Carbon Skeletons Khan

Question 1

468. What is the only tissue that has all the pathways for amino acid synthesis and degradation?

Answer 1

468. Liver

Question 2

469. What are all 20 AA’s able be broken down into?

Answer 2

469. AcetylCoA, pyruvate, 4 TCA intermediates (OAA, fumarate, succinylCoA, alphaketoglutarate)

Question 3

470. What is a ketogenic AA?

Answer 3

470. Can be made into AcetylCoA or acetoacetate

Question 4

471. What is a glucogenic AA?

Answer 4

471. Can be made into glucose

Question 5

472. What are the purely ketogenic AA’s?

Answer 5

472. Leucine/Lysine

Question 6

473. What are the ketogenic/glucogenic AA’s?

Answer 6

473. Phe/Tyr, Ile, Trp

Question 7

474. Describe the pathway of glycine synthesis

Answer 7

474. Pyruvate –> serine –> glycine via PLP and THF –> Gly

Question 8

475. During glycine synthesis what is a methyl group transferred to that can form carbon dioxide
     and ammonium ion?

Answer 8

475. THF

Question 9

476. By enzymatic action of an oxidase what can glycine become?

Answer 9

476. Glyoxylate

Question 10

477. What is the condition caused by defective transaminase in Gly metabolism?

Answer 10

477. Oxaluria type I (due to less conversion of glyoxylate back to Gly and accumulation of
     glyoxylate)

Question 11

478. What is a clinical condition manifested by excess glyoxylate

Answer 11

478. kidney stones (ppt. with calcium)

Question 12

479. Degradation of what other AA other than Ser can generate Gly?

Answer 12

479. Thr

Question 13

480. In cysteine metabolism where does the sulfur originally come from?

Answer 13

480. Met

Question 14

481. Met is degraded to generate what product (via methyltransferase)

Answer 14

481. Homocysteine

Question 15

482. What intermediate is used in Met degradation for methyl transfer?

Answer 15

482. SAM

Question 16

483. What can homocysteine be then converted into?

Answer 16

483. Back to Met or into cysteine via cystathionase

Question 17

484. What can cysteine be degraded to?

Answer 17

484. Sulfinic acid, in presence of alpha ketoglutarate it can be degraded to pyruvate (thus it
     is a glucogenic AA)

Question 18

485. The sulfhydryl groups of cysteine can be oxidized to form what which generate sulfated
     proteoglycans

Answer 18

485. PAPs

Question 19

486. Can cysteine inhibit cystathione synthase via feedback inhibition?

Answer 19

486. Yes

Question 20

487. What does a deficiency in cystathionase lead to?

Answer 20

487. Cystathionuria (benign disorder)

Question 21

488. What could cause a deficiency in cystathione?

Answer 21

488. Dietary deficiency of pyridoxine(Vit. B6) or Vit. B12

Question 22

489. What does a deficiency in cystathionine synthase cause?

Answer 22

489. Homocystinemia/Homocystinuria (accumulation of homocysteine and met in brain,
     can cause loss in cognitive fx. , tall stature, CV disease, thrombi, emboli, etc.)

Question 23

490. What is the treatment for homocystinuria?

Answer 23

490. Low met diet, high doses of pyridoxine

Question 24

491. Can our bodies synthesize aromatic rings?

Answer 24

491. No (makes them essential AA’s)

Question 25

492. How is tyrosine synthesized?

Answer 25

492. From Phe via hydroxylation reaction using oxygen and tetrahydrobiopterin

Question 26

493. T or F: Any defective step in Phe or Tyr synthesis causes severe diseases

Answer 26

493. T

Question 27

494. What does a deficiency in Phe hydroxylase present as?

Answer 27

494. Phenylketouia (PKU), phenylpyruvate accumulates and is excreted (mental retardation, lighter skin due to impaired tyrosine synthesis)

Question 28

495. What is the treatment for PKU?

Answer 28

495. Diet low in Phe, rich in Tyr

Question 29

496. What is the first step in degradation of tyrosine?

Answer 29

496. Removal of ammonia via tyrosine aminotransferase

Question 30

497. What does a defect in this step cause?

Answer 30

497. Tyrosinemia II (eye, skin, lesions, neurological disorders)low tyr and low phe diet is treatment

Question 31

498. What does deficiency in homogentisate oxidase cause?

Answer 31

498. Alcaptonuria (accumulation of homogentisate which causes arthritis)

Question 32

499. What does a deficiency in degradation of fumarylacetoacetate cause?

Answer 32

499. Tyrosinemia I (liver failure and death within 1 yr of life)

Question 33

500. Where does the aromatic ring of Trp end up via degradation pathways?

Answer 33

500. NAD/NADP

Question 34

501. Where does the carbon skeleton of Trp end up?

Answer 34

501. Ala

Question 35

502. Trp to NAD requires what cofactor? What does a deficiency in this cofactor cause?

Answer 35

502. PLP, pellagra like symptoms

Question 36

503. What are the branched chain AA’s?

Answer 36

503. Val, Ile, Leu

Question 37

504. What can these AA’s generate via transamination rxn?

Answer 37

504. Alphaketovalerate, alpha keto beta methylvalerate, alphaketoisocaproate

Question 38

505. What are branched chain AA’s ultimately converted to?

Answer 38

505. propionylCoa or Acetyl CoA

Question 39

506. What is homocistinuria type 1 caused by?

Answer 39

506. cystathionine synthase deficiency (high homocystine and methionine levels)

Question 40

507. What is homocystinuria type 2/3 caused by?

Answer 40

507. deficiency in methl‐b‐12 and methyl THF synthesis (high serum homocysteine and low methionine levels)