Deck 14: Nitrogen Metabolism I: Synthesis

Question 1

The glutamate family of amino acids includes all of the following except _____.

A) Glutamine
B) Arginine
C) Lysine
D) Proline
E) None of the above is correct

Answer 1

C

Question 2

Which of the following is an example of an excitatory neurotransmitter?

A) Serotonin
B) Glycine
C) Glutamine
D) Glutamate
E) None of the above is correct

Answer 2

D

Question 3

All of the following are referred to collectively as the branched chain amino acids except _________.

A) Valine
B) Glycine
C) Leucine
D) Isoleucine
E) None of the above is correct

Answer 3

B

Question 4

Which of the following is an example of an inhibitory neurotransmitter?

A) Glycine
B) $\gamma$ -Aminobutyrate
C) Glutamate
D) Both A and B are correct
E) All of the above are correct

Question 5

Glycine is used as a precursor molecule in the synthesis of all of the following except _______.

A) Glutathione
B) Heme
C) Purine bases
D) Chlorophyll
E) Carnitine

Question 6

In plants fixed nitrogen is assimilated into __________.

A) Serine
B) Glutathione
C) Lysine
D) Threonine
E) Glutamine

Question 7

$\alpha$ -Ketoisovalerate is an intermediate formed during the synthesis of _________.

A) Leucine
B) Lysine
C) Threonine
D) Both A and B are correct
E) Both A and C are correct

Question 8

The group of molecules called the catecholamines include all of the following except _________.

A) Histamine
B) Epinephrine
C) Dopamine
D) Norepinephrine
E) Both A and C are correct

Question 9

Tryptophan is a precursor in the synthesis of _________.

A) Carnitine
B) NAD
C) GABA
D) Both A and B are correct
E) All of the above are correct

Question 10

Chorismate is a precursor in the synthesis of all of the following except _______.

A) Phenylalanine
B) Tryptophan
C) Ubiquinone
D) Tyrosine
E) Guanidoacetate

Question 11

Molecules involved in histidine synthesis include ________.

A) Phosphoribosylpyrophosphate
B) ATP
C) Glutamate
D) Both A and C are correct
E) All of the above are correct

Question 12

All of the following statements concerning folic acid are true except:

A) N⁵,N¹⁰-methylene THF is a product of the cleavage of glycine.
B) Vitamin B₁₂ is required for the N⁵-methyl THF-dependent conversion of homocysteine to methionine.
C) N¹⁰-formyl THF, CO₂, and aspartate are precursors in the synthesis of hypoxanthine
D) Folic acid is a B vitamin.
E) Folic acid requires intrinsic factor for its absorption in the intestine.

Question 13

SAM is a methyl donor in the synthesis of ______.

A) Methionine
B) Creatine
C) Phosphatidylcholine
D) Both A and C are correct
E) All of the above are correct

Question 14

Amethopterin is a structural analogue of _________.

A) Thiamine
B) GABA
C) Folate
D) MPPP
E) Mercapturic acid

Question 15

The transport of GSH out of cells serves all of the following functions except ______.

A) Protection of the plasma membrane
B) Amino acid transport
C) Transfer of sulfur atoms out of cells
D) Formation of mercapturic acid derivatives of organic contaminants
E) None of the above is correct

Question 16

All of the following are purine bases except _____.

A) Guanine
B) Thymine
C) Adenine
D) Hypoxanthine
E) All of the above are purine bases

Question 17

Deficiency of _______ causes Lesch-Nyhan syndrome.

A) Folic acid
B) Carbamoyl phosphate synthetase II
C) UMP synthase
D) HGPRT
E) Mg-Protoporphyrin methylesterase

Question 18

All of the following are directly involved in the synthesis of deoxyribonucleic acid except _______.

A) Thioredoxin
B) NADPH
C) Ribonucleotide reductase
D) Thioredoxin reductase
E) HGPRT

Question 19

Inorganic nitrogen is initially assimilated into which of the following amino acids

A) Glycine
B) Alanine
C) Serine
D) Glutamine
E) Leucine

Question 20

The amino acids serine and _______ are preferentially used to synthesize glucose for export from the liver

A) Lysine
B) Histidine
C) Alanine
D) Tryptophan
E) Glycine

Question 21

Nitrogen fixation requires iron and ________ as cofactors.

