Urea Cycle

Question 1

________ is a chemical reaction between two molecules. One is an amino acid, which contains an amine (NH2) group. The other is a keto acid, which contains a keto (=O) group.

Answer 1

Transamination

Question 2

______ is the removal of an amine group from a molecule. Enzymes that catalyse this reaction are called deaminases

Answer 2

deamination

Question 3

____ is deaminated in the kidneys, but the majority of things are deaminated in the ______

Answer 3

glutamate, liver

Question 4

over 90% of nitrogen excretion is in the form of ______

Answer 4

urea

Question 5

________ is the degradation product of purine bases

Answer 5

uric acid

Question 6

list four purine bases

Answer 6

adenine, guanine, hypoxanthine and xanthine

Question 7

______ is released from glutamate, especially by the _____

Answer 7

ammonia, kidneys

Question 8

NH3

Answer 8

ammonia

Question 9

____ is a very important ion for pH control and buffering of urine

Answer 9

ammoium ions (NH4+)

Question 10

transamination rxns are catalyzed by transaminsases, aka ______

Answer 10

aminotransferases

Question 11

_____ is an enzyme that catalyzes a type of reaction between an amino acid and an α-keto acid.

Answer 11

transaminases/aminotransferases

Question 12

what is the major cofactor for transamination rxns?

Answer 12

pyridoxal phosphate

Question 13

what are the 3 transamination pairs?

Answer 13

asparate & oxaloacetate,
glutamate & alpha-ketoglutarate,
alanine & pyruvate

Question 14

pyridoxal phosphate (PLP) is derived from _______

Answer 14

Pyridoxine (vit B6)

Question 15

all AA except what 3 can undergo transamination?

Answer 15

lysine, threonine, proline

Question 16

for almost all reactions the ____________ pair serves as one of the alpha-keto AA pairs

Answer 16

alpha-keotglutarate - glutamate

Question 17

is transamination reversible?

Answer 17

yes

Question 18

____ is the transaminase that present in the cytoplasm of liver cells

Answer 18

alanin transaminase (ALT) aka as glutamic pyruvic transaminase - GPT

Question 19

____ is the transaminase that present in liver, heart, and skeletal muscle

Answer 19

aspartate transaminase (AST) aka as glutamic oxalacetic transaminase-GOT

Question 20

damage to specific organs will result in an increase of serum levels of what?

Answer 20

ALT and AST (corresponding to the organ)

Question 21

describe the first rxn of the urea cycle

Answer 21

ammonium ions (NH4+) are rapidly converted to carbomoyl phosphate, this occurs in the mitochondria

Question 22

what are the allosteric inhibitor of glutamate dehydrogenase (GDH) for oxidative deamination

Answer 22

high ATP, GTP, and NADH

Question 23

what is glutamate dehydrogenase?

Answer 23

it is an enzyme that catalyzes oxidate deamination between glutamate and alpha-ketoglutarate, which releases ammonium

Question 24

which amino acid is known as the “gate-way” amino acid and why?

Answer 24

glutamate, it always serves as one of the amino acids in transaminations

Question 25

where does oxidative deaminatio by L-amino acid oxidase mainly occur?

Answer 25

in the liver and kidneys

Question 26

what cofactor is needed for oxidative deaminatio by L-amino acid oxidase?

Answer 26

FMN (flavin mononucleotide)

Question 27

ammonium ions produced by non-oxidative deamination in non-hepatic tissues are transported to the liver in the form of what 3 possible things?

Answer 27

glutamate, glutamine, or alanine

Question 28

name the non-oxidative dehydration enzymes

Answer 28

Serine dehydratase, Threonine dehydratase, D-cysteine desulfhydrase

Question 29

name the non-oxidative hydrolytic enzymes

Answer 29

Glutaminase & Asparaginase

Question 30

Free ammonium ions in nonhepatic tissue are primarily detoxified by what enzyme?

Answer 30

glutamine synthetase

Question 31

glutamine synthetase make glutamine which then carries free ammonium ions to the liver for final conversion to what?

Answer 31

urea

Question 32

what enzyme is especially important in the kidney whose main function is the production of ammonia for acid-base regulation

Answer 32

glutaminase

Question 33

______ is a major amino acid of circulation; its role is to ferry ammonia to and from various tissues

Answer 33

glutamine

Question 34

In kidney, glutamine is hydrolyzed by ______ releasing the ammonia to the urine

Answer 34

glutaminase

Question 35

when does the liver divert ammonia to glutamine, then the kidney converts to a-ketoglutarate yields 2 NH4+ which reduces the H+ concentration.

Answer 35

under acidotic conditions

Question 36

(T/F) Humans are totally dependent on other organisms for converting atmospheric nitrogen into forms available to the body

Answer 36

true

Question 37

what is the primary source of nitrogen metabolized by the body?

Answer 37

dietary proteins

Question 38

is ATP required for the urea cycle?

