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Biochemistry II > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

How are dietary proteins broken down?

A

Proteases hydrolyze them into free amino acids, dipeptides, and tripeptides

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2
Q

What are essential amino acids? Which ones are they?

A

Essential amino acids are those that must be acquired from the diet because an organism is unable to synthesize them.

TV FILM HW(R*)K

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3
Q

What is the primary protease of the stomach?

A

Pepsin; it is a nonspecific protease

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4
Q

Where are MOST digestive enzymes synthesized, and how are they released?

A

Most digestive enzymes are synthesized in the pancreas, and they are secreted into the intestine as zymogens

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5
Q

What is aminopeptidase?

A

It is a nonspecific protease that hydrolyzes proteins from the amino terminal end

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6
Q

The half life of proteins varies. How is the half life of proteins determined?

A

The N-terminal sequence determines the half life

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7
Q

Which amino acids on the N terminal favor ubiquitination (fast destruction)?

A

Arginine and Leucine

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8
Q

Which amino acids on the N terminal disfavor ubiquitination (slow destruction)?

A

Methionine and Proline; these amino acids signal a long half life

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9
Q

How are proteins marked for degradation?

A

Polyubiquitination; ubiquitin (Ub) forms polymers; it is the “mark of death” for proteins

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10
Q

How is ubiquitin covalently attached to proteins marked for destruction?

A

The C terminal glycine of Ub is attached to the epsilon amino group of lysine; all proteins have at least 1 lysine residue on their surface

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11
Q

Which 3 enzymes are involved in the attachment of Ub to proteins?

A

E1 or Ubiquitin-activating enzyme

E2 or Ubiquitin-conjugating enzyme

E3 or Ubiquitin-protein ligase

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12
Q

What does Ubiquitin-activating enzyme do?

A

It activates Ub by adenylation; it attaches the C terminal carboxylate of the activated Ub to itself via a thioester bond

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13
Q

What does Ubiquitin-conjugating enzyme do?

A

It transfers the activated Ub from a sulfhydryl of E1 to E2 (itself)

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14
Q

What does Ubiquitin-protein ligase do?

A

It transfers Ub from E2 to the target protein

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15
Q

What is the largest gene family in humans?

A

Ubiquitination enzymes

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16
Q

Which 3 diseases are linked to improper functioning of E3?

A

Some forms of Parkinson’s disease, Angelman syndrome, and HPV

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17
Q

Describe the structure of proteasomes

A

2 19S alpha caps
1 20S beta catalytic core
Has a total of 28 subunits

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18
Q

On which subunit of the proteasome is the active site located?

A

On the beta subunits within the 20S core; threonine residue acts as a nucleophile

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19
Q

What do proteasomes do?

A

Proteasomes hydrolyze ubiquitinated proteins

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20
Q

What is Bortezomib (Velcade)

A

It inhibits proteasomes; used as therapy for multiple myeloma

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21
Q

What are the primary and secondary sites of amino acid degradation?

A

The liver is primary; muscle is secondary, and degrades branches chain aa’s (L,I, V)

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22
Q

What are the 2 steps involved in amino acid degradation?

A
  1. Removal of a-amino group (it is transferred to a-KG)

2. Conversion of C-N to C=O (by glutamate DH)

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23
Q

What do aminotransferases use as their prosthetic group?

A

PLP from vitamin B6 (pyridoxine); they transfer a-amino groups from amino acids to a-KG to form glutamate

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24
Q

What does glutamate dehydrogenase do, and what is special about it?

A

Glutamate dehydrogenase converts nitrogen of glutamate to ketoacid and free ammonium ion; it can use EITHER NAD+ or NADP+

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25
Q

How are Schiff bases formed during amino acid degradation?

A

Pyridoxal phosphate forms the Schiff base; it can accept/ donate protons

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26
Q

Which two amino acids can be directly deaminated? And what are the products of these reactions?

