Nitrogen Metabolism I and II

Question 1

nitrogen balance

Answer 1

in a normal human adult N(in) = N(out)

in a growing child, adolescent, pregnancy N(in) > N(out)

eating too little protein or lacking essential amino acids N(in) < N(out)

Question 2

three sources for the amino acid pool

Answer 2

degradation of body proteins

dietary proteins

synthesis of non-essential amino acids

Question 3

three fates of amino acids in the amino acid pool

Answer 3

synthesis of body proteins

precursors for essential nitrogen-containing small molecules

conversion to clucose, glycogen, fatty acids, or CO2

Question 4

two main routes for amin removal

Answer 4

alanine aminotransferase transfers amino group from alanine to a-KG to make glutamate

aspartate aminotransferase transfers amino groups from glutamate to oxaloacetate to form aspartate

Question 5

What coenzyme is required for aminotransferase reactions?

Answer 5

pyridoxal phosphate, a derivative of vitamin B6

Question 6

What are the main sources for the nitrogen cycle?

Answer 6

Question 7

What amino acid undergoes rapid oxidative deamination, and what is the enzyme that catalyzes this?

Answer 7

glutamate, glutamate dehydrogenase

uses NAD+ or NADP+ as the coenzyme

GTP is an allosteric inhibitor and ADP is an allosteric activator

Question 8

What happens to D-amino acids from plants?

Answer 8

metabolized by D-amino acid oxidase in a FAD-dependent reaction in peroxisomes

Question 9

Which amino acids do not undergo transamination reactions?

Answer 9

lysine, threonine, proline, and HO-proline

Question 10

alanine aminotransferase reaction

Answer 10

Question 11

aspartate aminotransferase reaction

Answer 11

Question 12

glutamate dehydrogenase reaction

Answer 12

Question 13

Describe the glucose/alanine cycle.

Answer 13

transfers nitrogen to the liver, ammonia in the blood is toxic so adds it onto alanine for transport

done primarily in muscle tissue

Question 14

Describe the process of transporting nitrogen through blood as glutamine.

Answer 14

primarily used by peripheral tissues, but if there is a lot of tissue breakdown, muscle will use this process as well

Question 15

Describe the oxidative deamination process by amino acid oxidases in peroxisomes.

Answer 15

Flavoprotein and FAD are the same

Question 16

Describe the urea cycle.

Answer 16

Ornithine is an amino acid not used in proteins and is recycled

fumarate is a byproduct, connecting this with the TCA cycle

Question 17

three mechanisms that regulate the urea cycle

Answer 17

substrate availability in a feed-forward mechanism

allosteric activation of carbamoyl phosphate synthease I (CPSI) by N-acetylglutamate (NAG)

induction/repression of urea cycle enzyme synthesis during high protein diet or during starvation

Question 18

regulation of CPSI

Answer 18

main method of regulation, senses how much amine is coming in

Question 19

How are the urea and TCA cycles linked?

Answer 19

Question 20

Name and describe how the glucogenic amino aicds contribute to the TCA cycle.

Answer 20

carbons of these amino acids can be used in gluconeogenesis:

Thr, Gly, Trp, Ala, Ser, Cys, Asp, Asn, Tyr, Phe, Val, Ile, Met, Arg, His, Gln, Pro

Question 21

Identify and describe how the ketogenic amino acids feed into the TCA.

Answer 21

ketogenic amino acids made acetyl CoA or acetoacetate:

Trp, Thr, Lys, Ile, Leu, Tyr, Phe

Question 22

asparagine to oxaloacetate

Answer 22

Question 23

a-KG from glutamine

Answer 23

Question 24

a-KG from proline

Answer 24

type I hyperprolinemia - defect in proline dehydrogenase

typw II hyperprolinemia - defect in glutamate semialdehyde dehydrogenase

Question 25

a-KG from arginine

Answer 25

hyperarginemia - defect in arginase gyrate atrophy of the choroid and retina - mutations in ornithine-aminotransferase

Question 26

a-KG from histidine

Answer 26

glutamate formimino transferase uses folate, so deficiency will cause high levels of Figlu

Question 27

pyruvate from alanine

Answer 27

Question 28

pyruvate from serine

Answer 28

Question 29

pyruvate from cystine and cysteine

Answer 29

cystine is a dimer of cysteine PAPS is used as a sulfate donor for the synthesis of sulfated proteoglycans

Question 30

propionyl CoA from methionine and threonine

Answer 30

propionyl CoA can feed into the TCA cycle through conversion to succinyl CoA S-adenosyl-L-methionine is important in single carbon transfer reactions