Answer 38

yes

Question 39

where does the formation of carbamoyl phosphate occur?

Answer 39

the mitochondria

Question 40

how many nitrogens does aspartate provide?

Answer 40

one

Question 41

____ is released from arginine in a reaction catalyzed by _____

Answer 41

urea, arginase

Question 42

In the liver, the ammonia produced from what 3 things is converted to urea through urea cycle?

Answer 42

Glutamate, from AMP, or by direct deamination

Question 43

Carbon dioxide and ammonium ion react with two molecules of ATP to form _____

Answer 43

carbamoyl phosphate

Question 44

what 3 things react to form carbomoyl phosphate?

Answer 44

Carbon dioxide and ammonium ion react with two molecules of ATP

Question 45

____ or _____ can serve as the cofactor for glutamate dehydrogenase (GDH)

Answer 45

NAD+ or NADP+

Question 46

CPS1

Answer 46

Carbamoyl phosphate synthetase

Question 47

in the 2nd rxn of the urea cycle, Carbamoyl phosphate reacts with ______ to form ______, which moves out of the mitochondrion into the cytoplasm.

Answer 47

ornithine, citrulline

Question 48

what are 2 major promoters of the urea cycle?

Answer 48

NH4+ and glutamate

Question 49

the ctivation of carbamoyl phosphate synthetase I (CPSI) requires what precursors?

Answer 49

glutamate and acetyl CoA react with arginine to for N-acetyl glutamate

Question 50

describe the second rxn in the urea cycle

Answer 50

carbamoyl phosphate and ornithine are catalyzed by ornithine transcarbamoylase to form citrulline

Question 51

describe the 3rd rxn of the urea cycle

Answer 51

citrulline and aspartic acid are catalyzed by arginosuccinate synthetase to form arginosuccinate

Question 52

where do the rxns 3-5 of the urea cycle take place?

Answer 52

in the cytoplasm

Question 53

describe the 4th rxn of the urea cycle

Answer 53

arginosuccinate is catalyzed by arginosuccinate lyase to form arginine and fumurate

Question 54

describe the 5th and last rxn of the urea cycle

Answer 54

arginine is gatalyzed by arginase to form ornithine and urea

Question 55

Carbamoyl phosphate synthetase (CPS) is dependent on ________ for activity

Answer 55

N-acetylglutamate

Question 56

Synthesis of N-acetylglutamate is catalyzed by _________

Answer 56

N-acetylglutamate synthetase

Question 57

_____ is an allosteric activator of N-acetylglutamate synthetase

Answer 57

Arginine

Question 58

Defects in urea cycle result in what?

Answer 58

accumulation of ammonia in the blood

Question 59

All of the deficiencies of components needed for the urea cycle may present with _______

Answer 59

hyperammonemia

Question 60

define hyperammonemia

Answer 60

a metabolic disturbance characterised by an excess of ammonia in the blood

Question 61

brain damage, coma, and death due to lack of ATP, neural defects, and the depletion of glutamate stores needed to make GABA (the neurotransmitter) are all results of what?

Answer 61

ammonia intoxification

Question 62

(T/F) glutumate can readily cross the BBB

Answer 62

False, it cannot cross the BBB

Question 63

what are the 3 possible Tx's for defects in the urea cycle enzymes?

Answer 63

limit protein intake, remove excess ammonia, and replace missing intermediates from the cycle

Question 64

what two things can be used to remove excess ammonia from the blood stream?

Answer 64

sodium benzoate and sodium phenylacetate to bind up glycine and glutamine

Question 65

To Tx defects in the urea cycle enzymes you can replace the missing intermediate with ______ or_______

Answer 65

arginine or citrulline

Question 66

in the kidneys and more acidic condition _____ breakdown of glutamine and a less acidic condition ____ the breakdown

Answer 66

increase, decrease

Question 67

Kidneys and intestines jointly produce _______

Answer 67

arginine

Question 68

Massive resection of the small intestine can cause patients to become ______ deficient

Answer 68

arginine

Question 69

intestinal CPS1 and OTC form ______ which is exported into the blood and taken up by the kidneys to for arginine

Answer 69

citrulline

Question 70

____________ is the major process for removing nitrogen from amino acids

Answer 70

transaminase rxn

Question 71

deamination or serine, glutamate dehydrogenase reactions, bacteria in the instestinallumen, and glutaminase reactions are all sources of_____

Answer 71

ammonium (NH4+)

Question 72

what are the 4 main products of nitrogen metabolism?

Answer 72

urea, ammonia, creatinine, and uric aicd

Question 73

______ is the mechanism for continuously supplying tissues that use glucose as primary energy source during fasting, exercise etc.

Answer 73

the alanine cycle

Question 74

in the alanine cycle the generation of amino nitrogen requires how many ATP's for the disposal as urea?

Answer 74

4