Nitrogen + Amino Acid Metabolism

Question 1

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

Answer 1

E

Question 2

Choose correct options from statements below about the enzyme nitrogenase

I. can be found in most bacteria and a few invertebrate animals.
II. contains unique redox centres that contain both Fe and Mo.
III. relies on reducing agents and ATP hydrolysis.
IV. carries out a reaction that reduces atmospheric nitrogen to NO.

(a) I, II, III, IV
(b) II, III, IV
(c) II, III
(d) III, IV
(e) IV only

Answer 2

C

Question 3

The total cost of nitrogen reduction is at least ….. and ….. transferred electrons.

(a) 8 ATP; 4
(b) 12 ATP; 8
(c) 12 ATP; 6
(d) 16 ATP; 8
(e) 16 ATP; 6

Answer 3

D

Question 4

The overall function of the glutamate dehydrogenase reaction is

(a) insertion and removal of nitrogen in organic compounds
(b) production of urea
(c) distribution of nitrogen among different amino acids
(d) oxidation of ammonia to nitrate
(e) denitrification

Answer 4

A

Question 5

The function of the aminotransferase reaction is

(a) insertion and removal of nitrogen in organic compounds
(b) production of urea
(c) synthesis of carbamoyl phosphate
(d) distribution of nitrogen among different amino acids
(e) synthesis of the purine bases

Answer 5

D

Question 6

Amino acids which are required in the diet are called ……

(a) glycogenic
(b) ketogenic
(c) essential
(d) non-essential
(e) all of the above answers are correct

Answer 6

C

Question 7

Which of the following would be classed as essential amino acids?

(a) all of the acidic amino acids
(b) all of the branched chain amino acids
(c) all of the aromatic amino acids
(d) all of the sulphur-containing amino acids
(e) all of the aliphatic amino acids

Answer 7

B

Question 8

Which of the following amino acids is not derived from α-ketoglutarate?

(a) glutamate
(b) arginine
(c) histidine
(d) glutamine
(e) proline

Answer 8

C

Question 9

All of the following are catecholamines except _____

(a) histamine
(b) adrenaline
(c) dopamine
(d) noradrenaline
(e) Both (a) and (c)

Answer 9

A

Question 10

Aspartate is the precursor for which of the following amino acids?

(a) lysine
(b) threonine
(c) methionine
(d) All of the above
(e) None of the above

Answer 10

D

Question 11

Aspartic acid is synthesized from which of the following:

I. α-ketoglutarate
II. oxaloacetate
III. glutamine
IV. glutamate
V. NH 4+

(a) I, III
(b) I, IV
(c) II, III
(d) II, IV
(e) II, V

Answer 11

D

Question 12

In the first step in heme synthesis _____, _____ and condense to form δ-aminolevulinate.
(a) serine; methionine
(b) oxaloacetate; succinyl-CoA
(c) adenine; PRPP
(d) glycine; propionyl-CoA
(e) glycine; succinyl-CoA

Answer 12

E

Question 13

Which one of the following statements correctly describes the biosynthetic pathway for purine nucleotides?

(a) Purine deoxyribonucleotides are made by the same path as
ribonucleotides, followed by reduction of the ribose moiety.
(b) The first enzyme in the path is carbamoyl phosphate synthetase.
(c) The nitrogen in the purine base that is bonded to ribose in the nucleotide is derived originally from aspartate.
(d) The pathway occurs only in plants and bacteria, not in animals.
(e) The purine rings are first synthesised, then condensed with ribose phosphate

Answer 13

A

Question 14

Phosphoribosyl-pyrophosphate (PRPP) is a synthetic precursor for all of the following except:

(a) AMP.
(b) arginine.
(c) histidine.
(d) NAD +
(e) UMP

Answer 14

B

Question 15

The synthesis of purine and pyrimidine nucleotides differ in that:

(a) ATP is required in the synthesis of purines but not in the synthesis of pyrimidines.
(b) purine biosynthesis starts with the formation of phosphoribosyl pyrophosphate (PRPP), whereas pyrimidines incorporate the PRPP near the end of the pathway.
(c) purine formation requires a tetrahydrofolate derivative, whereas pyrimidine formation does not.
(d) pyrimidine biosynthesis is tightly regulated in the cell, whereas purine biosynthesis is not.
(e) pyrimidines go through many steps, adding a single carbon or nitrogen each time, whereas the basic skeleton for purines is formed by two main precursors.

