable?
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If DeltaEo' is positive, you will have a favorable reaction because DeltaGo' will be negative
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For a coupled redox reaction to be favorable, the reduction potential of the electron acceptor needs to be more or less positive than the electron donor?
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It needs to be more positive
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What happens to pyruvate that is destined for the citrate cycle (or fatty acid synthesis)?
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It is converted to acetyl CoA by the enzyme pyruvate dehydrogenase
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What are the two fates of acetyl-CoA in the cell?
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It can be metabolized by the citrate cycle to convert redox energy to ATP by oxidative phosphorylation. It can be used as a form of stored energy by conversion to fatty acids that are transported to adipocytes (fat cells) as triglycerides
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What does the pyruvate dehydrogenase complex?
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It catalyzes the oxidative decarboxylation of pyruvate to form CO2 and acetyl-CoA
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How does it accomplish this?
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It uses a five step mechanism that requires three distinct enzymes and five difference coenzymes
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What is NAD+ and where does it come from?
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It is nicotinamide adenine dinucleotide, and it is derived from the water-solube vitamin niacin, which is also called vitamin B3.
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What does severe niacin difficiency cause?
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It causes pellagra
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Why is pellagra rare in Mexico?
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It is rare in Mexico because corn used or tortillas is traditionally soaked in lime solution (calcium oxide) prior to cooking and this releases niacin from its bound form upon heating
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What is FAD and where does it come from?
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It is flavin adenine dinucleotide and it is derived from the water-soluble vitamin riboflavin, which is also called vitamin B2.
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What is CoA and where does it come from?
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It is Coenzyme A and it is derived from the water-solube vitamin pantothenic acid, which is also called vitamin B5.
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Why is CoA absolutely essential for life?
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It is required for energy conversion by the citrate cycle, it is also a cofactor in fatty acid, acetylcholine, heme, and cholesterol biosynthetic pathways
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What is TPP and where does it come from?
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It is thiamin pyrophosphate and it is derived from the water-solube vitamin thiamin (or thiamine) which is also called vitamin B1
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Why do those people who eat foods rich in the enzyme thiaminase get thiamine deficiency?
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Thiaminase degrades thiamin during digestion
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What contains thiaminase?
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Raw fish contains thiaminase, as does African silkworms, which are a favorite food in some Nigerian cultures
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What is lipoamide and what is its role?
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It is alpha-Lipoic acid and it its role in metabolic reactions is to provide a reactive disulfide that can participate in redox reactions within the enzyme active site
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What is the reaction for converting pyruvate to acetyl-CoA?
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Pyruvate + CoA + NAD+ --> acetyl-CoA + CO2 + NADH
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Is this reaction favorable?
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It is very favorable (DeltaGo' = -33.4 kJ/mol
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What is a naturally ocuring inhibitor of lipoamide coenzyme function?
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The element arsenic (As), which in the form of arsenite (AsO3^3-) creates bidentate adducts on dihydrolipoamide
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What can inadvertant ingestion of arsenite lead to?
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An untimely death
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How?
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It irreversibly blocks the catalytic activity of lipoamide-containing enzymes such as the pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase complexes
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What does the reduction potential (DeltaE) for a coupled reaction represent?
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It represents the tendency of the reductant in one conjugate redox pair to donate electrons to the oxidant of the other conjugate redox pair
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What are coenzymes and how do they function in the pyruvate dehydrogenase reaction?
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They are biomolecules that provide additional functional groups to enzyme active sites and participate in catalytic mechanisms
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