Chapter 18: Nitrogen Metabolism

The fixation of nitrogen (N2) into ammonium (NH4) by nitrogenase requires energy in the form of [x] and [y].

ATP; electrons (ferredoxin)

Nitrogenase utilizes ATP and NADPH to fix [x] into [y].

(di)nitrogen (N2), ammonium (NH4)

The [x] process has enabled fertilization in modern agriculture.

Haber-Bosch

The Haber-Bosch process utilizes [x] and [y] to drive reduction of nitrogen.

Pressure; heat

Legumes such as soybean are grown in part due to their ability to host rhizobia, which [x].

n are grown in part due to their ability to host rhizobia, which [x]. f

[X] is the amino acid immediately formed by direct incorporation of ammonium (NH4+) in mammals.

Gluatamine

Ammonium (NH4+) is assimilated by being directly added to [x].

glutamate

The incorporation of ammonium (NH4) most directly yields the amino acid [x].

glutamine

Together, glutamine synthetase and glutamate synthase enable the incorporation of ammonium into [x], using ATP and [y].

alpha-ketoglutarate, NADPH

Together, glutamine synthetase and glutamate synthase enable the incorporation of ammonium into alpha-ketoglutarate, using [x] and [y].

ATP; NADPH

The source of amino groups for biosynthesis of other amino acids are [x] and [y].

Glutamate; glutamine

Amino groups are swapped between various metabolites to create amino acids by [x] (enzyme).

transaminases

Transaminases utilize a pyridoxal-5-phosphate (PLP) prosthetic (covalently attached co-factor), which forms a [x] with the relevant amino acids.

Schiff base

Transaminases utilize [x] as a prosthetic (covalently attached co-factor) to form Schiff bases with the relevant amino acids.

Pyridoxal-5-phosphate (PLP)

Transamination enables the production of [x] from pyruvate and [y] from oxaloacetate.

alanine, aspartate

The asparagine synthetase differs from the glutamine synthetase in using [x] as the source of the amino group and [y] to drive the reaction.

gluatamine, 2 ~P

Tyrosine is only a non-essential amino acid in mammals because it can be produced by catabolism of [x].

phenylalanine

The metabolic carrier for single/one carbons is [x].

tetrahydrofolate

The biosynthesis of cysteine is always dependent on [x] (amino acid).

serine

What signaling molecules is not derived from an amino acid?

steroids

Match the following signaling molecules to the amino acid from which they were derived. GABA

glutamate

Match the following signaling molecules to the amino acid from which they were derived. Adrenaline

tyrosine

Match the following signaling molecules to the amino acid from which they were derived. Serotonin

tryptophan

Match the following signaling molecules to the amino acid from which they were derived. Dopamine

tyrosine

Match the following signaling molecules to the amino acid from which they were derived. Melatonin

tryptophan

Adrenaline, serotonin and dopamine are signaling molecules derived from [x].

amino acids

Adrenaline and other catecholamines are derived from the amino acid [x].

tyrosine

Tyrosine is the precursor of catecholamine signaling molecules such as [x].

adrenaline

A number of signaling molecules (neurotransmitters &/or hormones) such as [x] are made from a single amino acid

Any one of GABA, gamma-aminobutyrate, adrenaline, epinephrine, noradrenaline, norepinephrine, dopamine, serotonin, melatonin, NO, nitric oxide

Catecholamines such as adrenaline are derived from the amino acid [x].

tyrosine

Cytidine triphosphate (CTP) is biosynthesized by cytosine synthase directly from [x] (abbreviation is fine).

UTP

Biosynthesis of the [x] nucleotides can be described as a linear pathway, with [y] produced directly from [z] (abbreviation is fine).

Pyrimidine, CTP, UTP

Biosynthesis of purines is branched and proceeds through [x] as the last common intermediate.

inosine monophosphate (IMP)

Biosynthesis of purines proceeds through inosine monophosphate, and then [x] afterwards.

branches

Purine nucleotide biosynthesis depends on [x] as a key intermediate, and can be described as being [y].

inosine monophosphate (IMP), branched

The direct source of electrons for nucleotide reduction in DNA biosynthesis is [x], reflecting the formation of a [y] during the reaction.

Thioredoxin, disulfide bond

The electrons required for nucleotide reduction in DNA biosynthesis are shuttled from NADPH through thioredoxin, reflecting the need to reduce [x] back to [y].

a disulfide bond, cysteines

Ribonucleotide reductase catalytic activity requires the [x] reductase.

NADPH:thioredoxin

Transformation of uracil to thymidine requires [x] (carrier).

methylene-tetrahydrofolate

Nucleoside catabolism is initiated by [x], releasing the nitrogenous base and [y].

Phosphorolysis, ribose-1-phosphate

Mammals excrete uric acid (urate) to get rid of nitrogen from

purines

Unlike amino acids and pyrimidines, mammals excrete [x] to get rid of nitrogen from purines.

uric acid (urate)

The nitrogen from which of the following is not secreted as urea by mammals?

purines

Catabolism of [x] and [y] (amino acids) leads to pyruvate.

alanine; cysteine

Catabolism of [x] and [y] (amino acids) leads to oxaloacetate.

asparagine; aspartate

Catabolism of [x] and [y] leads to alpha-ketoglutarate.

glutamine; glutamate

Which of the following does not describe how mammals are able to produce a non-essential amino acid?

cysteine from degradation of methionine, tyrosine from degradation of phenylalanine, arginine from the urea cycle, alanine from transamination of pyruvate

The amino acids [x] and [y] are not essential in humans as they are derived from the catabolism of other amino acids.

Any two of tyrosine, arginine, or cysteine

Which of the following is not an essential amino acid in humans because it can be derived from the urea cycle?

arginine

The amino acid providing most of the free ammonia for the urea cycle is [x]

glutamate

The amino acid providing the second amino group in urea is [x].

asparate

Mammals excrete urea to get rid of nitrogen from which of the following?

amino acids and pyrimidines

In order to get rid of nitrogen muscles export [x] to the liver, where it can be secreted via the urea cycle.

alanine

Excess nitrogen, in the form of carbamoyl phosphate and aspartate are combined in the [x] cycle, for disposal in mammals.

urea

The urea cycle removes excess nitrogen by incorporating the amino groups from [x] and [y].

carbamoyl phosphate; aspartate

The breakdown of pyrimidines results in the production of [x], which enters the urea cycle.

Any one of ammonia, ammonium, NH3, NH4

The ammonium derived from amino acid catabolism enters the [x] in order for the nitrogen to be expelled by mammals.

urea cycle

Arginine is not an essential amino acid in humans because it can be derived from the [x].

urea cycle

Mammals produce arginine via the [x] (pathway).

Mammals produce arginine via the [x] (pathway).