Answer 15

B

Question 16

When gout patients are treated with allopurinol their blood and urine levels of ….. rise.

I. hypoxanthine
II. uric acid
III. xanthine
IV. urea
V. creatinine

(a) I, II
(b) I, III
(c) II, IV
(d) II, V
(e) III only

Answer 16

B

Question 17

Question 17
https://canvas.qut.edu.au/courses/15061/pages/week-10-nitrogen-and-amino-acid-metabolism-1?module_item_id=1456393

Answer 17

A

Question 18

Question 18
https://canvas.qut.edu.au/courses/15061/pages/week-10-nitrogen-and-amino-acid-metabolism-1?module_item_id=1456393

Answer 18

A

Question 19

Choose the correct answer from the list below. Not all answers will be used.

a) de novo
b) Lesch-Nyhan disease
c) ATP
d) nucleotide
e) gout
f) nucleoside
g) PRPP
h) phosphoribosylamine
i) pyrimidine
j) urate
k) Parkinson’s disease
l) salvage

i. The nucleotide …. is the most common “energy currency”?

ii. Assembly of a compound from simpler molecules is known as a …… pathway.

iii. Assembly of a compound from PRPP and a base is known as a …… pathway.

iv. A purine or pyrimidine base linked to a sugar is a …….

v. A purine or pyrimidine base linked to a sugar and to a phosphate ester is a …….

vi. High levels of urate cause the disease ……

vii. The final product of purine degradation is ……..

viii. A genetic mutation resulting in the absence of hypoxanthine-guanine phosphoribosyl transferase underlies …..

ix. The committed step in purine nucleotide biosynthesis is the conversion of ….. to phosphoribosylamine.

x. In ….. biosynthesis, the base is assembled first and then attached to ribose

Answer 19

i. Ans: c) ATP

ii. Ans: a) de novo

iii. Ans: l) salvage

iv. Ans: f) nucleoside

v. Ans: d) nucleotide

vi. Ans: e) gout

vii. Ans: j) urate

viii. Ans: b) Lesch-Nyhan disease

ix. Ans: g) PRPP

x. Ans: i) pyrimidine

Question 20

Why is nucleotide synthesis an important pathway for medical intervention? What types of disease could be treated using this information?

Answer 20

Interference of nucleotide synthesis could influence many different pathways because the nucleotides participate in so many processes. Especially important would be interference in the synthesis of nucleic acids to minimize or disrupt cell division, a strategy employed in
cancer therapy

Question 21

Why is it necessary to have protein in our (human) diets?

Answer 21

Protein provides the 9-10 essential amino acids that humans cannot synthesize. We need these amino acids for protein synthesis and for the production of a variety of products, such as histamine and serotonin, derived from the essential amino acids

Question 22

Give the name and structure of the glycolytic or tricarboxylic acid cycle intermediate that has the same carbon skeleton as:

(a) alanine
(b) glutamate
(c) aspartate

Answer 22

(a) pyruvate CH3—CO—COO–
(b) α-ketoglutarate –OOC—CH 2—CH 2—CO—COO–
(c) oxaloacetate –OOC—CH 2—CO—COO–

Question 23

Give the overall reaction that results from the action of glutamine synthetase

Answer 23

Answer:
glutamate + NH 4+ + ATP -> glutamine+ ADP + Pi

Question 24

Briefly describe the first committed step in the synthesis of heme

Answer 24

Briefly, glycine and succinyl-CoA condense to form δ-aminolevulinate

Question 25

Urea synthesis in mammals takes place primarily in tissues of the: (a) brain. (b) kidney. (c) liver. (d) bladder. (e) small intestine

Answer 25

C

Question 26

Which metabolic intermediate is not involved in the production of urea NH4+ via the urea cycle? (a) Aspartate (b) ATP (c) Carbamoyl phosphate (d) Malate (e) Ornithine

