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59 Cards in this Set
- Front
- Back
What do microorganisms use to reduce N2 to NH3?
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ATP and reduced ferredoxin, a powerful reductant
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What catalyzes the fixation of N2?
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molybdenum-iron cluster in nitrogenase
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Higher organisms consume fixed nitrogen to synthesize what? (3)
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amino acids nucleotides other nitrogen-containing biomolecules |
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What does ammonia exist as in aqueous solutions? |
(NH4)+
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What are the major points of entry of (NH4)+ into metabolism? |
glutamine or glutamate
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How many amino acids can human begins synthesize? |
11/20
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True or false: the pathways for the synthesis of nonessential amino acids are quite simple. |
true
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What catalyzes the reductive amination of alpha-ketoglutarate to glutamate? |
glutamate dehydrogenase
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What takes place in the synthesis of most amino acids?
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transamination reaction
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What is synthesized by the transamination of pyruvate? |
alanine
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What is synthesized by the transamination of oxaloacetate? |
aspartate
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What is tetrahydrofolate?
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carrier of activated one-carbon units
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carries one-carbon units at three oxidation states, which are interconvertible |
tetrahydrofolate
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What is the major donor of activated methyl groups? |
SAM
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How is SAM synthesized? |
by the transfer of an adenosyl group from ATP to the sulfur atom of methionine
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What is formed when an activated methyl group from SAM is transferred to an acceptor? |
S-adenosylhomocysteine
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What happens to S-adenosylhomocysteine? |
hydrolyzed to adenosine and homocysteine
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What happens to homocysteine?
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methylated to methionine to complete the activated methyl cycle
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What are most of the pathways of amino acid biosynthesis regulated by? |
feedback inhibition
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What is feedback inhibition? |
Committed step is allosterically inhibited by the final product. |
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requires extensive interaction and includes both negative and positive regulation |
regulation of branched pathways
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series of reactions in which groups from methionine are converted into a biochemically reactive form through the formation of SAM |
activated methyl cycle
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What is SAM? |
S-adenosylmethionine
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What can an active methyl group be transferred from SAM to? |
acceptor molecules such as norepinephrine
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What can methionine be regenerated from in the activated methyl cycle? |
homocysteine and N5-methyltetrahydrofolate
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What is the committed step?
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first irreversible step in a metabolic pathway under physiological conditions
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What is the committed step catalyzed by? |
allosteric enzyme
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regulatory strategy in which the enzyme catalyzing the committed step common to several pathways is incrementally inhibited by the products of each of the pathways |
cumulative feedback inhibition
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regulatory strategy in which the committed step common to several pathways is catalyzed by different enzymes with the same catalytic properties but different regulatory properties |
enzyme multiplicity
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each enzyme responds to the final product of one of the pathways having the committed step in common |
enzyme multiplicity
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What is nitrogen fixation? |
conversion of nitrogen gas (N2) into ammonia
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What is the first step in the flow of nitrogen into amino acids, nucleotides, and other nitrogen-containing compounds in organisms? |
nitrogen fixation
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catalyzes the reduction of diatomic nitrogen to ammonia |
nitrogenase complex
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What is nitrogenase complex found in? |
bacteria and the blue-green algae
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prosthetic group that plays a key role in transamination reactions |
pyridoxal phosphate (PLP)
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What is PLP? |
pyridoxal phosphate
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What is PLP derived from? |
vitamin B6
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Trace the flow of nitrogen from atmospheric N2 to glutamine. |
N2 -nitrogenase complex> NH3/(NH4)+ -glutamate dehydrogenase> glutamate -glutamine synthetase> glutamine
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What amino acids are derived from oxaloacetate?
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MTKIND
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What amino acids are derived from phosphoenolpyruvate and erythrose 4-phosphate? |
WFY
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What amino acids are derived from pyruvate? |
AVL
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What amino acids are derived from ribose 5-phosphate? |
H
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What amino acids are derived from alpha-ketoglutarate? |
QPER
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What amino acids are derived from 3-phosphoglycerate? |
GCS
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What organisms are capable of nitrogen fixation?
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diazotrophic
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What is methylated to form methionine?
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homocysteine
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What conenzyme is required by aminotransferases? |
pyridoxal phosphate
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What is responsible for nitrogen fixation? |
nitrogenase complex
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What is a common amino acid donor? |
glutamate
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True or false: the mechanistic complexity of nitrogenase is necessary because nitrogen fixation is a thermodynamically unfavorable process. |
false, favorable but the reaction is not kinetically possible without ATP (high activation energy)
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Nitrogen-fixing bacteria on the roots of some plants can consume as much as 20% of the ATP produced by the plant—consumption that does not seem very beneficial to the plant. Explain why plants tolerate this loss of valuable resources and what the bacteria are doing with the ATP. |
The bacteria provide the plant with ammonia by reducing atmospheric nitrogen.
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What are the seven precursors of the 20 amino acids? |
oxaloacetate pyruvate ribose-5-phosphate phosphoenolpyruvate erthrose-4-phosphate alpha-ketoglutarate 3-phosphoglycerate |
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If an animal is fed N15-labeled aspartate, many amino acids bearing the N15 label subsequently appear. What reactions take part in the transfer of the label? |
A reversible transamination reaction will transfer the labeled amino group from aspartate to alpha-ketoglutarate to form glutamate and oxaloacetate. Glutamate is an amino-group donor for the synthesis of many amino acids from their corresponding ketoacids.
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Differentiate between SAM and tetrahydrofolate. |
Both carry one-carbon units. SAM is a more useful methyl donor than tetrahydrofolate because it has a greater transfer potential.
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Which of the 20 amino acids can be synthesized directly from a common metabolic intermediate by a transamination reaction? |
DEA
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Propose a scheme of sequential feedback inhibition that would result in the production of equal amounts of Y and Z for the following pathway: A -> B -> C that splits into D->E->Y and F->G->Z. |
Y could inhibit the C->D step, Z could inhibit the C->F step, and C could inhibit A->B. |
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Propose a scheme of concerted feedback inhibition that would result in the production of equal amounts of Y and Z for the following pathway: A -> B -> C that splits into D->E->Y and F->G->Z. |
Y could inhibit the C->D step, Z could inhibit the C->F step, and the A->B step could be inhibited only in the presence of both Y and Z.
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We have identified three biomolecules that carry activated one-carbon units of some sort. Name these three carriers. |
tetrahydrofolate SAM biotin |
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A person on a diet lacking in methionine would not be able to synthesize adequate amounts of proteins. However, insufficient protein synthesis would not be the only biochemical problem such a person would face. What other biosynthesis would be affected by a lack of dietary methionine? |
Methionine is a component of SAM, which is a methyl donor for the synthesis of phosphatidylcholine from phosphatidylethanolamine.
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