A

Serine and threonine; they do not have to go through glutamate

Serine –> pyruvate + NH4+
Threonine –> a-ketobutyrate + NH4+

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27
Q

Which enzymes deaminate serine and threonine respectively, and how?

A

Serine dehydratase and threonine dehydratase;

Both enzymes dehydrate their substrates, and then re-hydrates them w/ the loss of the amino group

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28
Q

What is the alanine cycle? And where does it occur?

A

The alanine cycle occurs between muscle tissue and liver;

Branched chain amino acids are degraded and converted to alanine in muscle tissue

Alanine leaves the muscle and travels to the liver, where it is converted to pyruvate and glutamate.

Pyruvate can then be used in GN

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29
Q

What are ureotelic organisms?

A

Ones that excrete excess nitrogen in the form of urea; includes terrestrial vertebrates, like humans

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30
Q

Organisms that excrete excess nitrogen as uric acid are called?

A

Uricotelic; includes birds and reptiles

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31
Q

Aquatic organisms excrete excess nitrogen in the form of what?

A

Ammonium; they’re called ammonotelic

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32
Q

What is the urea cycle?

A

The synthesis of urea from carbamoyl phosphate and ornithine

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33
Q

Where do the atoms of urea come from?

A

1 nitrogen comes from ammonium

1 nitrogen comes from aspartate

1 Carbon comes from bicarbonate (dissolved CO2)

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34
Q

What enzyme synthesizes carbamoyl phosphate, and from what substrates?

A

Carbamoyl phosphate synthetase I; it is located in the mitochondrial matrix

It uses ammonia and bicarbonate

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35
Q

How many ATP are used in the synthesis of carbamoyl phosphate?

A

2 ATP/ 1 carbamoyl phosphate synthesized

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36
Q

What 3 sites are located on carbamoyl phosphate synthetase I?

A

Glutamine hydrolysis site (source of NH4+)

Bicarbonate phosphorylation site

Carbamic acid phosphorylation site

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37
Q

What is substrate channeling, and which 2 enzymes use this?

A

Substrates pass from one active site to another through a channel; not released by enzyme.

Used by carbamoyl phosphate synthetase 1 and in the synthesis of tryptophan (protects the indole group)

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38
Q

Name the 4 enzymes used in the urea cycle

A

Ornithine transcarbamoylase

Argininosuccinate synthetase

Argininosuccinate

Arginase

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39
Q

This enzyme catalyzes the synthesis of citrulline. What are its substrates?

A

Ornithine transcarbamoylase; it uses ornithine and carbamoyl phosphate

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40
Q

This enzyme condenses citrulline and aspartate to argininosuccinate

A

Argininosuccinate synthetase

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41
Q

This enzyme cleaves argininosuccinate into arginine and fumarate

A

Argininosuccinase

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42
Q

What does arginase do in the urea cycle?

A

It hydrolyzes arginine into ornithine and urea

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43
Q

What two intermediates link the urea cycle to gluconeogenesis?

A

Aspartate (can come from OAA) and fumarate (can be converted to malate, and then OAA)

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44
Q

What are hyperammonemias, and what can cause them?

A

Elevated level of ammonia in the blood; can be caused by lack/ reduced synthesis of carbamoyl phosphate or by lack/ reduced activity if one of the four enzymes of the urea cycle

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45
Q

Which amino acids are essential?

A

TV FILM HWK

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46
Q

Threonine can be degraded into pyruvate. What is the intermediate in this pathway?

A

2-amino-3-ketobutyrate (we just oxidized C3 from an alcohol to a carbonyl group)

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47
Q

What is the sulfur atom of cysteine converted to during catabolism?

A

It can be converted to H2S, SCN-, or SO32-

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48
Q

Branched chain amino acids, and aromatic amino acids can be broken down into what products?

A

Acetyl CoA and acetoacetyl CoA; note that HMG is an intermediate as well

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49
Q

What are oxygenases? They are required for the catabolism of which amino acids?

