Nitrogen metabolism

Question 1

nitrogen is found mostly in ??? and proteins

Answer 1

nucleic acids and proteins

Question 2

TRUE or FALSE: nitrogen can be found in:
- several cofactors (NAD, FAD, biotin, etc)
- many small hormones (epinephrine)
- many neurotransmitters (serotonin)
- many pigments (chlorophyll)
- many defence chemicals (amanitin in mushrooms)

Answer 2

TRUE

Question 3

what causes nitrogen to be virtually unusable by most organisms?

Answer 3

the highly resistant triple bond

Question 4

??? is the main process by which nitrogen-fixing bacteria and archea convert N2 to NH3 (biologically useful form)

Answer 4

nitrogen fixation

Question 5

TRUE or FALSE: Ammonia can be used by all organisms either directly or indirectly, after it has been converted to nitrites, nitrates or
amino acids

Answer 5

TRUE

Question 6

N2 and O2 → NO via lightning
(represents ???% of newly fixed N2)

Answer 6

25%

Question 7

N2 and H2 → NH3 (ammonia) via the
industrial Haber (Haber-Bosch) process (requires T > 400°C, P > 200 atm; represents ???% of newly fixed N2) (partly helped through ATP hydrolysis)

Answer 7

15%

Question 8

Fixation is the Reduction or Oxidation of N2 → NH3
/NH4+ (ammonia/ammonium)

Answer 8

Reduction

Question 9

Nitrification occurs when Bacteria Oxidise or Reduce NH3 into NO2– (nitrite) and NO3– (nitrate)

Answer 9

oxidise

Question 10

Denitrification is the process where NO3– / NO2– is Reduced or Oxidised to N2 under anaerobic conditions

Answer 10

Reduced

Question 11

TRUE or FALSE:
Anammox: Anaerobic ammonia oxidation = alternative pathway back to N2

Answer 11

TRUE

Question 12

Assimilation: Plants and microorganisms reduce NO3– and NO2– to NH3/NH4+ via nitrate ??? and nitrite ???

Answer 12

reductases

Question 13

Following Fixation or Assimilation
ammonia in its reduced form (NH4+) is assimilated into ??? and
biomolecules ==> Nitrogen CYCLE part of nitrogen web

Answer 13

amino acids

Question 14

Nitrogen CYCLE part of nitrogen web where:
1. Animals eat plants as source of ???
2. NH4+ in plants is incorporated into AAs and other N-containing biomolecules
3. Organisms die, return NH4+ to soil.
4. Nitrifying bacteria again convert NH4+ /NH3 to NO2– and NO3–

Answer 14

amino acids

Question 15

TRUE or FALSE: transamination does NOT provide nitrogen

Answer 15

FALSE it is a source of nitrogen

Question 16

??? is the transfer of an amino group from one molecule to another

Answer 16

Transamination

Question 17

transamination is catalysed by ??? and use pyridoxal phosphate (PLP) as a cofactor

Answer 17

aminotransferases

Question 18

Transamination as N source:
- L-Glutamate acts as a temporary storage of N
- L-Glutamate DONATES or RECEIVES the amino group when needed for amino acid biosynthesis = readily reversible
- Glutamate is the source of amino groups for most other amino acids in mammals

Answer 18

DONATES

Question 19

Transamination as N source:
α-ketoglutarate + L-amino acid <–> L-??? + α-ketoacid

Answer 19

glutamate

Question 20

Ammonia (NH4+) is Incorporated into Biomolecules through Glutamate and ???

Answer 20

Glutamine

Question 21

Glutamine is made from ??? by glutamine synthetase in a two-step process.
1. Phosphorylation of ??? creates a good leaving group that can be easily displaced by ammonia
2. glutamate dehydrogenase -
catalyses the incorporation of ammonium into α-ketoglutarate to produce ???