A) Cu
B) Zn
C) Mo
D) Ba
E) Mg

Question 22

One-carbon carriers in metabolism include

A) Biotin
B) Folate
C) SAM
D) Both B and C are correct
E) All of the above are correct

Question 23

Which of the following is an $\alpha$ -keto acid/ $\alpha$ -amino acid pair used in transamination?

A) Pyruvate/leucine
B) Oxaloacetate/aspartate
C) Oxaloacetate/glutamate
D) $\alpha$ -Ketoglutarate/aspartate
E) $\alpha$ -Keto- $\beta$ -hydroxybutyrate/phenylalanine

Question 24

In plants the pathway by which most ammonium ion is incorporated into organic molecules requires

A) Glutamate synthetase
B) Glutamine synthetase
C) Reduced ferredoxin or NADPH
D) Both B and C are correct
E) All of the above are correct

Question 25

Asparagine is formed from aspartic acid and _________ .

A) SAM
B) Glutamine
C) Ammonium ions
D) Both A and C are correct
E) All of the above are correct

Question 26

The benzene ring of the aromatic amino acids is formed by the

A) Dehydrogenation of cyclohexane
B) Deamination of dietary phenylalanine
C) Shikimate pathway
D) Dehydroxylation of tyrosine
E) Transamination of $\alpha$ -keto- $\beta$ -methylvalerate

Question 27

The oxidation state of the methenyl group (-CH=) is comparable to that of ____.

A) Methanol
B) Formaldehyde
C) Formate
D) Both A and B are correct
E) All of the above are correct

Question 28

The methylated product of _______ is creatine.

A) Norepinephrine
B) $\gamma$ -Aminobutyric acid
C) Guanidinoacetate
D) Phosphoribosylglycinamide
E) Hemin

Question 29

The fixation of nitrogen requires _______.

A) Fe-Mo protein
B) Fe protein
C) Ferredoxin
D) Both A and B are correct
E) All of the above are correct

Question 30

Most aminotransferases utilize ________as the recipient $\alpha$ -keto acid.

A) $\alpha$ -Ketoglutarate
B) Pyruvate
C) Oxaloacetate
D) Phenylpyruvate
E) Imidazolpyruvate

Question 31

The primary energy source for enterocytes is:

A) Glucose
B) Fatty acids
C) Glutamine
D) Lysine
E) Alanine

Question 32

________ ATP molecules are required to convert one mole of nitrogen to two ammonia molecules.

A) 1
B) 5
C) 8
D) 16
E) 20

Question 33

The first step in nitrogen fixation is ________.

A) Binding of nitrogen to the Fe-S complex
B) Binding of nitrogen to the Mo-Fe complex
C) Transfer of electrons to ferredoxin from NADPH
D) Conversion of nitrogen to H-N=N-H
E) Conversion of nitrogen to hydrazine

Question 34

The major form of regulation of nitrogen fixation is _______.

A) ATP levels
B) NADPH levels
C) Transcriptional control of the nitrogen fixation genes
D) Ammonia levels
E) Nitrogen availability

Question 35

The first amino acid containing newly fixed nitrogen is _______.

A) Glutamine
B) Glycine
C) Proline
D) Asparagine
E) Alanine

Question 36

Which of the following is not a gasotransmitter?

A) NO
B) CO₂
C) CO
D) H₂S
E) Both A and D are correct

Question 37

Which of the following compounds is not present in the normal process of nitrogen fixation

A) Elemental nitrogen
B) HN=NH
C) NH₂OH
D) H₂NNH₂
E) None of the above

Question 38

Hydrogen sulfide is produced from

A) SAM
B) Cysteine
C) Cystine
D) Both B and C are correct
E) All of the above are correct

Question 39

The six families of amino acids are glutamate, aromatic, serine, aspartate, pyruvate, and _______.

A) Glycine
B) Histidine
C) Tyrosine
D) Tryptophan
E) Ketogenic

Question 40

Which of the following neurotransmitters are derived from amino acids?