A

Oxygenases are enzymes involved in redox reactions; they’re required for the breakdown of aromatic amino acids (F, W, Y)

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50
Q

What is a monooxygenase? Give example

A

An enzyme capable of splitting a molecule of oxygen, in which each oxygen atom ends up in two different products;

Phenylalanine hydroxylase is a monooxygenase; oxygen ends up in Tyrosine and water

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51
Q

Which two pathways is phenylalanine hydroxylase involved in?

A

Conversion of Phe to Tyr

And the synthesis of Tetrahydrobiopterin (BH4) from phenylalanine

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52
Q

Which two other enzymes are involved in the synthesis of BH4, and what are their substrates?

What are their coenzymes?

A

Dihydrofolate reductase reduces dihydrobiopterin to BH4

Dihydropteridine reductase reduces quinoid dihydropterin to BH4

Both enzymes use NADPH

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53
Q

What are the two dioxygenases uses in the catabolism of Phe/ Tyr?

A

p-hydroxyphenylpyruvate hydroxylase AND homogentisate oxidase

Phe/ Tyr can be both glucogenic and ketogenic

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54
Q

What two products can tryptophan be broken down into?

A

Alanine and acetoacetate via both mono and dioxygenases

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55
Q

What is the product of destination of glutamate?

A

a-Ketoglutarate

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56
Q

What enzyme hydrolyzes the nitrogen of glutamine to glutamate?

A

Glutaminase

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57
Q

Which 2 amino acids from a glutamate gamma- semialdehyde intermediate during their catabolism?

A

Proline and arginine

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58
Q

A 4-imidazole-5-propionate intermediate is involved in the catabolism of which amino acid?

A

Histidine

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59
Q

The catabolism of some amino acids involve intermediates common to the oxidation of odd numbered fatty acids. What are they?

A

Propuinyl CoA
Methylmalonyl CoA
Succinyl CoA

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60
Q

The catabolism of methionine involves this intermediate, that acts as a methyl donor:

A

S-adenosylmethionine (SAM)

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61
Q

Serine and homocysteine combine to form:

A

Crystathionine, which is converted to a-ketobutyrate by removing cysteine

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62
Q

Which 4 enzymes are directly deaminated (amino group not transferred to glutamate)?

A

Serine, threonine, aspartate, and asparagine

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63
Q

Aspartate is directly deaminated to what?

A

OAA

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64
Q

What enzyme converts asparagine to aspartate by removing ammonium (side chain)

A

Asparaginase

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65
Q

What was the first description of an inborn error of metabolism?

Which amino acids aren’t degraded properly?

What intermediate accumulates as a result?

A

Alcaptonuria

Defective degradation of Phe/ Tyr

Homogentisate accumulates = black urine

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66
Q

What defect leads to maple syrup urine disease MSUD?

A

Defect in the degradation of branched-chain amino acids (muscle tissue) (Val, Ile, and Leu)

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67
Q

In MSUD, a-ketoacids in urine react with this molecule for detection:

A

2,4-dinitrophenylhydrazine

68
Q

What enzyme is defective/ missing in patients with phenylketonuria?

A

Phenylalanine hydroxylase; Phe accumulates (causing reactions) and Tyr isn’t synthesized

Phenylpyruvate in urine reacts w/ FeCl3, turning urine olive green

69
Q

What is the source of nitrogen for the synthesis of amino acids and nucleotides?

A

Nitrogen gas (N2), which is fixed/ reduced to ammonia mostly by diazotrophic microorganisms

70
Q

What does the Haber process require?

A

500 degrees Celsius, 300 atm pressure, and an iron catalyst. 25% of nitrogen fixation

71
Q

What two components make up the nitrogenase complex, and what do they do?

