Nitrogen Metabolism

Question 1

What is needed for the protein to be recognized for degradation by the proteasome complex?

Answer 1

The protein must be polyubiquitinated (attached by a bunch of lysines). After the protein goes through the complex, the lysine bonds are cleaved and the ubiquitin is reused.

Question 2

Proteolysis

Answer 2

hydrolytic cleavage of proteins in the stomach by proteases

Question 3

Carboxypeptidases and aminopeptidases

Answer 3

Carboxypeptidases clip proteins from the carboxyl end

Aminopeptidases clip proteins from the amino end

Question 4

Zymogens

Answer 4

Inactive proteolytic enzymes. Made in the pancreas

Question 5

Steps of the amino group from the amino acid

Answer 5

1. Transamination (amino group is transferred to alpha-ketoglutarate to form L-glutamate)
2. oxidative deamination (amino group is cleaved off to form toxic ammonium)
3. Urea Cycle

Question 6

2 amino acids that do not undergo a transamination reaction for degradation

Answer 6

Lysine and threonine

Question 7

Aminotransferase

Answer 7

Enzyme used in transamination reaction. Also use PLP

Question 8

3 amino acid-keto pairings

Answer 8

1. Glutamate/alpha-ketoglutarate (alanine transaminase)
2. Pyruvate/alanine (alanine transaminase)
3. Aspartate/oxaloacetate (aspartate transaminase)

Question 9

Where does oxidative deamination take place?

Answer 9

Mitochondria

Question 10

L-Glutamate dehydrogenase (Glu DH)

Answer 10

Enzyme used in oxidative deamination. Proton acceptor is NAD(P)+

Question 11

Allosteric modulators of Glu DH

Answer 11

Activator: ADP
Inhibitor: GTP

Question 12

Ammonia produced in non-liver tissues returns to the liver to enter the urea cycle in 2 ways

Answer 12

1. Glu is converted to Gln for safe, non-toxic transport. Enzyme is glutamine synthetase. Cleaved in the liver by glutaminase
2. (in muscles): Glucose-Alanine cycle adds amino group to pyruvate to from alanine, which can be safely transported in the blood to the liver

Question 13

Precursors of urea

Answer 13

NH4+, CO2, and aspartate

Question 14

location of the three reactions involved in the urea cycle

Answer 14

1st 2 reactions: mitochondrion

3rd reaction: cytosol

Question 15

What is the rate limiting step in urea biosynthesis?

Answer 15

Production of Carbamoyl Phosphate, because it requires two molecules of ATP (catalyzed by carbamoyl phosphate synthetase 1; requires N-acetylglutamate to be activated)

Question 16

Connection point between TCA cycle and Urea Cycle

Answer 16

Fumarate (second connection point is aspartate)

Question 17

Arginase

Answer 17

Cleaves off urea from arginine to form the beginning molecule ornithine

Question 18

Hyperammonemia

Answer 18

High levels of ammonia in the blood causes the body to synthesize glutamine from glutamate, leading to high levels of glutamine and low levels of glutamate. Both are problematic. Can result from liver damage or genetic problems

Question 19

Exclusively ketogenic amino acids

Answer 19

Lysine and leucine

Question 20

Glucogenic amino acids

Answer 20

Catabolized to either pyruvate or a TCA intermediate to make glucose

Question 21

Ketogenic amino acids

Answer 21

Catabolized to make acetyl CoA or acetoacetate and lead to the formation of ketone bodies, fatty acids, or their precursors

Question 22

Amino Acids that are both ketogenic and glucogenic

Answer 22

Tryptophan, Tyrosine, Phenylalanine, Isoleucine, and Threonine

Question 23

Maple syrup urine disease

Answer 23

Defective Branched Chain Alpha-Keto Acid dehydrogenase complex; leads to a buildup of alpha-keto acids in the body (fromed from leucine, isoleucine, and valine)

Question 24

Amino acids that form pyruvate

Answer 24

Trp–> Ala, Cys, Ser

Question 25

Amino acids that form oxaloacetate

Answer 25

Asn –> Asp

Question 26

Amino acids that form fumarate and Acetyl CoA

Answer 26

Phenylalanine –> Tyr

Question 27

Where are the carbons and nitrogens in porphyrins derived from?

