Amino Acid Degradation/Urea Cycle

Question 1

What is secreted by parietal cells in the stomach?

Answer 1

HCl

Question 2

What is secreted by chief cells in the stomach?

Answer 2

Pepsinogen

Question 3

What class of enzyme is pepsinogen?

Answer 3

zymogen

Question 4

What is the active form of pepsinogen?

Answer 4

pepsin

Question 5

What changes pepsinogen into its active form pepsin?

Answer 5

low pH

Question 6

What does pepsin do?

Answer 6

Acts as an endopeptidase, cleaving peptide bonds to form smaller peptides and some free aa

Question 7

What side group does pepsin prefer?

Answer 7

CO group provided by an aromatic or acidic amino acid

Question 8

Where are pancreatic zymogens activated??

Answer 8

small intestine

Question 9

What cellular mechanism absorbs amino acids?

Answer 9

Na+ transport proteins

Question 10

What disease is characterized by an inability to absorb amino acids in the kidney due to defective Na+ amino acid pumps?

Answer 10

Hartnup disease

Question 11

Why do patients with hartnup disease often show symptoms of pellagra?

Answer 11

Because they can’t absorb normal amounts of tryptophan, which is a precursor for niacin synthesis.

Question 12

Patients with Cystinuria have problems absorbing which amino acid?

Answer 12

Cystine

Question 13

What molecule tags proteins for degradation intracellularly?

Answer 13

ubiquitin

Question 14

What protein degrades proteins inside the cell tagged by ubiquitin?

Answer 14

26S proteasome

Question 15

Besides in the cytosol with proteasomes, where can proteins be degraded in the cell?

Answer 15

lysosomes

Question 16

What type of enzymes degrade proteins in lysosomes and what is their optimal pH?

Answer 16

acid hydrolases

pH 5

Question 17

What are two examples of enzymes that degrade proteins extracellularly?

Answer 17

Serine proteases
matrix metalloproteases (Ex collagenases)

Question 18

Where does the urea cycle take place?

Answer 18

Liver

Question 19

What is the only organ with all of the enzymes for urea synthesis?

Answer 19

Liver

Question 20

Which is very toxic to the CNS, ammonia or ammonium ion?

Answer 20

ammonia (in equilibrium with ammonium ion)

Question 21

What are the two nontoxic compounds that ammonia is converted to?

Answer 21

Urea and glutamine

Question 22

What are the two types of reactions used to remove the amino groups in amino acid catabolism?

Answer 22

Transamination and deamination

Question 23

What type of reaction moves amino groups into glutamate?

Answer 23

Transamination

Question 24

What type of reaction directly releases ammonium ions?

Answer 24

Deamination

Question 25

What type of enzymes catalyze the transfer of an alpha-amino group from an amino acid to an alpha-ketoacid during transamination?

Answer 25

Aminotransferases (transaminases)

Question 26

Serum levels of what two amino acid transferases are used to evaluate liver damage?

Answer 26

``` Aspartate aminotransferase (AST) Alanine aminotransferase (ALT) ```

Question 27

What cofactor is required for aminotransferase reactions?

Answer 27

pyridoxal phosphate (PLP)

Question 28

What vitamin is PLP derived from?

Answer 28

B6

Question 29

Are transamination reactions reversible?

Answer 29

Yes

Question 30

What are the three types of deamination reactions?

Answer 30

Oxidative Deamination Hydrolytic Deamination Nonoxidative deamination

Question 31

Which deamination reaction is PLP dependent?

Answer 31

nonoxidative deamination

Question 32

Oxidative deamination is a reaction in liver mitochondria and is catalyzed by what enzyme?

Answer 32

glutamate dehydrogenase

Question 33

What two side aa side chain groups are targeted by hydrolytic deamination?

Answer 33

glutamine and asparagine

Question 34

What is an important deamination reaction in the kidney?

Answer 34

hydrolytic damination of glutamine by glutaminase

Question 35

What two amino acid side chains undergo nonoxidative damination?

Answer 35

Serine | Threonine

Question 36

What are the enzymes of the two major nonoxidative damination reactions?

Answer 36

serine dehydratase threonine dehydratase *both use PLP prosthetic group*

Question 37

What molecules transport most nitrogen from other tissues to liver or kidney?

Answer 37

Alanine | Glutamine

Question 38

Glutamine synthetase is one of three human enzymes that can fix ____ in a carbon compound

Answer 38

NH4+

Question 39

Why do mutations in glutamine synthetase cause severe brain malformation is newborns?

Answer 39

Glutamate is a neural toxin, large amounts of it accumulate in the brain

Question 40

What conditions would produce a postive-nitrogen balance in a patient? Need to increase protein synthesis

Answer 40

Physical trauma Growing child excreted N < consumed N

Question 41

What conditions would produce a negative-nitrogen balance in a patient? Body protein degraded to synthesis essential proteins

Answer 41

protein malnutrition or starvation | excreted N > consumed N

Question 42

What is the expectation of most all urea cycle defects?

Answer 42

hyperammonemia | There is no other way to get rid of NH4+

Question 43

What enzyme is involved in the rate limiting step of the urea cycle?

Answer 43

Carbamoyl phosphate synthetase 1 (CPS 1)

Question 44

Where is CPS1 located?

Answer 44

mitochondria

Question 45

What does CPS require as a cofactor?

Answer 45

N-acetylglutamate (NAG) | *allosteric activator*

Question 46

Where is NAG synthesized?

Answer 46

Mitochondria by N-acetylglutamate synthase

Question 47

NAG synthase is positively regulated by the presence of?

Answer 47

Argenine

Question 48

Which form of CPS 1 is active? the dimer or the monomer?

Answer 48

monomer

Question 49

What does CPS1 reaction require?

Answer 49

2 ATP | NH3 from deamination rxns

Question 50

What molecule is the first and last step of urea synthesis?

Answer 50

Ornithine