A

Reductase: transfers electrons (8) from reduced ferredoxin to nitrogenase complex

Nitrogenase: uses electrons from reductase to reduce nitrogen gas to ammonia

72
Q

Describe reductase (aka Fe protein) of the nitrogenase complex

A

Reductase has 4Fe-4S cluster; it is a dimer, and each subunit binds ATP (2/e- transferred), so they have P loops (NTPase family)

73
Q

What does reductase use to transfer electrons to nitrogenase?

A

The hydrolysis of ATP; 2 ATP are hydrolyzes per electron transferred

74
Q

Describe nitrogenase (aka MoFe protein) of the nitrogenase complex

A

MoFe = molybdenum iron cofactor

A2B2 tetramer

P cluster (stores electrons before transfer)

Has 2 unique iron sulfur clusters:
M-3Fe-3S, in which M = Mo in one cluster, and M= Fe in the other cluster

75
Q

Which orientation are the amino acids in our bodies?

A

In the L orientation

76
Q

What reaction does glutamate dehydrogenase catalyze in the catabolism and the anabolism of amino acids?

A

Anabolism: the synthesis of glutamate from ammonium and a-KG and NADPH

Catabolism: converts a-amino group of glutamate to C=O; NH4+ is a byproduct

Glutamate dehydrogenase can use either form of NAD+/ NADP+ in its reactions

77
Q

What are the common features of amino acid synthesis?

A

There is some activated intermediated;

A Schiff base is formed, followed by protonation, and reduction

78
Q

When is the stereochemistry of all chiral amino acids established?

A

In the second step of glutamate dehydrogenase mechanism, in which the protonated Schiff base accepts a hydride from NADPH

79
Q

What enzyme synthesizes glutamine, and how is the precursor activated?

A

Glutamine synthetase; it uses ATP to phosphorylate glutamate. Then the phosphate group is displaced by ammonia

80
Q

Synthesis of aspartate:

Enzyme and precursor

A

Aspartate transaminase transfers ammonium from glutamate to OAA to make aspartate

81
Q

Alanine synthesis enzyme and precursor?

A

Alanine transaminase transfer ammonium from glutamate to pyruvate to make alanine

82
Q

Synthesis of asparagine: enzyme and precursor. What is special about the precursor?

A

Asparagine synthetase uses glutamine ** (NH4+ donor) and aspartate to make asparagine

83
Q

Asparagine synthetase and glutamine synthetase both use ATP, but how are they different?

A

Asparagine synthetase uses ATP to activate aspartate by adenylation

Glutamine synthetase uses ATP to activate glutamate by phosphorylation

84
Q

What serves as the precursor for the synthesis of proline, arginine, and ornithine? What happens?

A

Glutamate; glutamate is phosphorylated by ATP, then the carboxylate is reduced, forming an aldehyde (glutamic gamma-semialdehyde)

85
Q

Which intermediate is common in both the synthesis and degradation of the amino acids arginine and proline?

A

Glutamic gamma-semialdehyde

86
Q

What are the two precursors/ ways serine can be synthesized from?

A

3-phosphoglycerate (glycolytic intermediate) or glycine

87
Q

How is serine synthesized from 3-PG

A

First, the alpha hydroxyl group of 3-PG is oxidized to a carbonyl, forming 3-phosphohydroxy pyruvate

Then glutamate provides a-amino group, making 3-phosphoserine, which is then dephosphorylated to make serine

88
Q

Which two amino acids are in equilibrium in every cell? What does this mean?

A

Glycine and serine; it means they can be synthesized from each other

89
Q

In what 2 ways can glycine be synthesized?

A
  1. Serine hydroxymethyl transferase

2. Serine synthase (aka glycine cleavage enzyme)

90
Q

How is glycine made using serine hydroxymethyl transferase?

A

Serine HMT uses serine and THF to make glycine and methyl-THF

91
Q

How is glycine made using serine synthase?

A

Serine synthase uses ammonium, carbon dioxide, and N5N10-methylene-THF (cofactor) to make glycine and THF

92
Q

What is tetrahydrofolate?

