Deck 17: Amino Acid Metabolism

Question 1

Which of the following is the correct net reaction of nitrogen fixation in bacteria?

A) N₂ + 8H⁺ + 8e ^- + 16 ATP + 16 H₂O $\rightarrow$ 2NH₃ + H₂ + 16 ADP + 16 P_i
B) N₂ + 8H⁺ + 8e ^- + 16 ADP + 16 H₂O $\rightarrow$ 2NH₃ + H₂ + 16 ATP + 16 P_i
C) 2N₂ + 8H⁺ + 8e ^- + 16 ATP + 16 H₂O $\rightarrow$ NH₃ + 4H₂ + 16 ADP + 16 P_i
D) 2NH₃ + H₂ + 16 ADP + 16 P_i $\rightarrow$ N₂ + 8H⁺ + 8e ^- + 16 ATP + 16 H₂O

Answer 1

N₂ + 8H⁺ + 8e ^- + 16 ATP + 16 H₂O $\rightarrow$ 2NH₃ + H₂ + 16 ADP + 16 P_i

Question 2

Using nitrogenase to reduce N₂ should require 2 ATP to be invested, but it actually takes 16 ATP. Why?

A) It is harder to break the nitrogen triple bond than expected and requires more energy input.
B) Extra energy is required to produce H_2.
C) To regenerate the MoFe protein requires the input of ATP.
D) To keep the nitrogenase complex associated requires an input of 4 ATP.

Answer 2

Extra energy is required to produce H_2.

Question 3

Agricultural fertilizers provide the ground with nitrate and nitrite, but only ammonia can be assimilated by plants. What process converts nitrate and nitrite to ammonia?

A) nitrification
B) ammonia assimilation
C) nitrogen fixation
D) nitrogen assimilation

Answer 3

nitrification

Question 4

Nitrite is oxidized by Nitrobacter bacteria to

A) NO_2.
B) NO₂ ^- .
C) NO ^- .
D) NO₃ ^- .

Question 5

How does biological fixation convert nitrogen to ammonia?

A) by reducing nitrogen
B) by combining nitrogen with carbon
C) through the ATP-dependent process catalyzed by nitrogenase complex
D) through the NADH-dependent process catalyzed by glutamate dehydrogenase

Question 6

How does atmospheric fixation occur given the high energy barrier to convert nitrogen to nitrogen oxides?

A) through the oceans that break the triple bond of nitrogen and allow for the combination with water
B) through clouds that allow for nitrogen to combine with oxygen
C) in the soil by bacteria that reduce nitrogen to ammonia
D) through lightning that breaks the triple bond of nitrogen and allows for the combination with oxygen

Question 7

The process of nitrogen fixation reduces N₂ to

A) NAD⁺.
B) nitrate.
C) ammonia.
D) nitrite.

Question 8

What is the net reaction of nitrogen assimilation in plants?

A) "Glutamate + ADP + P_i + NADP⁺ $\rightarrow$$\alpha$ -Ketoglutarate + NH₄⁺ + ATP + NADPH + H⁺"
B) " $\alpha$ -Ketoglutarate + NH₄⁺ + ATP + NADPH + H⁺ $\rightarrow$ Glutamate + ADP + P_i + NADP⁺
C) " $\alpha$ -Ketoglutarate + NH₄⁺ + ADP + NADPH + H⁺ $\rightarrow$ Glutamate + ATP + P_i + NADP⁺"
D) " $\alpha$ -Ketoglutarate + NH₄⁺ + ATP + NADP⁺ + H⁺ $\rightarrow$ Glutamate + ADP + P_i + NADPH"

Question 9

Because nitrogenase is inhibited by oxygen, under what conditions can the enzyme operate to reduce N₂?

A) aerobic conditions
B) anaerobic conditions
C) high pressure
D) high temperature

Question 10

Nitrogen in biological compounds ultimately comes from what source?

A) ammonia
B) nitrate
C) nitrogen gas
D) bacteria

Question 11

To increase the efficiency of the nitrogenase reaction, some plants have symbionts. The plant increases the efficiency of the reaction by providing , whereas bacteria provide(s) .