A) Histamine
B) NADH
C) Catecholamines
D) SAM
E) Both A and C are correct

Question 41

In ocean water phytoplankton growth is limited by temperature and low levels of nutrients containing

A) Sodium
B) Carbon dioxide
C) Nitrogen
D) Potassium
E) Calcium

Question 42

Hypoxic water is characterized by

A) High levels of ammonia
B) Low levels of oxygen
C) High levels of oxygen
D) Excessive warmth
E) Excessive nutrients

Question 43

The ultimate products of mineralization of organic nitrogen is

A) Ammonia
B) Nitrate
C) Nitrite
D) Dinitrogen
E) Amino acids

Question 44

The most common intracellular reducing agent is

A) NADP
B) NADPH
C) Ammonia
D) Glutathione
E) Cysteine

Question 45

In nitrogen fixation by microorganisms what gas other than ammonia is produced?

A) Hydrazine
B) Carbon dioxide
C) Water vapor
D) Hydrogen
E) Oxygen

Question 46

Which of the following is not a function of glutathione

A) Antioxidant
B) Cofactor for antioxidant enzymes
C) Protect cells from xenobiotics
D) Maintain sulfhydryl groups in reduced form
E) Provides reducing equivalents for nitrogen fixation

Question 47

What is meant by the term amino acid pool?

Question 48

What is a retrograde neurotransmitter?

Question 49

What is meant by the term one-carbon metabolism?

Question 50

The concentration of serine differs significantly in blood flowing from the liver to the rest of the body and the nutrients entering the enterocyte. Explain why the concentrations change.

Question 51

Why are nitrogen compounds limited in the biosphere? Give two reasons.

Question 52

The concentration of alanine differs significantly in blood flowing from the liver to the rest of the body and the nutrients entering the enterocyte. Explain why the concentrations change.

Question 53

Why are transamination reactions important in both the synthesis and degradation of amino acids?

Question 54

What are the two major classes of neurotransmitters in terms of their effects on postsynaptic cells? How do their modes of action differ? Give examples of each type of neurotransmitter.

Question 55

List the major reactions in the synthesis of arginine from glutamate.

Question 56

Illustrate the pathway to synthesize glycine.

Question 57

What are the most important carriers in one-carbon metabolism? Give two examples of processes in which each one participates.

Question 58

Glutathione is an important intracellular thiol. List five functions of glutathione in the body.

Question 59

Discuss the roles of branched-chain amino acids (BCAAs) in protein structure and synthesis.

Question 60

Through what intermediates do nitrogen atoms pass during its reduction by nitrogenase?

Question 61

Tetrahydrofolate, a biologically active form of folic acid is shown below. How is it formed?
Folic Acid

Question 62

Identify the following molecule. What is its metabolic role?

Question 63

What carbon in uracil is derived from carbon dioxide?

Question 64

In the nitrogen reductase system for every molecule of ammonia released one molecule of hydrogen gas is also produced. What is the source of the hydrogen gas?

Question 65

Nitrogenase complexes are irreversibly inactivated by oxygen. Explain how the nitrogen-fixing bacteria solve this problem.

Question 66

In pyrimidine nucleosides the anti conformation predominates because of steric interactions with pentose. Do the purine nucleotides have similar interactions?

Question 67

Vegans (individuals who do not consume meat or meat products such as milk and eggs) may develop pernicious anemia if they take antibiotics. Explain.

Question 68

The amino acids glutamine and glutamate are central to amino acid metabolism. Explain.

Question 69

Both oxygen and nitrogen are present in the atmosphere as gases. Oxygen is reactive and nitrogen is relatively inert. What features of the two molecules account for this difference?

Question 70

Although they are consumed by animals in the diet, the purine and pyrimidine bases
(unlike fatty acids and sugars) are not used to generate energy. How does the body use them? What is the ultimate fate of dietary nitrogenous bases?

Question 71

Tyrosine is a nonessential amino acid in humans. Under what circumstances would it become an essential amino acid?

Question 72

The antibiotic sulfanilamide is an analogue of the para-aminobenzoic acid component of folate. Why would certain microorganisms die when exposed to sulfanilamide?

Question 73

Why do marathon runners prefer beverages with glucose instead of amino acids during a long run?

Question 74

By definition essential amino acids are not synthesized by an organism. Arginine is classified as an essential amino acid in infants even though it is part of the urea cycle. Explain.