Chapter 25: Nitrogen Acquisition and Amino Acid Metabolism

Which of the following is NOT a commonly used transamination pair?

Asp/oxaloacetate

The correct sequence for electron-transport in nitrate reductase is: A. NADH B. -SH C. FAD D. Cyt b557 E. MoCo F. NO3-

A, B, C, D, E, F

Control over nitrogenase activity is accomplished by which of the following?

NH4+ prevents expression of the genes that encode nitrogenase

All of the following are characteristics of phenylketonuria EXCEPT:

air oxidation causes urine to turn dark on standing.

All are characteristics of Maple Syrup Urine Disease EXCEPT:

elevated blood levels of acetoacetate and beta-hydroxybutyrate.

The reaction, glutamate + NAD(P)+ + H2O -> NH4+ + alpha-ketoglutarate + NAD(P)H + H+, is catalyzed by:

glutamate dehydrogenase (GDH).

The reaction, 2 NH4+ + alpha-ketoglutarate + NADPH + ATP -> glutamine + NADP+ + ADP + Pi + H2O, is the combined result of what two enzymes?

glutamate dehydrogenase and glutamine synthetase

All of the carbons and nitrogens of ornithine come biosynthetically from:

glutamate.

Amino acids biosynthesized from aspartate include all EXCEPT:

glutamate.

The carbon skeletons of all of the amino acids below converge to pyruvate EXCEPT:

glutamate.

Animals are totally dependent on plants and microorganisms for nitrogen fixation and nitrate assimilation because animals:

lack the enzymes to reduce N2 and NO3- to NH4+.

Glutamine synthetase (GS) belongs to what class of enzymes?

ligase

Nitrate assimilation occurs in two steps: reduction of nitrate to ____ and further reduction to ____.

nitrite; ammonia

Nitrogen fixation involves the enzyme ____ catalyzing the reaction: N2 + 10___+___ e- -> 2 NH4+ + H2

nitrogenase; H+; 8

Aspartate is formed from transamination of:

oxaloacetate.

Denitrifying bacteria are capable of all EXCEPT:

oxidizing NH4+ to NO3-.

All of the following are true statements regarding the 3-Phosphoglycerate (3-PG) family EXCEPT:

3-PG is diverted from glycolysis by phosphoglycerate mutase.

Nitrite reductase requires ____ electrons to reduce NO2- to NH4+ and the electrons are provided in higher plants through photosynthesis as reduced ____.

6; ferredoxin

What would be a result of a high [Gln]/[alpha-KG] ratio?

An increase in the degree of adenylation of glutamine synthetase.

All are convergent metabolic intermediates of -amino acid carbon skeletons EXCEPT:

Citrate.

Degradation of valine, isoleucine and methionine leads to succinyl-CoA via the sequence of: A. carboxylation using biotin and ATP B. mutase C. methylmalonyl-CoA D. epimerase E. Propionyl-CoA

E, A, C, D, C, B

All of the following are characteristic features of ATP:GS:adenylyl transferase (AT) EXCEPT:

It exists in two forms, PIIA and PIID. PIIA causes the deadenylation of glutamine synthetase and its activity increases with an increase in glutamine.

____ is an intermediate in biosynthesis of ornithine and a regulator of carbamoylphosphate synthetase-I

N-Acetylglutamate

Herbicides (e.g., "Roundup") that inhibit biosynthesis of "essential" amino acids should be relatively safe for animal exposure because animals do not have enzymes of:

Phe, Val, Leu, Ile and His biosynthetic pathways.

All of the following are true of the urea cycle EXCEPT:

Stimulation of carbamoyl-phosphate synthetase I (CPS-I) decreases the activity of the urea cycle.

All of the following are true of transamination EXCEPT:

The coenzyme needed is thiamin pyrophosphate (TPP).

What is nitrogen fixation?

The formation of NH4+ from N2 gas.

What reaction does glutamate dehydrogenase (GDH) catalyze?

The reductive amination of alpha-ketoglutarate to yield glutamate.

In the process of amino acid biosynthesis, how are glutamic acid, glutamine, proline, and arginine all related?

They are all derived from alpha-KG.

Transamination of pyruvate with glutamate as amino donor gives:

alanine.

All N2-fixing systems are nearly identical and have all of the requirements EXCEPT:

all are true.

Elevated levels of homocysteine in the blood is related to all EXCEPT:

all of the above are correct.

In plants and microorganisms, amino acid biosynthesis is a matter of synthesizing the appropriate ____ followed by transamination with ____.

alpha-ketoacid; glutamate

Glutamate synthase (GOGAT) catalyzes the reaction ____+____+ ____-> 2 glutamate + NADP+

alpha-ketoglutarate; NADPH; glutamine

Homoserine and homocysteine are related to serine and cysteine by having:

an additional methylene group.

N-acetylglutamate functions in ammonium incorporation into metabolic intermediates as:

an allosteric activator for carbamoyl-phosphate synthetase I (CPS-I).

Ornithine serves three metabolically important roles, but is not found in proteins. What is one of the important roles of ornithine?

an intermediate in the urea cycle

The involvement of ATP in the nitrogenase complex is because ATP is needed to:

break the N2 triple bond.

The term ketogenic amino acids refers to amino acids:

degraded to yield acetyl CoA or acetoacetate.

All of the following act in feedback inhibition of glutamine synthetase (GS) in prokaryotes EXCEPT:

proline.

All of the following are characteristics of alkaptonuria EXCEPT:

results in mental retardation due to accumulation of Phe metabolites

Bacterial glutamine synthetase (GS) monomers are inactive because they must be:

stacked for interface active site development.

Which of the following directly serves as one of the nitrogen atoms of a urea molecule?

the N of Asp

Nitrifying bacteria obtain their chemical energy from:

the oxidation of NH4+ to NO3-.

Chorismate biosynthesis occurs via the shikimate pathway and is an important precursor in the synthesis of all of the following EXCEPT:

threonine.

Which of the following is an essential amino acid?

valine