A) fumerate and malate; additional NH₃
B) fumerate and malate; ATP
C) ATP; amino acids
D) NADH; ATP

Question 12

The Haber process is 98% efficient. How does it achieve that level of efficiency?

A) low temperatures and atmospheric pressure
B) low pressures and recycling unreacted nitrogen
C) high pressures and recycling nitrogen
D) high pressures and high concentrations of nitrogen

Question 13

Both Nitrosomonas and Nitrobacter have a key role in nitrification. Nitrosomonas produces __________, whereas Nitrobacter produces .

A) ammonia; nitrite
B) nitrite; nitrate
C) nitrate; nitrite
D) nitrite; ammonia

Question 14

The 10 amino acids that animals need to take in through their diet are called the __________ amino acids.

A) common
B) essential
C) optional
D) degradation

Question 15

If plants and bacteria were unable to produce glutamate from ammonia, a possible outcome would be that plants would

A) be able to produce more nucleotides.
B) no longer be able to produce other amino acids.
C) not be able to complete glycolysis.
D) be able to produce more ATP.

Question 16

What are the four key enzymes in nitrogen fixation and assimilation in plants and bacteria?

A) nitrogenase synthetase, glutamine complex, glutamate synthase, glutamate dehydrogenase
B) nitrogenase complex, glutamine synthetase, glutamate synthase, glutamate dehydrogenase
C) glutamine synthetase, glutamate synthase, glutamate dehydrogenase, glutamate oxidase
D) nitrogenase complex, glutamine synthetase, glycine synthase, glutamine dehydrogenase

Question 17

Which three enzymes mediate ammonia assimilation?

A) glutamine synthase, glutamate synthetase, glutamate hydrogenase
B) glutamine synthetase, glutamate synthase, glutamate dehydrogenase
C) glutamine oxidase, glutamate reductase, glutamate dehydrogenase
D) glutamine dehydrogenase, glutamate synthase, glutamate oxidase

Question 18

In the nitrogen cycle, one main method for ammonia entering is

A) decomposition of organic material by invertebrates.
B) from the atmosphere.
C) through denitrification.
D) by leghemoglobin.

Question 19

Bacteria in the genus Nitrosomonas are able to oxidize ammonia to what final product?

A) NO₂
B) NO₃ ^-
C) NO₄ ^-
D) NO₂ ^-

Question 20

The nitrogen balance in the biosphere incorporates which of the following processes?

A) nitrogen fixation, nitrogen assimilation, and nitrate reduction
B) nitrogen oxidation and nitrogen reduction
C) nitrogen fixation, nitrification, and nitrate reduction
D) nitrogen oxidation and nitrate assimilation

Question 21

Aminotransferase reactions operate at $\Delta$ G $\degree$ ^' $\approx$ 0. What occurs when there is high substrate availability?

A) Mostly reactants are made.
B) Mostly products are made.
C) Equal amount of products and reactants are made.
D) This reaction is thermodynamically unfavorable.

Question 22

How can the body easily adjust the relative levels of some amino acids using aminotransferases?

A) Add ATP to the cell to produce more amino acids.
B) Use common intermediates to interconvert between amino acids.
C) Phosphorylate the amino acids to prevent them from being used.
D) Remove NADH from the cell to produce more amino acids.

Question 23

A negative nitrogen balance in a person would be an indicator of

A) accumulation of nitrogen in the body.
B) a diet heavy in protein.
C) starvation.
D) overall good health.

Question 24

Nitrogen balance is best described as when the daily intake of equals the amount of __________ lost by excretion.

A) ammonia; nitrogen
B) nitrogen; nitrogen
C) glucose; glucose
D) nitrogen; ammonia

Question 25

In the absence of ATP for glutamine synthetase to use, what would happen to the concentration of glutamine in the cell?

A) increase
B) decrease
C) no change
D) Not enough information is given.

Question 26

Aminotransferase reaction is an example of what kind of kinetics?

A) ternary
B) ping-pong
C) cooperative
D) reversible

Question 27

How many different forms of pyridoxal phosphate are observed in the aminotransferase reaction?

