Urea Cycle Khan

Question 1

426. What is the compound that is excreted containing nitrogen?

Answer 1

426. Urea

Question 2

427. What funnels amino groups into glutamate?

Answer 2

427. Transamination reactions

Question 3

428. Transamination moves an amino group from an AA to what?

Answer 3

428. Alpha keto acid

Question 4

429. What do all transaminases use to transfer amino groups?

Answer 4

429. Pyridoxyl 5’ phosphate (PLP)

Question 5

430. What does Ala + alphaketoglutarate produce via ALT ?

Answer 5

430. Pyruvate and glutamate

Question 6

431. What does glutamate and oxaloacetate produce via AST?

Answer 6

431. Alphaketoglutarate and aspartate

Question 7

432. If there is an abnormal increase in the substrates for these reactions (AST and ALT) what organ
     is in failure?

Answer 7

432. Liver

Question 8

433. What is an enzyme that uses NADPH to produce ammonia for the urea cycle?

Answer 8

433. Glutamate DH

Question 9

434. T or F: glutamate is a neurotransmitter

Answer 9

434. True

Question 10

435. What are Asn and Gln deaminated by and what do they form from these deaminations?

Answer 10

435. Asp, Glu via asparaginase and glutaminase

Question 11

436. What enzyme deaminates aspartate?

Answer 11

436. AST

Question 12

437. What do tumor cells require for growth that can be inhibited in these pathways?

Answer 12

437. Asparagine, inhibited by adding asparaginase which converts Asn to Asp

Question 13

438. What are Ser and Thr deaminated by?

Answer 13

438. Ser and Thr dehydratase to pyruvate & a‐ketobutyrate respectively

Question 14

439. What is the only form of nitrogen that can pass through membranes?

Answer 14

439. NH3

Question 15

440. What sites in the body is NH4+ released?

Answer 15

440. Liver and kidney

Question 16

441. If the liver is damaged would NH3 levels rise?

Answer 16

441. Yes without urea cycle it would accumulate

Question 17

442. How is urea in plasma measured?

Answer 17

442. Blood urea nitrogen (BUN), typically 8‐20mg/dl

Question 18

443. What can excess NH3 do to the body?

Answer 18

443. Ammonia can be made into glu which can deplete brain of alphaketoglutarate causing
     OAA to fall and TCA to stopcell dmg; increased Glu can lead to Gln formation which
     depletes Glu and GABA (NT’s); brain swelling due to osmotic pressure

Question 19

444. What enzyme in the Urea cycle adds nitrogen onto bicarbonate?

Answer 19

444. CPSI using ATP

Question 20

445. What enzyme adds carbomyl onto ornithine?

Answer 20

445. Ornithine transcarbamolase

Question 21

446. Where are the 2 enzymes aforementioned located?

Answer 21

446. Mitochondria

Question 22

447. What is the 3rd step in the urea cycle?

Answer 22

447. Arginnosuccinate synthetase to form Argininosuccinate from asprate and citrulline

Question 23

448. What is the 4th step?

Answer 23

448. Arginnosuccinase to cleave fumarate from argininosuccinate

Question 24

449. What is the 5th step?

Answer 24

449. Arginase to cleave urea off argininosuccinate and produce ornithine (cycle is complete)

Question 25

450. Where do steps 3‐5 take place?

Answer 25

450. Cytosol

Question 26

451. What is the overall reaction eqn. for urea cycle?

Answer 26

451. NH4+bicarbonate+amino group of Asp+ATPurea+fumarate+ADP+AMP+PPi

Question 27

452. How are the TCA and urea cycle linked?

Answer 27

452. Via fumarate and alphaketoglutarate

Question 28

453. How is most nitrogen carried in blood?

Answer 28

453. Glutamine

Question 29

454. Name two sources for NH3 in urea cycle

Answer 29

454. Glutamine via glutaminase, alanine via ALT

Question 30

455. What is the alanine cycle?

Answer 30

455. Glu in muscle transaminated to Ala which is transferred to liver and converted to pyruvate for further metabolism

Question 31

456. What type of hyperammonemia is genetic and most severe?

Answer 31

456. Type 1

Question 32

457. What type is late onset with liver cirrhosis?

Answer 32

457. Type 2

Question 33

458. What is an activator of CPS I?

Answer 33

458. N‐acetyl glutamate

Question 34

459. What synthesizes the answer to #458?

Answer 34

459. N‐acetyl glutamate synthetase (NAGS)

Question 35

460. What will a defect in NAGs lead to?

Answer 35

460. Type 1 hyperammonemia

Question 36

461. How can we treat hyperammonemia?

Answer 36

461. Benzoate, pheylacetateremoves gly and Gln causes cell to utilize NH3 to resynthesize them

Question 37

462. What are some characteristics of OTC deficiency?

Answer 37

462. Increased carbomoyl phosphate, increased orotic acid (via CPSII in purine synthesis)

Question 38

463. What is treatment for argininosuccinase deficiency?

Answer 38

463. Increased arginine, reduced protein intake

Question 39

464. What converts urea to carbonic acid and ammonia?

Answer 39

464. Urease generated by bacterium proteus mirabilis

Question 40

465. What is ppt’d as kidney stones?

Answer 40

465. Magnesium ammonium phosphate

Question 41

466. Where is the nitrogen in urea derived from?

Answer 41

466. Aspartate and ammonia

Question 42

467. What are some treatments for urea cycle deficiencies?

Answer 42

467. Low protein intake (replace with a‐ketoacids), remove excess ammonia by using levulose to kill ammonia producing bacteria, administer sodium benzoate,etc.