A

THF is a cofactors that carries activated one carbon units, which may be attached to N5, N10, or both

Humans are not able to synthesize it (vitamin B9)

93
Q

Which enzymes use some form of THF?

A

Serine hydroxymethyl transferase Serine synthase

Dihydrofolate reductase

94
Q

What is SAM synthesized from? How many phosphate groups are retained?

A

Methionine and ATP

None

95
Q

What is the purpose of the activated methyl cycle?

A

To regenerate methionine from homocysteine

96
Q

How is homocysteine converted to methionine?

A

It is methylated

97
Q

What enzyme synthesizes methionine, and what does it require?

A

Methionine synthase (aka homocysteine methyltransferase)

It requires methyl cobalamin (B12)

98
Q

What are the two ways to get rid of homocysteine?

A

Synthesize methionine

Synthesize cysteine (serine + homocysteine)
* cystathionine is an intermediate
99
Q

What 2 enzymes are used to synthesize cysteine from homocysteine?

What does 1 use?

What are the substrates?

A

Cystathionine B- synthase (uses PLP, B6)

Cystathionase

Homocysteine + serine

  • Sulfur comes from homocysteine; carbon backbone comes from serine
100
Q

What is the most common cause of high homocysteine levels, and what does elevated levels cause?

A

A mutation in the cystathionine B-synthase enzyme

High levels lead to coronary heart disease

101
Q

How is high levels of serum homocysteine treated?

A

Vitamins:

B12 and THF required for methionine synthase

B6 required for cystathionine B-synthase

102
Q

How is tyrosine synthesized?

A

From Phe via phenylalanine hydroxylase (a monooxygenase that requires BH4- an electron carrier)

103
Q

Phenylalanine, tyrosine, and tryptophan are synthesized in bacteria. Which intermediates are used, and what pathways do they come from?

A

PEP (from glycolysis)

Erythrose-4P (from PPP)

104
Q

What are two intermediates in the synthesis of the aromatic amino acids? Which one is the last common intermediate?

A

Shikimate and Chorismate

Chorismate is the last common intermediate

105
Q

What is the chemical name for Roundup, and what pathway does it inhibit?

A

Glyphosate

It inhibits synthesis of aromatic amino acids

106
Q

From Chorismate, how are phenylalanine and tyrosine synthesized?

A

Chorismate –> phenylpyruvate –> phenylalanine

Chorismate –> p-hydroxyphenylpyruvate –> tyrosine

107
Q

How is the indole group of tryptophan incorporated? Where does tryptophan’s amino group come from?

A

The indole group is combined with serine, which provides tryptophan w/ an amino group

108
Q

Which two amino acids do NOT get their a-amino group from glutamate?

A

Arginine (from glutamine)

Tryptophan (from serine)

109
Q

What is PRPP involved in?

A

PRPP = activated ribose

The synthesis of the amino acid tryptophan and the synthesis of nucleotides

110
Q

When is substrate channeling used?

A

In the synthesis of tryptophan and the synthesis of carbamoyl phosphate

111
Q

What is negative nitrogen balance?

A

More proteins are broken down than synthesized.

Occurs when there is an amino acid deficiency

112
Q

All aminotransferases contain which 2 conserved amino acids? What do they do?

A

Lysine (forms Schiff base w/ PLP)

Arginine (interacts w/ alpha carbonyl of ketoacid)

113
Q

Nitric acid (NO) is synthesized from what amino acid?

A

Arginine

114
Q

What are the precursor amino acids for glutathione?

A

Glutamate
Cysteine
Glycine

(ECG)

115
Q

Porphyrins are used to synthesize what molecule? And what are the precursors of porphyrins?

A

Heme;

Glycine and succinyl CoA

116
Q

What does glutathione reductase do?

A

Reduces GSSG to GSH; used NADPH and FAD

117
Q

What does glutathione peroxidase do?

A

It reduces hydrogen peroxide to water; a selenium ion replaces the sulfur of a cysteine residue in the active site

118
Q

What enzyme catalyzes the synthesis of nitric oxide? What are the substrates?