A) 7
B) 6
C) 5
D) 4

Question 28

Glutamine synthetase uses ammonia to covert glutamate into

A) "glutamine.
B) "nitrate."
C) " $\alpha$ -ketoglutarate."
D) "histidine."

Question 29

Which of the following is the correct net reaction for the combined reaction of glutamine synthetase and glutamate synthase?

A) " $\alpha$ -ketoglutarate + NH₄⁺ + ATP + NADH + H⁺ $\rightarrow$ NAD⁺ + ADP + P_i + glutamate"
B) "NAD⁺ + ADP + P_i + glutamate $\rightarrow$ $\alpha$ -ketoglutarate + NH₄⁺ + ATP + NADH + H⁺"
C) " $\alpha$ -ketoglutarate + NH₄⁺ + ATP + NADH + H⁺ $\rightarrow$ NAD⁺ + ADP + P_i + glutamine"
D) "glutamate + NH₄⁺ + ATP + NADH + H⁺ $\rightarrow$ NAD⁺ + ADP + P_i + $\alpha$ -ketoglutarate"

Question 30

The two mechanisms to regulate protein ubiquitination are biochemical changes to

A) target proteins and E1 ligases.
B) E1 and E2 ligases.
C) target proteins and E3 ligases.
D) the E2-ubiquitin-E3 complex.

Question 31

Compare the function of pepsin with that of secretin.

A) Pepsin cleaves trypsin, whereas secretin activates proteolytic zymogens.
B) Pepsin activates trypsinogen, whereas secretin neutralizes pH back to 7.
C) Pepsin denatures proteins, whereas secretin cleaves polypeptide bonds.
D) Pepsin cleaves polypeptide bonds, whereas secretin neutralizes pH back to 7.

Question 32

After food enters the stomach, gastrin triggers the release of and secretion of .

A) gastric juices; pepsinogen
B) gastric juices; chyme
C) chime; enteropeptidase
D) secreton; enteropeptidase

Question 33

What specific characteristic must a target protein have to be recognized by an ubiquitinating protein?

A) "phosphorylated residue"
B) "N terminus"
C) "C terminus"
D) " $\alpha$ -helix"

Question 34

In the duodenum, enteropeptidase

A) cleaves trypsinogen to form trypsin.
B) cleaves chymotrypsinogen to form chymotrypsin.
C) generates peptides and amino acids.
D) neutralizes the pH of the duodenum to a pH of 7.

Question 35

Given that glutamate dehydrogenase has a K_m of 1 mM and $\Delta$ G of +30 kJ/mol, glutamate dehydrogenase only operates best when

A) there is a high concentration of nitrogen available.
B) there is a low concentration of nitrogen available.
C) operates regardless of nitrogen concentration.
D) Not enough information is given.

Question 36

In the overall reaction of aminotransferase, how many amino acids are produced?

A) 1
B) 2
C) 3
D) 0

Question 37

It is important that proteolytic enzymes in the lysosome are optimized to work at low pH because low pH

A) enhances protein denaturing.
B) deactivates cysteine proteases.
C) makes it easier for ATP to be converted to ADP + P_i.
D) enhances the degradation of ubiquitinated proteins.

Question 38

What would the products be for the reaction below?

A) " $\alpha$ -keto acid and glutamate"
B) "oxaloacetate and glutamate"
C) "pyruvate and glutamate"
D) "histidine and glutamate"

Question 39

Adenylylation of Try397 regulates glutamine synthetase by

A) lowering activation energy.
B) inhibiting activity.
C) increasing activation energy.
D) increasing rate of reaction.

Question 40

Eukaryotic proteasome selectively degrade which type of proteins?

A) all proteins; they are not selective
B) ubiquitinated proteins
C) phosphorylated proteins
D) ATP-dependent proteins

Question 41

A person who has alkaptonuria is easily diagnosed from his or her black urine. What causes the black color?

A) oxidation of phenylalanine
B) oxidation of homogentisate
C) reduction of acetoacetyl-CoA
D) dehydration

Question 42

Which intermediate is shared by the urea cycle and the citric acid cycle?