Answer 27

Succinyl CoA and glycine

Question 28

Most common types of Porphyrias

Answer 28

1. Acute intermediate porphyria (requires environmental stimuli)
2. Porphyria cutanea tarda (like vampires)

Question 29

What amino acid are catcholamines synthesized from?

Answer 29

Tyrosine

Question 30

Which amino acid is the precursor to histamine?

Answer 30

Histidine (decarboxylation reaction)

Question 31

Which amino acid is serotonin and melatonin synthesized from?

Answer 31

Tryptophan

Question 32

Which amino acids are involved in the synthesis of creatine?

Answer 32

Methionine, glycine, and the guanidino group of Arg

Question 33

8 inhibitors of glutamine synthetase

Answer 33

AMP, CTP, His, Try, Carbamoyl phosphate, Glucosamine-6-phosphate, Gly, Ala

Question 34

S- adenosyl methionine (SAM)

Answer 34

donates a methyl group (eg. epinephrine synthesis)

Question 35

Glutamine amidotransferase

Answer 35

catalyzes the transfer of an amide group from glutamine

Question 36

Tetrahydrofolate (TH4) (folic acid)

Answer 36

different 1-C units:
CH3- methionine synthesis
CH2- serine synthesis
CHO- purine synthesis
CH= - TMP synthesis

Question 37

All amino acids are derived from intermediates of:

Answer 37

the pentose phosphate pathway, glycolysis, and the TCA cycle

Question 38

5 functions of nuceotides

Answer 38

1. precursors of DNA and RNA
2. ATP
3. part of 3 important coenzymes (NAD, FAD, CoA)
4. activated intermediates in many biosynthetic pathways
5. metabolic and physiologic regulators

Question 39

Two pathways of purine nucleotide synthesis

Answer 39

1. De novo pathway (from new)

2. Salvage pathway (reuse old pieces)

Question 40

Where does almost all of the ribose required for the purine nucleotides come from?

Answer 40

The pentose phosphate pathway

Question 41

5 phosphoribosyl 1 pyrophosphate (PRPP)

Answer 41

The activated form of ribose. Build purine rings onto inactive ribose rings

Question 42

Consume Gtp when you want to make an A containing compound

Answer 42

Consume an Atp when you want to make a G containing compound

Question 43

Regulation of Purine Nucleotide synthesis pathway

Answer 43

The nucleotides are inhibitors of their production pathways

Question 44

Inosinate (IMP)

Answer 44

branch point in purine biosynthesis

Question 45

ARPT and HGPRT

Answer 45

Enzymes involved in the salvage pathway. Can’t be reused/salvaged

Question 46

Lesch Nyhan Syndrome

Answer 46

genetic disorder that leads to reduced purine reutilization and increased purine production resulting in high uric acid levels

Question 47

4 steps of purine degradation

Answer 47

1. release purines
2. funnel into same pathway to make same purine derivative
3. convert to uric acid
4. excrete through urine

Question 48

De Novo pathway of pyrimidines

Answer 48

Only produce Uracil and Cytosine, not Thymine

1. create carbamoyl phosphate (rate limiting step catalyzed by CPS II)
2. build pyrimidine ring
3. link to ribose C1

Question 49

Inhibition of De Novo pyrimidine pathway

Answer 49

High levels of CTP

Question 50

Ribonucleotide reductase

Answer 50

Reduces RNA to DNA using NADPH
Inhibited by the DNA it produces, activated by the substrates
only works on diphosphates

Question 51

Does the De Novo pathway produce RNA or DNA?

Answer 51

RNA

Question 52

2 major protein degradation pathways

Answer 52

1. Ubiquitin-proteasome pathway

2. Chemical signals