Semester 2: Amino acids and nucleotide metabolism

Question 1

What does a negative nitrogen balance mean?

Answer 1

• Excreted nitrogen > ingested nitrogen (starvation, diseases)

Question 2

What does a positive nitrogen balance mean?

Answer 2

• Ingested nitrogen > excreted nitrogen (children, pregnancy)

Question 3

What is transamination?

Answer 3

A reversible exchange of an amino- and an oxo group (alpha-AA –> alpha-keto acid)

Question 4

ALAT

Answer 4

• Ala aminotransferase
• Ala -> Pyruvate
• Alpha-KG -> Glutamate
• PLP prostetic group
• Liver

Question 5

ASAT

Answer 5

• Asp aminotransferase
• Oxa -> Asp
• Alpha-KG -> Glutamate
• PLP prostetic group
• Heart/muscle

Question 6

GLUD1

Answer 6

• Glutamate dehydrogenase isoenzyme used in oxidative deamintaion
• Found in liver, kidney and other tissues
• Allosterically inhibited by: ATP, GTP, NADH
• Activated by ADP

Question 7

GLUD2

Answer 7

• Glutamate dehydrogenase isoenzyme used in oxidative deamintaion
• Found in brain, testis

Question 8

What is the purpose of urea cycle?

Answer 8

Excretion of amino group and free ammonia

Question 9

Allosteric activation of CP synthetase

Answer 9

Presence of N-acetyl-glu (from acetyl-CoA and glutamate)

Question 10

Hyperammonemia type 1

Answer 10

alpha-KG is used for removal of ammonia, therefore the citrate cycle is depleted: Low ATP level -> coma
- Type 1: CP synthetase I deficiency -> Arg supplementation

Question 11

Hyperammonemia type 2

Answer 11

• Ornithine transcarbamoylase def. –> mental retardation
• Arginosuccinate synthetase def. -> citrullinemia (Arg supplement)
• Arginosuccinate lyase def. -> arginosuccinate secretion (Arg supplement)
• Arginase def. -> high Arg level (Arg-free diet)

Question 12

Succinyl-CoA forming AAs

Answer 12

Ser, Cys, Thr, Val, Ile

Question 13

Pyruvate forming AAs

Answer 13

Ala, Ser, Gly

Question 14

Alpha-ketoglutarate forming AAs

Answer 14

Pro, Glu, Gln, Arg, (orn)

Question 15

Amino acids involved with H4F derivatives

Answer 15

His, Trp, Ser, Gly

Question 16

Glutamate dehydrogenase reaction

Answer 16

• alpha-KG + NH4 + NADPH –> Glu + NADP + H2O

- Glu + NADP + H2O –> alpha-KG + NADPH + NH4

Question 17

Carbamoyl p synthetase I

Answer 17

NH4 + Bicarbonate + 2ATP -> Carbamoyl-P + 2ADP+Pi

Question 18

Ornithine transcarbamoylase

Answer 18

Carbamoyl-p + Ornithine -> Citrulline

Question 19

Arginosuccinate synthetase

Answer 19

Citrulline + Asp + ATP -> Arginosuccinate + AMP+PPi

Question 20

Arginosuccinate lyase

Answer 20

Arginosuccinate -> Arg

+Fumarate

Question 21

Arginase

Answer 21

Arg -> Urea (+ornithine)

Question 22

Serine dehydratase

Answer 22

Ser -> aminoacrylate -> pyruvate + NH4

- Coenzyme: PLP

Question 23

Thr dehydratase

Answer 23

Thr -> alpha-ketobutyrate

- Coenzyme: PLP

Question 24

Gln synthetase

Answer 24

Glu + NH4 + ATP -> Gln + ADP+Pi

Question 25

Asn synthetase

Answer 25

Gln + Asp + ATP -> Glu + Asn + AMP+PPi

Question 26

Folate consist of

Answer 26

Pterin, para-aminobenzoic acid, glutamic acid

Question 27

DHFR

Answer 27

H2F + NADPH -> H4F + NADP

Question 28

MTHFR

Answer 28

CH2-H4F + NADH -> CH3-H4F + NAD

Question 29

Homocysteine methyltransferase

Answer 29

- CH3-H4F -> H4F - HomoCys -> Met - Prostethic group: B12

Question 30

Met adenosyl transferase

Answer 30

Met + ATP -> SAM + PPi+Pi

Question 31

SAM dependent methylase

Answer 31

SAM -> SAH + CH3

Question 32

SAH hydrolase

Answer 32

SAH -> HomoCys + adenosine

Question 33

Cystationine synthase

Answer 33

- PLP + Vit B6 | - Ser + Met -> custathione -> Cys + alpha-ketobutyrate

Question 34

Alpha-ketobutyrate DEH complex

Answer 34

Alpha-ketobutyrate + NAD -> propionyl-CoA + NADH

Question 35

Propionyl-CoA carboxylase

Answer 35

- Biotin | - Propionyl-CoA + ATP -> Methylmalonyl-CoA + ADP+Pi

Question 36

Methylmalonyl CoA racemase + methylmalonyl-CoA mutase

Answer 36

- B12 | Methylmalonyl CoA -> Succinyl CoA

Question 37

Maple syrup urine disease

Answer 37

Deficiency of BCKD (branched chain alpha-ketoacid dehydrogenase) - ketoacidosis, mental retardation

Question 38

Asparaginase

Answer 38

Asn -> Asp + NH4+

Question 39

Glutamate decarboxylase

Answer 39

Glu -> GABA + CO2

Question 40

PRPP synthetase

Answer 40

R-5-P + ATP -> PRPP + ADP

Question 41

AMP deaminase

Answer 41

AMP + H2O -> IMP + NH4+

Question 42

Adenylosuccinate synthase

Answer 42

IMP + Asp + GTP -> Adenylosuccinate + GDP + Pi

Question 43

IMP dehydrogenase

Answer 43

IMP + H2O + NAD -> XMP + NADH

Question 44

GMP synthase

Answer 44

XMP + Gln + ATP -> GMP + ADP+Pi + Glu

Question 45

Purine salvage reaction enzymes

Answer 45

- Adenine phsophoribosyl transferase (adenine->AMP, PRPP->PPi) - Hypoxanthine guanine phosphoribosyl transferase

Question 46

Catabolism of purine nucleotides, enzymes

Answer 46

- 5´nucleotidase (AMP-> adenosine) | - Purine nucleoside phosphorylase

Question 47

Hyperuricemia (gout)

Answer 47

Causes: - PRPP overproduction (PRPP synthase mut.) - Overproduction of R-5-P - Absence of purine salvage reactions (eg. HPRT def.) - Low ATP level, disturbed ATP metabolism Medication: Allopurinol

Question 48

Orotic aciduria

Answer 48

Causes: - UMP-S def. - Inhib. of UMP-S - Ornithine transcarbamoylase def.

Question 49

Pyrimidine salvage reaction enzyme

Answer 49

Uridine kinase, cytidine kinase

Question 50

Thymidylate synthase

Answer 50

dUMP -> dTMP | - Inhibited by 5F-dUMP (colon cancer)