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44 Cards in this Set

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