Answer 26

D

Question 27

Which of these amino acids below are both ketogenic and glucogenic? 1. Isoleucine 2. Valine 3. Histidine 4. Arginine 5. Tyrosine (a) 1 and 5 (b) 1, 3, and 5 (c) 2 and 4 (d) 2, 3, and 4 (e) 2, 4, and 5

Answer 27

A

Question 28

The human genetic disease phenylketonuria (PKU) can result from: (a) deficiency of protein in the diet. (b) inability to catabolise ketone bodies. (c) inability to convert phenylalanine to tyrosine. (d) inability to synthesise phenylalanine. (e) production of enzymes containing no phenylalanine

Answer 28

C

Question 29

In the human genetic disease maple syrup urine disease, the metabolic defect involves: (a) a deficiency of the vitamin niacin. (b) oxidative decarboxylation. (c) synthesis of branched chain amino acids. (d) transamination of an amino acid. (e) uptake of branched chain amino acids into liver

Answer 29

B

Question 30

If an amino acid is glucogenic, it will not be degraded to _____ (a) pyruvate (b) glutamate (c) fumarate (d) acetoacetate (e) α-ketoglutarate

Answer 30

D

Question 31

Which statement(s) about the enzyme carbamoyl phosphate synthetase is/are correct? (a) It produces an essential precursor in pyrimidine biosynthesis. (b) It is the enzyme that catalyses the synthesis of carbamoyl phosphate from bicarbonate and ammonium. (c) It is one of the most abundant enzymes in liver mitochondria. (d) Only (a) and (b) are correct. (e) Options (a), (b) and (c) are correct

Answer 31

E

Question 32

In the urea cycle which molecule is transported from the mitochondrial matrix to the cytosol? (a) arginine (b) citrulline (c) glutamate (d) carnitine (e) Ornithine

Answer 32

B

Question 33

The major regulated step of the urea cycle is which one of the following? (a) Carbamoyl phosphate synthetase I (b) Ornithine transcarbamoylase (c) Argininosuccinate synthetase (d) Argininosuccinate lyase (e) Arginase

Answer 33

A

Question 34

At the subcellular level where does the urea cycle occur? (a) mitochondrial matrix only (b) mitochondrial matrix and the mitochondrial inner membrane (c) mitochondrial matrix and cytosol (d) cytosol only (e) endoplasmic reticulum and cytosol

Answer 34

C

Question 34

The nitrogen atoms in urea are derived directly from which of the following compounds? (a) Ornithine and carbamoyl phosphate (b) Ornithine and aspartate (c) Ornithine and glutamate (d) Carbamoyl phosphate and aspartate (e) Carbamoyl phosphate and glutamine (f) Aspartate and glutamine

Answer 34

D

Question 35

The amino acids Ala, Cys, Gly, Ser, and Thr are all degraded to the metabolic intermediate _____ and are considered _____ (a) acetyl-CoA; glucogenic (b) acetyl-CoA; ketogenic (c) pyruvate; glucogenic (d) pyruvate; ketogenic (e) acetoacetate; ketogenic

Answer 35

C

Question 36

The following statements about phenylketonuria are correct except (a) Phenylalanine cannot be converted into tyrosine. (b) Urinary excretion of phenylpyruvate and phenyllacetate is increased. (c) Individuals with phenylketonuria will require a diet that contains tyrosine, but is low in phenylalanine. (d) It leads to increased synthesis of thyroid hormones, catecholamines and melanin. (e) Phenylketonuria is an autosomal recessive genetic disorder

Answer 36

D

Question 37

Which of the following statements about the carbon skeletons of amino acids are correct? Select all that apply. (a) Ketogenic amino acids can give rise to acetyl-CoA. (b) Glucogenic amino acids can give rise to glucose in starvation. (c) Ketogenic amino acids give rise to glucose. (d) Ketogenic amino acids are always converted to ketone bodies. (e) Some amino acids are both glucogenic and ketogenic

Answer 37

A, B, E

Question 38

Urea formation is energetically expensive, requiring the expenditure of 4 mol of ATP per mole of urea formed. However, NADH is produced by glutamate dehydrogenase prior to the step that donates NH + to carbamoyl phosphate and when fumarate is reconverted to oxaloacetate. How many ATP molecules are produced by the mitochondrial oxidation of NADH? What is the net ATP yield from or requirement for urea synthesis?