Answer 21

glutamate
glutamate
glutamate

Question 22

The enzyme - glutamate dehydrogenase - catalyses the incorporation of ammonium into
??? to produce glutamate

Answer 22

α-ketoglutarate

Question 23

TRUE or FALSE: incorporation of ammonium into α-ketoglutarate to produce glutamate is the minor pathway of glutamate formation

Answer 23

TRUE

Question 24

What enzyme is a Primary Regulatory Point in Nitrogen Metabolism?

Answer 24

glutamine synthetase

Question 25

glutamine synthetase plays a central role in the conversion of toxic free NH3 to glutamine and in the metabolism of ???

Answer 25

amino acids

Question 26

glutamine synthetase undergoes ??? regulation by six end products of glutamine metabolism

Answer 26

cumulative

Question 27

glutamine synthetase is regulated by ??? regulation and inhibited by adenylylation

Answer 27

allosteric regulation

Question 28

Adenylylation is a post-translational modification whereby AMP binds to a hydroxyl group of a molecule via adenylyltransferase, inhibiting ???

Answer 28

glutamine synthetase

Question 29

Adenylylation is indirectly inhibited by α-ketoglutarate and ATP to stop inhibiting ???

Answer 29

glutamine synthetase

Question 29

Adenylylation is indirectly stimulated by glutamine and Pi to inhibit ???

Answer 29

glutamine synthetase

Question 30

amino acid biosynthesis is through catabolism or anabolism?

Answer 30

anabolism

Question 31

Carbon skeletons come from intermediates of * Glycolysis * Citric acid cycle * ???

Answer 31

Pentose phosphate pathway

Question 32

TRUE or FALSE: A deficiency of one amino acid does not impact the synthesis of all proteins required for life, it only impacts a few that share similar pathways

Answer 32

FALSE: A deficiency of one amino acid impacts the synthesis of all proteins required for life

Question 33

a-ketoglutarate, pyruvate, 3-phosphoglycerate, oxaloacetate, ribose-5-phosphate and phosphoenolpyruvate + erythrose 4-phosphate are the 6 major NON-ESSENtial or ESSENTIAL Amino Acid Biosynthetic Families?

Answer 33

NON-ESSENTIAL

Question 34

Nonessential amino acids (except Arg) are synthesised by simple reactions ??? steps

Answer 34

1-5

Question 35

Essential amino acids are synthesised by more complex reactions ??? steps

Answer 35

5-16 steps

Question 36

Regulation of threonine deaminase: Threonine is converted into a-ketobutyrate in the committed step = synthesis of isoleucine. ??? catalyzes this step and is inhibited by isoleucine (its product) and activated by valine, the product of a parallel pathway.

Answer 36

threonine deaminase

Question 37

CATABOLISM or ANABOLISM of amino acids accounts for only 10-15% of energy production

Answer 37

CATABOLISM

Question 38

Glycolysis and fatty acid oxidation are more active than the catabolism of ??? in the production of energy

Answer 38

aminoa cids

Question 39

Catabolic pathways converge to 6-7 major products, all which enter TCA cycle. From here the carbon skeletons can be used for gluconeogenesis or formation of ??? bodies

Answer 39

ketone bodies

Question 40

decarboxylation reactions turn amino acids into neurotransmitters such as ??? which are correlated with, among other things, changes in blood pressure and neuro/psychiatric disorders.

Answer 40

catecholamines

Question 41

amino acids also undergo decarboxylation reactions during hormone synthesis, i.e. y-aminobutyrate and ???

Answer 41

histamine

Question 42

Glutathione (GSH) is present in most cells at high amounts and is a reducing agent/???

Answer 42

antioxidant

Question 43

GSh keeps proteins and metal cations reduced, keeps redox enzymes in a ??? state and removes toxic reactive oxygen species (ROS)

Answer 43

reduced

Question 44

Glutathion (GSH) is Oxidized or Reduced to a dimer (GSSG

Answer 44

Oxidised

Question 45

TRUE or FALSE: nitric oxide is important biologically for neurotransmission, blood pressure regulation, blood clotting and immunity

Answer 45

TRUE

Question 46

Nitric Oxide is synthesised from ??? via nitric oxide synthase using NADPH

Answer 46

Arginine