A) citrulline
B) argininosuccinate
C) aspartate
D) malate

Question 43

The urea cycle's function is to the body of an organism.

A) remove excess sugar from
B) remove excess water-soluble vitamins from
C) remove excess nitrogen from
D) add additional nitrogen to

Question 44

Using the figure below, determine which of the following is NOT a final product from group 1 amino acid degradation.

A) glycine
B) pyruvate
C) acetoacetyl-CoA
D) acetyl-CoA

Question 45

What nitrogen source is used to produce carbamoyl phosphate?

A) alanine
B) urea
C) ammonia
D) glutamine

Question 46

Which of the following is the net reaction of the urea cycle?

A) Urea + Fumerate + 2 ADP + 2P_i + AMP + PP_i $\rightarrow$ NH⁺ + HCO₃^- + aspartate + 3ATP
B) NH⁺ + HCO₃ ^- + aspartate + 3ATP $\rightarrow$ urea + fumerate + 2 ADP + 2P_i + AMP + PP_i
C) NH⁺ + HCO₃ ^- + fumerate + 3ATP $\rightarrow$ urea + aspartate + 2 ADP + 2P_i + AMP + PP_i
D) NH⁺ + HCO₃ ^- + aspartate + 2 ADP + 2P_i + AMP + PP_i $\rightarrow$ urea + fumerate + 3ATP

Question 47

Cells cannot store amino acids that accumulate as a result of protein degradation. The carbon skeletons that remain

A) enter the urea cycle.
B) are used to produce new amino acids.
C) enter the citrate cycle.
D) are used to produce DNA and RNA.

Question 48

Which intermediates of the Krebs bicycle would be found in the cytosol?

A) fumerate and argininosuccinate
B) citrulline and malate
C) arginine and oxaloacetate
D) urea and ammonia

Question 49

The recycling of fumerate helps offset the energy cost of the urea cycle because fumerate helps generate

A) arginine to produce 2 ATP.
B) citrulline to produce NADPH, which can generate 3 ATP.
C) oxaloacetate to produce NADH, which can generate 2.5 ATP.
D) urea, which will make more ATP.

Question 50

If no NAD⁺ was available, the group 2 amino acid degradation pathway would experience a

A) buildup of urea.
B) buildup of glutamate.
C) depletion of proline.
D) depletion of histidine.

Question 51

Alanine, cysteine, glycine, and serine are all considered amino acids.

A) glucogenic
B) ketogenic
C) nonessential
D) urea

Question 52

If there was a loss of efficiency in the urea cycle, there would be a buildup of

A) fumarate.
B) urea.
C) glutamine.
D) glucose.

Question 53

Which of the following is the key regulated enzyme in urea synthesis?

A) carbamoyl phosphate synthetase I
B) glutamate dehydrogenase
C) arginase
D) argininosuccinase

Question 54

A no-protein diet with high doses of L-arginine helps patients with argininosuccinase deficiency because it __________ the concentration of _.

A) increases; fumerate that is metabolized by the citric acid cycle to lower ammonia levels
B) increases; ammonia in the diet to keep them regulated
C) increases; ornithine that is needed to maintain flux through the urea cycle
D) decreases; citrulline to prevent ammonia toxicity

Question 55

When amino acids from dietary proteins enter a cell, how are they able to enter the urea cycle?

A) through conversion to glutamine
B) through conversion to aspartate
C) by degrading down to ammonia
D) by getting phosphorylated

Question 56

Alkaptonuria is a disease coming from a deficiency in which pathway?

A) group 1
B) group 2
C) group 3
D) urea

Question 57

What is a possible outcome to the urea cycle if the cell is unable to produce enough aspartate?

A) Flux would be accelerated through the cycle.
B) There would be a buildup of citrulline.
C) There would be a buildup of urea.
D) The cycle would maintain equilibrium.

Question 58

Group 2 pathways can be correctly described as pathways that

A) degrade glucogenic amino acids to generate $\alpha$ -ketoglutarate.
B) convert phenylalanine to tyrosine.
C) degrade alanine.
D) convert fumerate to oxaloacetate.