A

Nitric oxide synthase; it uses arginine, NADPH and molecular oxygen (O2)

119
Q

What does nitric oxide do?

A

It functions as a smooth muscle dilator and as a messenger in signal transduction pathways

120
Q

What are porphyrins?

Which one is heme?

A

Porphyrins are cyclic compounds that readily bind metal ions

Protoporphyrin IX = Heme

121
Q

Where in the cell is heme synthesized? Which tissues/ cells carry out heme synthesis?

A

Heme synthesis occurs in the mitochondria and the cytoplasm

Erythrocyte-producing cells of bone marrow and hepatic cells carry out heme synthesis

122
Q

What is ferrochelatase?

A

An enzyme that enhances the rate of addition of iron

123
Q

What is ferritin?

A

An iron storage protein

124
Q

What is transferrin?

A

Iron transport protein

125
Q

What are porphyrias?

A

Autosomal dominant disorders caused by deficiency of enzymes in the heme biosynthetic pathway

126
Q

How is bilirubin made? What enzyme? Where is bilirubin broken down?

A

The enzyme bilirubin reductase synthesizes bilirubin from the reduction of biliverdin (a linear tetrapyrrole)

Bilirubin is broken down in the liver

127
Q

What are the two sources of nucleotide synthesis?

A

Salvage pathways (bases are recovered and attached to PRPP)

De novo synthesis

128
Q

What is the difference between pyrimidine synthesis and purine synthesis?

A

Pyrimidines are synthesized FIRST, and then attached to ribose

Purines are synthesized WHILE attached to ribose

129
Q

What is the final step in the synthesis of thymine?

A

Methylation of uracil

130
Q

What are deoxyribonucleotides synthesized from?

A

Ribonucleotides

131
Q

What kind of base are xanthine and inosine?

A

They are purines

132
Q

What are the sources of the atoms of the pyrimidine ring?

A

Carbamoyl phosphate (N3, and C2)

Aspartate (N1, C4,5,6)

133
Q

Carbamoyl phosphate synthetase synthesizes carbamoyl phosphate. What is the difference in CPS I and CPS II?

A

CPS I is used for the urea cycle, and thus is only found in the liver

CPS II is used in nucleotide biosynthesis, and this is found in all cells

134
Q

What reaction does dihydrorotase catalyze?

A

The synthesis of dihydroorotate through hydrolytic cyclization

135
Q

What does pyrimidine phosphoribosyl do in nucleotide biosynthesis?

A

It attaches orotate (pyrimidine) to ribose (PRPP)

136
Q

What does dihydroorotate dehydrogenase do?

A

It catalyzes oxidation of the ring, converting dihydroorotate to orotate

137
Q

What does orotidylate decarboxylase do?

A

Converts orotidylate (OMP) to uridylate (UMP)

138
Q

What is the reaction of nucleotide diphosphate kinase?

A

NDP + XTP –> NTP + XDP

139
Q

What enzyme catalyzes the synthesis of CTP? From what? How?

A

CTP synthetase (uses ATP)

From UTP

By animation of the keto group on C4; the amino group comes from the R group of Glutamine

140
Q

What enzyme catalyzes the synthesis of TMP? From what? How?

A

Thymidylate synthase

From dUMP !! Produces dUMP

The prosthetic group of thymidylate synthase (N5,N10-methylene-THF) donates one carbon and two hydrogens

During the reaction, THF is converted to DHF

141
Q

What molecule inhibits thymidylate synthase? How?

A

Fluorouracil; it is a nucleotide analog; competes for active site; suicide inhibitor

142
Q

What enzyme catalyzes the reduction of DHF to THF? What drugs inhibit it? How?

A

Dihydrofolate reductase

Inhibited by aminoptrin and methotrexate; both are competitive inhibitors

143
Q

What is methotrexate?

