Chapter 24 Amino Acid Synthesis

Front 1

nitrogen fixation

Back 1

biosynthetic process that reduces N2 to NH3
we can't do it--bond energy is huge (225 kcal/mol)

Front 2

how is nitrogen fixed?

Back 2

electrons are carried to nitrogenase by Fe-S clusters
nitrogenase is a complex, ATP is required to bring reductase and nitrogenase together
requires A LOT of ATP

Front 3

synthesis of glutamate
(what enzyme catalyzes reaction)

Back 3

important because in incorporates ammonia into metabolites
alpha-ketoglutarate + NH4+ goes through schiff base intermediate which is reduced to glutamate
enzyme: glutamate dehydrogenase

Front 4

synthesis of glutamine

Back 4

another way to assimilate NH4+ into metabolites--has very high affinity for NH4+, so can sequester it when it is scarce
enzyme: glutamine synthetase
reaction proceeds via activation of glutamate by ATP to acyl-phosphate intermediate
key regulatory step in N metabolism

Front 5

regulation of glutamine synthesis

Back 5

adenylation (covalent attachment of AMP catalyzed by adenylate transferase) deactivates glutamine synthetase
adenylate transferase is activated by glutamine, inhibited by alpha-ketoglutarate

Front 6

synthesis of arginine

Back 6

synthesized in urea cycle--arginosuccinate is split into arginine and fumarate by argininosuccinase
(comes originally from glutamate, but goes through ornithine into urea cycle)

Front 7

synthesis of tyrosine
(what is the enzyme)

Back 7

first step in degradation of phenylalanine by phenylalanine hydroxylase yields tyrosine

Front 8

synthesis of aspartate

Back 8

OAA is transaminated into aspartate

Front 9

synthesis of alanine

Back 9

pyruvate is transaminated into alanine

Front 10

transaminations involve....

Back 10

pyridoxal phosphate and schiff base formation

Front 11

glutamate can be made into what amino acids?

Back 11

glutamine, proline, and arginine

Front 12

synthesis of serine (and what amino acids can be made from serine?)

Back 12

from 3-phosphoglycerate (3 steps including transamination) to serine then cysteine and glycine come from serine

Front 13

why do we see only L-isomers in nature?

Back 13

transamination enzymes hold keto acids in a particular way so that only L-isomer results

Front 14

synthesis of arginine and proline proceed through what intermediates?

Back 14

activated acyl-phosphate intermediate and glutamic semialdehyde
(synthesized from glutamate)

Front 15

hydroxyproline

Back 15

found in proteins (collagen) but not synthesized as amino acid--made when protein is synthesized
requires ascorbic acid

Front 16

synthesis of asparagine

Back 16

derived from aspartate with addition of amino group from glutamate
uses acyl-adenylate intermediate

Front 17

where does 3-phosphoglycerate come from?

Back 17

glycolysis (intermediate)

Front 18

tetrahydrofolate

Back 18

folic acid: vit. B9
coenzyme--universal carrier of carbon 1 groups (these carbon groups can be interconverted--methyl to methylene, etc.)
seen in reaction changing serine into glycine
doesn't have high transfer potential

Front 19

s-adenosylmethionine

Back 19

activated methyl group with high transfer potential
important methyl donor in biological synthesis

Front 20

activated methyl cycle

Back 20

synthesizes methionine
homocysteine-->methionine-->S-adenosyl-methionine-->S-adenosyl-homocysteine
vitamin B12 is used by methionine synthase
active CH3 is released in coversion from SAM to SAH

Front 21

SAM and ripening of fruit

Back 21

(S-adenosylmethionine) SAM is a precursor of ethylene which induces ripening in fruit

Front 22

homocysteine is ___-donor in synthesis of _____

Back 22

SH; cysteine
(remember S from homocysteine, C from Serine)

Front 23

homocysteine is toxic in what situation?

Back 23

in arteries
cystathionine synthase deficiency leads to increased homocysteine levels
homeostasis of homocysteine requires B6, B9, B12
elevated homocysteine linked to heart attacks

Front 24

nitric oxide
(also what is it derived from)

Back 24

a second messenger derived from arginine
diffuses freely, short half-life
regulates blood flow, platelet aggregation, immune response
free radical

Front 25

porphyrins

Back 25

synthesized from glycine and succinyl CoA
porphyrins + Fe=heme

Front 26

cutaneous porphyria

Back 26

inherited enzyme defects of heme synthesis
cutaneous porphyria--uroporphyrine intermediates accumulate
skin becomes photosensitive
individuals avoid sunlight
some symptoms aleviated by infusion of heme

Front 27

biliverdin

Back 27

intermediate in breakdown of heme--involved in color seen in bruises, jaundice

Front 28

methylcobalamin

Back 28

coenzyme responsible for transferring methyl group from methyl-tetrahydrofolate to homocysteine to make methionine
enzyme catalyzing is methionine synthase

Front 29

tetrahydrofolate plays a role in the synthesis of what 2 amino acids?

Back 29

serine--->glycine
homocysteine-->methionine

Front 30

2 amino acids that come from homocysteine

Back 30

methionine and cysteine (SH from homocysteine, C from Serine)

Front 31

glutathione peroxidase

Back 31

peroxides are reduced at the expense of glutathione
NADPH is used to regenerate glutathione