Question 31

propionyl CoA by valine and isoleucine

Answer 31

oxidative decarboxylation by branched-chain alpha-keto acid dehydrogenase complex deficincies in this enzyme result in maple syrup urine disease caused by accumulatiuon of branched-chain alpha-keto acids in theurine, giving it a sweet odor occurs primarily in peripheral tissues and not liver

Question 32

acetyl-CoA and acetoacetate from leucine

Answer 32

blockage of enzyme also causes maple syrup uring disease also occurs primarily in peripheral tissues instead of liver

Question 33

acetyl-CoA from tryptophan

Answer 33

first step of the process requires vitamin B6

Question 34

fumarate, acetyl CoA and acetate from tyrosine

Answer 34

type II tyrosinemia, neonatal tyrosinemia, alkaptonuria, type I tyrosinemia

Question 35

lysine degradation

Answer 35

produces a dicarboxylic acid which can undergo beta-oxidation

Question 36

synthesis of non-essential amino acids

Answer 36

asparagine, aspartate, glycine, serine, cysteine, alanine, glutamate, glutamine, proline, arginine

Question 37

serine from glycolysis intermediates

Answer 37

Question 38

glycine from serine

Answer 38

folate as cofactor major reaction is serine to glycine

Question 39

cysteine from serine and methionine

Answer 39

Question 40

proline from glutamate

Answer 40

glutamate semialdehyde dehydrogense is important

Question 41

synthesis and degradation of spartate and asparagine

Answer 41

Question 42

tyrosine from phenylalanine

Answer 42

phenylketonuria is a disease due to deficiency in phenylalanine hydroxylase leads to alternative pathways which give urine particular odor

Question 43

nucleoside

Answer 43

base with sugar

Question 44

nucleotide

Answer 44

phosphorylated nucleoside

Question 45

purine biosynthesis frome ribose 5-phosphate

Answer 45

requires folic acid first reaction is important R5P comes from PPP end result is inosine monophosphate

Question 46

AMP and GMP from IMP

Answer 46

Question 47

Describe the regulation of de novo purine nucleotide biosynthesis.

Answer 47

AMP, GMP, ADP, and GDP all regulate the intial steps of purine biosynthesis

Question 48

Describe the regulation involved in balancing ATP and GTP levels

Answer 48

Question 49

salvage of purine bases

Answer 49

Lesch-Nyhan syndrome - complete deficiency of HGPRT, unable to salvage hypoxanthine or guanine leads to productio of excess uric acid HGPRT = hypoxanthine-guanine phosphoribosyl transferase

Question 50

biosynthesis of pyrimidines

Answer 50

starts from glutamine and CO2, ends up as UDP, which can be converted into TMP or CTP folate is a carbon donor

Question 51

interregulation of nucleotides

Answer 51

Question 52

synthesis of deoxyribonucleotides

Answer 52

maintains a blance of deoxyribonucleotides for DNA synthesis high ATP levels can cause problems if not regulated such as in immunodeficiency disease as the result of an adenine deaminase deficiency

Question 53

degradation of purines

Answer 53

occurs in cells of intestinal mucosal cells of the small intestine with uric acid as the final product gout - caused by high levels of uric acid in the blood, resulting in the deposition of monosodium urate in the joints allopurinol can be used to treat by decreasing rate of degradation

Question 54

degradation of pyrimidines

Answer 54

eventually converted to succinyl CoA

Question 55

tetrahydrofolate (FH4)

Answer 55

the main coenzyme in accepting one carbon groups, once one-carbon groups reduced to methyl, carbon cannot be re-oxidized have to get folate from diet

Question 56

sources of one-carbon groups

Answer 56

serine, glycine, formaldehyde, histidine, formate

Question 57

dTMP from dUMP

Answer 57

transfer of a one-carbon unit, uses TH4 cancer treatment dugs 5-fluorocuracil and methotrexate interfere with this pathway to kill dividing cells

Question 58

viatmin B12 (cobalamin

Answer 58

involved in transfer of methyl group to homocysteine to form methionine also involved in rearrangement of L-methylmalonyl CoA to form succinyl CoA

Question 59

S-adenosylmethionine (SAM) from methionine

Answer 59

SAM is a major methyl donor for formation of methylated histones methionine obtained from diet or produced from homocysteine

Question 60

The Methyl-Trap Hypothesis

Answer 60

vitamin B12 is required to take methyl group from FH4, if deficient for vitamin B12 or if methionine synthase is defective, the N5-methyl-Fh4 will accumulate and most of the folate in the body becomes trapped there, creating a functional folate deficiency