Question 59

In the production of urea, the carbon atom comes from

A) water.
B) carbamoyl phosphate.
C) aspartate.
D) the citrate cycle.

Question 60

Glucogenic amino acids give rise to which molecule?

A) pyruvate
B) urea
C) ketone bodies
D) glucose

Question 61

Arginine, leucine, and lysine are all essential amino acids. This means that they are

A) only available from a person's diet.
B) produced from other intermediates.
C) not needed for a body to function.
D) the main intermediates to the urea cycle.

Question 62

A person unable to produce new melanocytes is likely to have

A) black hair.
B) red hair.
C) gray hair.
D) hair loss.

Question 63

Using the figure below, illustrate the two final products and identify the amino group on glutamine that gets transferred.

Question 64

A possible outcome if E. coli was depleted in NADPH would be

A) buildup of lysine.
B) depletion of asparagine.
C) buildup of aspartate.
D) depletion of methionine.

Question 65

The shikimate pathway can be defined as the pathway that involves the

A) condensation of phosphoenolpyruvate and erythrose-4-phosphate.
B) synthesis of essential amino acids from pyruvate.
C) synthesis of essential amino acids from oxaloacetate.
D) condensation of oxaloacetate and shikimate.

Question 66

What amino acid serves as the precursor to heme?

A) histidine
B) asparagine
C) glycine
D) glutamine

Question 67

Jaundice is indicative of what process working inefficiently?

A) heme synthesis
B) bilirubin removal from blood
C) urea synthesis
D) amino acid degradation

Question 68

Which of the following is the reaction for nitric oxide synthase?

A) citrulline + NO + 1.5 NADP⁺ $\rightarrow$ L-arginine + 1.5 NADPH + H⁺ + 2O₂
B) L-arginine + 1.5 NADPH + H⁺ + 2O₂ $\rightarrow$ citrulline + NO + 1.5 NADP⁺
C) L-arginine + 1.5 NADPH + H⁺ + 2O₂ $\rightarrow$ dopamine + NO + 1.5 NADP⁺
D) L-arginine + 1.5 NADP⁺ + H⁺ + 2O₂ $\rightarrow$ citrulline + NO + 1.5 NADPH

Question 69

Aspartate is a(n) amino acid, so if a person had a diet that contained no aspartate, .

A) essential; death would occur
B) nonessential; aspartate could be synthesized from other intermediates
C) essential; aspartate could be synthesized from other intermediates
D) nonessential; death would occur

Question 70

Diseases affecting heme biosynthesis as a result of deficiencies in the heme biosynthetic pathway are called

A) porphyrias.
B) albinism.
C) shikimate.
D) alkaptonuria.

Question 71

Which metabolic process is the cause of albinism?

A) inefficient production of dopamine
B) the enzyme tyrosinase working inefficiently
C) overproduction of NADPH
D) low levels of ATP available in the cell

Question 72

What purpose does nitrogen fixation and assimilation serve in the biosphere?

Question 73

What is the mechanism by which Roundup works?

A) Glyphosate is a competitive inhibitor to plant EPSP synthase.
B) Urea is a competitive inhibitor to plant chorismate synthase.
C) Glyphosate is an activator to plant EPSP synthase.
D) Anthranilate is an activator to chorismate synthase.

Question 74

Why do angina patients carry nitroglycerine with them?

A) as a rapid source of NO for blood vessel dilation
B) as a source of ammonia for muscle relaxation
C) to inhibit acetylcholine release from neurons
D) to inhibit cGMP phosphodiesterase

Question 75

A person who has phenylketonuria will have a buildup of which molecule in the cell?

A) tyrosine
B) phenylalanine
C) pyruvate
D) alanine

Question 76

What are the allosteric regulators of glutamine synthetase?

Question 77

What are the six steps of the nitrogenase reaction?

Question 78

What molecule signals the endothelial cell to produce NO?

A) dopamine
B) phosphate
C) acetylcholine
D) citrulline

Question 79

A person who has phenylketonuria must avoid which food additive?

A) protein
B) methanol
C) aspartame
D) phenylalanine

Question 80

What is the difference between nitrogen fixation and nitrogen assimilation?