A

A competitive inhibitor; will INDIRECTLY inhibit ANY drug that uses THF as a prosthetic group, because it prevents the synthesis of THF from DHF

144
Q

PRPP is used in the synthesis of what molecules?

A

Nucleotides and histidine

145
Q

What is the last common intermediate of purine synthesis?

A

Inosine (IMP)

146
Q

In purine synthesis, the activation of a carbonyl by phosphorylation is common. Which molecules are activated like this?

A

Glycine and bicarbonate

147
Q

Purine synthesis: Glutamine phosphoribosyl amidotransferase

A

The snide group of glutamine replaces the pyrophosphate group on C1 of ribose

(PRPP + NH4+ –> phosphoribosyl amine

148
Q

What enzyme does IMP inhibit?

A

Glutamine phosphoribosyl amidotransferase

149
Q

What does pyrophosphorylase do?

A

Hydrolyze pyrophosphate to provide energy

150
Q

Phosphoribosyl amine combines with this amino acid to form ?

A

It combines w/ glycine

They form glycinamide ribonucleotide

151
Q

Formyl transferase enzymes appear twice in purine synthesis. What is its prosthetic group, and what does it carry?

A

THF is the PG, and it adds formal groups (aldehyde) to nitrogen atoms

152
Q

What type of enzyme catalyzes the formation of an amidine group? Where does the amino group come from?

A

A synthetase is used

The amino group comes from glutamine

Glutamine donates an amino group to convert the carbonyl into an amidine group

153
Q

There are 2 ring closing reactions in purine synthesis. Which enzymes catalyze them?

Which ring is synthesized first?

A

A synthetase first closes the imidazole ring

Then a cyclohydrolase closes the pyrimidine ring through (dehydration)

154
Q

In purine synthesis, this step is not catalyzes by an enzyme. How does it happen?

A

The carbon dioxide (from bicarbonate) jumps from N3 to C5, becoming C6

This reaction is under equilibrium control; no enzyme used

155
Q

Purine synthesis: when step is fumarate lost in?

A
  1. Adenylsuccinate lyase, in which a C-N bond is cleaved
156
Q

Which enzyme catalyzes the formation of the last common intermediate (IMP) of purine synthesis?

A

Cyclohydrolase

157
Q

What enzyme synthesis AMP from IMP? Where does the amino group come from?

A

Adenylosuccinats synthetase; amino group comes from aspartate

158
Q

What enzyme catalyzes the synthesis of GMP from IMP? How?

A

GMP synthetase

Inosinate is oxidized to xanthylate (using NAD+)

The keto group of Xanthylate is then aminated (NH4+ from Glu) to form Guanylate (GMP)

159
Q

What enzyme converts ribonucleotides into deoxribonucleotides? How?

A

Ribonucleotide reductase reduces the 2’ hydroxyl to a hydrogen

It uses NADPH

160
Q

What order are dNTPs synthesized in?

A

First, nucleotide monophosphates are made

Then, they are phosphorylated to nucleotide diphosphates

Lastly, ribonucleotide reductase is used to convert rNDPs into dNDPs

dNTPs are made by further synthesis from nucleoside diphosphate kinase

161
Q

How are purines catabolized? What is the final product?

A

Both AMP and GMP are converted into xanthine

Xanthine is converted to urate, which is excreted in the urine

Hydrogen peroxide is formed in this catabolism, and must be degraded

162
Q

What is urate?

A

Product of purine catabolism; it is a powerful scavenger of ROS

163
Q

Which amino acid is the precursor of sphingosine?

A

Serine

164
Q

Which amino acid is the precursor of histamine? How?

A

Histidine

Decarboxylation

165
Q

Which amino acid is the precursor of of epinephrine, melanin, and thyroxine?

A

Tyrosine

166
Q

Which amino acid is the precursor of serotonin?

A

Tryptophan

167
Q

Which amino acid is the nicotine mode ring of NAD+ synthesized from?

A

Tryptophan

Biochemistry II (2 decks)

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