Answer 38

Mitochondrial oxidation of NADH generate 2.5 ATP molecules. The NADH molecules generated by glutamate dehydrogenase and formed during the conversion of fumarate to aspartate results in the synthesis of 2.5 ATP each, hence a total of 5 ATP. Therefore, the net ATP yield from urea synthesis will be 5 minus 4 ATPs, which equals 1 ATP per mole of urea.

Question 38

The same set of reactions converting fumarate to oxaloacetate via malate occur during the urea cycle and in the tricarboxylic acid (TCA) cycle. Describe the main differences between these reactions regarding their subcellular localisation, their purpose and the subsequent fate of oxaloacetate

Answer 38

During the urea cycle, fumarate is cleaved from argininosuccinate leaving arginine. Located in the cytosol, fumarate is metabolised to malate and further oxaloacetate by cytosolic isoforms of fumarase and malate DH (the same enzymes/reactions as in the TCA cycle in the mitochondrial matrix). Oxaloacetate is then converted to phosphoenolpyruvate (PEP) by PEP carboxykinase and used for gluconeogenesis, an anabolic pathway. This is different to the fate of oxaloacetate in the TCA cycle, where it is condensed with acetyl-CoA to citrate starting the cycle of stepwise oxidations to produce energy, a catabolic pathway

Question 39

Indicate which of the following amino acids are ketogenic, which are glucogenic, and which are both ketogenic and glucogenic. a) tyrosine b) lysine c) glycine d) alanine e) valine f) threonine

Answer 39

a) both b) ketogenic c) glucogenic d) glucogenic e) glucogenic f) both

Question 40

Degradation of amino acids yields compounds that are common intermediates in the major metabolic pathways. Explain the distinction between glucogenic and ketogenic amino acids in terms of their metabolic fates

Answer 40

The glucogenic amino acids are those that are catabolized to intermediates that can serve as substrates for gluconeogenesis: pyruvate and any of the four- or five-carbon intermediates of the citric acid cycle. Ketogenic amino acids are catabolized to yield acetyl-CoA or acetoacetyl-CoA, the precursors for ketone body formation

Question 41

Name one (1) amino acid whose oxidation proceeds via the intermediate shown: (a) pyruvate (b) oxaloacetate (c) α-ketoglutarate (d) succinyl-CoA (e) fumarate

Answer 41

(a) alanine, tryptophan, glycine, serine, cysteine. (b) aspartate, asparagine. (c) glutamate, glutamine, arginine, histidine, proline. (d) isoleucine, threonine, methionine, valine. (e) phenylalanine, tyrosine

Question 42

What type of symptoms and tissue damage occurs if there is a defect in the urea cycle? Describe (a) the fundamental nutritional problem faced by individuals with genetic defects in enzymes involved in urea formation, and (b) two approaches to treatment of these diseases

Answer 42

A defect in the urea cycle causes hyperammonemia (large amount of NH + ). Genetic defects become obvious immediately after birth. After lethargy and vomiting begins, coma and brain damage follow, most likely due to the high levels of Glu and Gln in the brain. (a) A defect in urea synthesis can result in the formation of toxic blood levels of ammonia from the breakdown of ingested proteins. Thus, it is desirable to limit the intake of amino acids. However, some amino acids are essential for humans (i.e., not biosynthesized) and hence must be ingested in adequate amounts. (b) One approach is to administer compounds that deplete the supply of glycine and glutamine. The replenishment of these amino acids removes ammonia from the blood. Another approach is to administer compounds that allow the liver to bypass the enzyme that is defective in the individual

Question 43

Describe the glucose–alanine cycle and its significance in amino acid metabolism

Answer 43

During prolonged exercise and fasting muscles use branched-chain amino acids as fuel. This degradation takes place in the muscle, but conversion to urea is not possible in this tissue, thus transport to liver is required. The amino nitrogen is removed by transamination to produce glutamate. The glutamate then transaminates with pyruvate producing alanine, which is released into blood and transported to the liver. In the liver the alanine is converted to pyruvate and the urea is metabolized to urea. The pyruvate is converted to glucose by gluconeogenesis and the glucose is transported back to the muscle via the bloodstream.