Nitrogen Turnover

Question 1

nitrogen compoounds are degraded into mostly

Answer 1

• urea

- urea levels are the only thing that changes in excretion with regards to proteins intake

Question 2

excretion in urine comes in four forms

Answer 2

• ammonia
• urea
• uric acid (purine breakdown product)
• creatinine (proportional to muscle mass)

Question 3

balance of nitrogen in the body

Answer 3

• intake from protein in the diet
• goes into amino acid pool and can then be used for body protein or made into urea and excreted
• if you are in a positive balance you will have more going to body protein than you are excreting
• during times of insufficient protein, you have more going back into the amino acid pool from the body protein and that is being made into urea

Question 4

tramua and urea balance

Answer 4

• high energy requirement

- a lot more going into the amino acid pool and being made into urea

Question 5

what are the 3 steps of removin nitrogen

Answer 5

• transfer to a common carrier
• ammonia is regenerated in the liver
• ammonia is incoporated into urea

Question 6

what is a common carrier of nitrogen

Answer 6

-alpha ketogluterate which then turns into glutamate

Question 7

PLP

Answer 7

• is used by aminotransferase in order to transfer a nitrogen from an amino acid a common carrier
• arises from VB6
• exhanges a keto group fro a amine group

Question 8

glutamate dehydrogenase

• location
• function
• what happens to its product in the liver
• cofactors

Answer 8

• this is located in the mitochondria and is fundamental for the release of ammonia so it can be acted on by CPSI to create carbamoyl phsophate for the urea cycle
• in liver, the ammonia produced can be incorporated into urea
• urea production is significant only in the liver
• uses NAD or NADP as cofactors

Question 9

regulation of glutamate dehydrogenase

Answer 9

• activity increased by ADP and GDP

- activity decreased by ATP and GTP

Question 10

what is ammonia produced from on asparagine and glutamine

Answer 10

-amide groups

Question 11

minor way to dispose of ammonia

Answer 11

• make glutamate by running the glutamate dehydrogenase reaction in reverse
• this is when the urea cycle is saturated

Question 12

major way of disposing of ammonia

Answer 12

• make glutamine via the glutamine synthase reaction
• used to fix ammonia especially in the brain; also occurs in muscle, lungs, and adipose tissue
• glutamine is a majr carrier of n in the blood
• glutamine levels increase after a protein rich meal

Question 13

problem with hyperammonemia in children

Answer 13

• glutamate can only hold so much ammonia as glutamine before it maxes out and the body runs out of glutamine
• when this happens, hyperammonemia will present and this can cause serious health problem (especially in the brain)

Question 14

urea cycle order and mnemonic

Answer 14

• ordinarily careless crappers are also frivolous about urination
• ornithing, carbamoyl phosphate, citrulline, aspartate, arginosuccinate, fumarate, arginine, urea

Question 15

CPSI

Answer 15

• founds in the mitochondria
• needs NAG to function
• NAG is made by NAG synthase using acetyl-CoA and glutamate
• NAG synthase uses arginine
• produces carbamoyl phosphate from NH4 which comes from the glutaminase and glutamate DH reactions

Question 16

how is Nag synthase deficiency treated?

Answer 16

with carbamoyl glutamate

Question 17

what does a deficiency in any of the urea cycle enymes result in?

Answer 17

-elevated ammonia

Question 18

where do the two nitrogens that make up urea come from?

Answer 18

aspartate and NH4 from carbamoyl phosphate

Question 19

how many ATPs are used to make urea

Answer 19

4

Question 20

clinical symptoms of a inoperative or stressed urea cycle -

Answer 20

• developmental delays
• cognitive delays
• seizure
• protein intolerance

Question 21

diagnosing urea cycle defs

Answer 21

• blood/urine amino acids analyses for ammonia

- enzyme assay

Question 22

treatment of yrea cycle disorders

Answer 22

• restrict proteins from diet, this lowers nitrogen production
• supplement with arginine
• increase nitrogen excretion using benzoate or pheylacetate or phenylbutyrate

Question 23

how does the urea cycle interact with carb metabolism

Answer 23

• argininosuccinate is converted into fumerate using argininosuccinase
• fumerate can then be converted into OAA for gluconeogenesis, or into malate for pyruvate/PEP or sent to the mitochondria to directly aparticipate in the TCA

Question 24

why might we need to replenish ornithine or arginine and how do we do so

Answer 24

-ornithin can be used to make polyamine (spermine)
-arginine is used to make NO which is a vasodilator
-glutamine can be used to make glutamic semialdehyde which can be converted into ornithine
glutamic semialdehyde can also be made from ornithine which can then be used to make proline