Chapter 18

Question 1

Nitrogenase carries out the energetically expensive reduction of ____ to ____

Answer 1

N2
NH3

Question 2

N2 fixation into NH3 happens in the

Answer 2

root nodules of legumes

Question 3

Ammonia is toxic at high concentrations so it must be

Answer 3

assimilated into useful compounds

Question 4

The formation of the amino acids, ____ and ____, from ammonia is of central importance in reducing ammonia concentrations and carrying nitrogen around the body

Answer 4

glutamate and glutamine

Question 5

Glutamate is formed by _____ of ketogluturate

Answer 5

reductive amination

Question 6

the reductive amination of ketoglutarate to glutamate is catalyzed by

Answer 6

glutamate dehydrogenase

Question 7

Glutamate is converted to glutamine by _____ via another amidation reaction

Answer 7

glutamine synthetase

Question 8

Transamination reactions transfer an amino group from one amino acid to an ______ to make a new amino acid

Answer 8

alpha keto acid

Question 9

Difference between an amino acid and an alpha keto acid

Answer 9

NH2 group for amino
O double bond C in keto acid

Question 10

Amino groups are donated to precursors via

Answer 10

transamination reactions

Question 11

Glutamate family in the TCA cycle

Answer 11

alpha-ketoglutarate
glutamate
glutamine
proline
arginine

Question 12

Aspartate family of the TCA cycle

Answer 12

Oxaloacetate
aspartate
asparagine
methionine
threonine
lysine
isoleucine

Question 13

Transamination reactions substrates and products

Answer 13

Substrate 1- amine donor
substrate 2- keto acid (amine receiver)
Product 1- alpha keto acid
Product 2- amino acid

Question 14

The amino acid NH2 donor becomes

Answer 14

an alpha keto acid

Question 15

Pyridoxal-5’-phosphate is a derivative of

Answer 15

pyridoxine

Question 16

Serine and one-carbon transfers are catalyzed by

Answer 16

serine hydroxymethyltransferase

Question 18

tetrahydrofolate is a derivative of _____ and is

Answer 18

folic acid
one-carbon group acceptor in this reaction

Question 19

Folic acid is a vitamin that

Answer 19

prevents birth defects and may lower risk of stroke

Question 20

Serine to glycine

Answer 20

serine becomes glycine upon donation of one carbon methylene group

Question 21

Carbon skeletons can follow

Answer 21

glucogenic or ketogenic pathways depending on the type of end product

Question 22

Glucogenic amino acids do what

Answer 22

catabolized to pyruvate or oxaloacetate and used to make glucose via gluconeogenesis

Question 23

ketogenic amino acids are catabolized to ___ and used to make ___

Answer 23

acetyl-CoA or acetoacetyl-CoA
ketone bodies when in excess

Question 24

Approximately 80% of excess nitrogen is excreted as

Answer 24

urea

Question 25

Urea is produced in the ___

Answer 25

liver

Question 26

In the urea cycle nitrogen is used to make _____ which is cleaved to release urea

Answer 26

arginine

Question 27

Nitrogen is used to make arginine comes from two sources _______

Answer 27

ammonia from oxidative deamination of AA
Aspartate donates amino group

Question 28

Carbonyl phosphate is an

Answer 28

amino group acceptor/donor

Question 29

Urea cycle steps

Answer 29

1.ornithine transcarbamoylase produces citrulline by transferring a carbamoyl group

2.argininosuccinate synthetase adds aspartate to citrulline in an ATP-dependent condensation reaction. Products AMP and PPi- which is subsequently hydrolyzed to 2 Pi- consumes 2 ATP equivalents

3. Argininsuccinase releases fumarate from argininosuccinate

4.arginase hydrolyzes arginine to generate urea and regenerate ornithine for another round of the urea cycle

Question 30

Ornithine enters the _____ and accepts amino group from carbamoyl phosphate to make citrulline

Answer 30

mitochondria

Question 31

Aspartate displaces AMP to form arginosuccinate- this is the ____

Answer 31

second nitrogen source

Question 32

Arginine is cleaved to form

Answer 32

urea
ornithine