Exam 2 Peng 2

Question 1

what are the two main ways to degrade AA?

Answer 1

1) transamination

2) oxidative deamination

Question 2

transamination is typically the first step in?

Answer 2

catabolism of AA

Question 3

is transamination reversible? catalyzed by?

Answer 3

Yes reversible; catalyzed by aminotransferase

Question 4

transamination produces?

Answer 4

glutamate

Question 5

What happens in transamination?

Answer 5

• *alpha-ketogluterate accepts the amino group from AA and becomes glutamate
• *AA loses amino group and becomes alpha-keto acid

Question 6

biological importance of transamination?

Answer 6

AA gives up amino group (CONTAINS NITROGEN) to form glutamate which is a common substrate! Now the body only needs ONE step oxidative deamination

Question 7

again, aminotransferases catalyze?

Answer 7

the transfer of alpha-amino groups to glutamate in transamination of AA; substrate specificity! many transfereases wont work on different AA

Question 8

what are the two most important aminotransferases?

Answer 8

1) asparate aminotransferase -asparate and alpha-ketogluterate= oxaloacetate and glutamate
2) alanina aminotransferase - alanine + alpha-gluatarate = pyruvate + glutamate

Question 9

What are good markers for liver diseases in the urine?

Answer 9

asparate aminotransferase and alanine aminotransferase because they are typically restricted to liver cells

Question 10

all aminotransferases require?

Answer 10

coenzyme pyridoxal phosphate

Question 11

what is coenzyme pyridoxal phosphate?

Answer 11

it is the coenzyme required by aminotransferase, derived off vitamin B6

Question 12

what is aminotransferases equilibrium constant? This means?

Answer 12

near 1. means it is HIGHLY reversible

Question 13

is oxidation deamination reversible? What type of reaction is it?

Answer 13

highly reversible; redox reaction (leo ger)

Question 14

what happens in oxidative deamination?

Answer 14

amino groups are liberates off glutamate as free ammonia; this is catalyzed by glutamate dehydrogenase mitochondrial enzyme

Question 15

what is oxidative deaminations coenzyme?

Answer 15

nicotinamide adenine dinucleotide

Question 16

what is nicotinamide adenine dinucleotide?

Answer 16

• the oxidator in oxidative deamination
• coenzyme for oxidative deamination
• phosphorylated and reduced form used in reversed rxn

Question 17

what is released in oxidative deamination?

Answer 17

NH3 which is turned into NH4 and converted to urea

Question 18

what is the issue with the creation of NH3 and NH4 in tissue other than the liver? how is this overcome?

Answer 18

it is toxic and must be kept at low levels in the blood. it is overcome y transporting nitrogen as alanine and glutamine in the blood, which are NON TOXIC

Question 19

how do you get alanine and glutamine as transporters?

Answer 19

1) glutamine cycle- glatamate combines with ammonia to form glutamine catalyzed by glutamine synthase
2) glucose alanine cycle- glucose is converted to pyruvate which is converted to alanine and released into blood
* *once glutamate and alanine reach the liver, they are deaminated down to ammonia again, peed out as uria

Question 20

what makes alanine and glutamine such good carriers of nitrogen?

Answer 20

muscles cells have lots of glucose to convert alanine and glutamine is literally glutamate with extra amine group

Question 21

what are the building blocks of urea?

Answer 21

C and O come from CO2 and water; one N from NH3 and the other from aspartate

Question 22

excess ammonium (NH4) is converted?

Answer 22

into urea by the urea cycle; major dispoal form of AA (90% of nitrogen in urine)

Question 23

urea is a nontoxic form of?

Answer 23

nitrogen

Question 24

sources of ammonia (NH3)?

Answer 24

1) AA deamination
2) plasma glutamine
3) bacterial action in the intestine (urease)
4) amines in the diet
5) catabolism of purines and pyrimidines

Question 25

where does glutamines formation from glutamate occur?

Answer 25

BRAIN, cns, liver, muscle

Question 26

glutamine is found where in higher concentrations than other AA?

Answer 26

plasma

Question 27

what is hyperammonenia?

Answer 27

elevated level of ammonia (NH3) in blood due to acquired liver disease or genetic defects in urea cycle
*if genetic= very fatal after 1 day of birth, treatment is protein restriction

Question 28

ammonia is especially toxic to?

Answer 28

CNS aka brain = coma or death

Question 29

with kidney failure, plasma urea increases through the action of?

Answer 29

intestinal bacteria urease leading to hyperammonia

Question 30

treatment of hyperammonia?

Answer 30

restiction of dietary protein

1) phenylacetate (binds and excretes glutamin)
2) antibiotics (suppress the action of intestinal bacteria urease)

Question 31

5 steps in urea cycle?

Answer 31

1) formation of carbamoyl phosphate from bicarbonate
2) formation of citrulline
3) synthesis of arginosuccinate
4) cleavage of arginiosuccinate
5) cleavage of arginine to ornithine and urea

Question 32

urea cycle is regulated by?

Answer 32

both substrate availbility and enzyme activity/availbility

Question 33

urea is transported from the liver? via?

Answer 33

liver to the kidney via blood and filtered and excreted in the urine

Question 34

where do the urea cycle steps occur?

Answer 34

1 and 2 in mitochondrial matrix, 3 in cytosol, 5 exclusively in liver

Question 35

what is stoichiometry of the urea cycle?

Answer 35

asparate +NH3+ HCO3+ 3ATP+ water –> urea, fumarate +2 ADP + AMP +2Pi + PPi (2 orthophosphate and 1 pyrophosphate)

Question 36

what steps in the urea cycle require energy?

Answer 36

1 uses 2 ATP and 3 uses 1 ATP

= 3 ATP total