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M1 Biochemistry > Exam 2- Amino Acid Metabolism > Flashcards

Exam 2- Amino Acid Metabolism Flashcards

1
Q

Glucogenic amino acids

A

Metabolized to pyruvate, 3-phosphoglycerate, alpha-KG, OAA, fumarate, or Succinyl CoA

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2
Q

Ketogenic amino acids

A

Metabolized to acetyl CoA or acetoacetate

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3
Q

Essential amino acids

A

Amino acids that humans can’t synthesize
Pvt Tim Hall
Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine

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4
Q

Transamination reaction

A

An amino acid donates an amine group to a keto acid

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6
Q

Name the mandatory keto acid and an amino acid in the transamination reaction.

A

Alpha-ketoglutarate - mandatory keto acid

Glutamate - mandatory amino acid

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7
Q

Describe the role of pyridoxal phosphate (vitamin B6) in the transamination reaction.

A

Pyridoxal phosphate is the coenzyme involved in the transamination reaction.

In this reaction, the amine group is transferred from the amino acid to the coenzyme, which transports it to the alpha-keto acid, forming a new amino acid and regenerating the original coenzyme aldehyde.

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8
Q

Describe the role of glutamine with reference to nitrogen catabolism.

A

Glutamine is the transporter of excess nitrogen from the tissues to the liver for the Urea cycle

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9
Q

What are the substrates and products of carbamoyl phosphate synthase.

A

NH4 + HCO3- + 2 ATP —> Carbamoyl phosphate + 2 ADP + 2 Pi

Carbamoyl phosphate synthase I/CPS-1

N-acetylglutamate is a positive affector

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10
Q

Name two cellular compartments where the urea cycle operates.

A

Mitochondrial matrix and cytosol

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11
Q

Name the allosteric affector of carbamoyl phosphate synthase I

A

N-acetyl glutamate

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12
Q

Name a drug that is used for treatment of a urea cycle enzyme deficiency

A

Carbamoylglutamate - Analog of N-acetylglutamate, can also activate CPS-1

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13
Q

In an exercising muscle, name the cycle that utilizes an amino acid & converts it into glucose.

A

Glucose-Alanine Cycle

In the liver, alanine is converted to pyruvate by Alanine transaminase. When blood glucose is low, pyruvate —> GNG —> glucose!

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14
Q

Name 3 neurotransmitters that are derived from tyrosine

A

Dopamine

Epinephrine, norepinephrine

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15
Q

Name 3 types of reactions that are involved in producing a neurotransmitter from an amino acid precursor.

A

Decarboxylation
Hydroxylation
SAM-dependent methylation

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16
Q

Name 3 cathecholeamines

A

Dopamine
Norepinephrine
Epinephrine

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17
Q

Name the rate-limiting step in the biosynthesis of catecholeamines.

A

Tyrosine + O2 + THB —> DOPA + DHB

Tyrosine hydroxylase

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18
Q

Name the cofactors that is required for tyrosine hydroxylase.

A

Tetrahydrobiopterin

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19
Q

Catecholeamine release is stimulated by the neurotransmitter _____________

A

Acetylcholine

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20
Q

Name two enzymes that are involved in catecholeamine catabolism.

A

Catecholeamine O-methyltransferase (COMT)

Monoamine Oxidase (MAO)

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21
Q

Name few functions of catecholeamines.

A

To prepare the body for “fight or flight” response:

Increase cardiac output, glycogen degradation, triglyceride hydrolysis, and release of fatty acids from adipose tissue

Decrease peripheral resistance to blood flow.

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22
Q

Discuss the connection between Parkinson’s disease and dopamine and the drug that is used for patients.

A

Parkinson’s disease is due to a lack of dopamine synthesis. It can be treated by L-Dopa, a precursor of dopamine that can cross the blood-brain barrier.

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23
Q

Name 2 neurotransmitter compounds derived from tryptophan

A

Serotonin and melatonin

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24
Q

What is the hormone that is involved in circadian rhythms?

A

Melatonin

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25
Q

What is the effect of Prozac?

A

Inhibits reuptake process of serotonin

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26
Q

If you suffer from jet lag, what pathway would you target for drug therapy?

A

Melatonin

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27
Q

Name the enzyme that catalyzes the formation of histamines.

A

Histidine carboxylase

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28
Q

Name 3 functions of histamines

A

Mediate allergic and inflammatory reactions
Vasodilation & drop in BP
Constriction of bronchioles
Stimulates excretion of HCl

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29
Q

What are the substrates and products of glutamate decarboxylase?

A

Glutamate —> GABA
(E: glutamate decarboxylase)
Requires Pyridoxal Phosphate (vitamin B6)

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30
Q

In general, decarboxylases require the coenzyme _________

A

Pyridoxal phosphate

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31
Q

L-DOPA is used for ___________ disease treatment

A

Parkinson’s

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32
Q

Name a synthetic compound that limits serotonin reuptake.

A

Prozac

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33
Q

Describe pheochromocytoma.

A

Tumors of chromaffin tissue that produce large amounts of catecholeamines.

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34
Q

Describe the clinical correlation between Huntington’s disease and GABA metabolism.

A

Low levels of GABA and GABAnergic neurons result in the uncontrolled movements of Huntington’s disease

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35
Q

Melanins are synthesized in ___________

A

Melanocytes

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36
Q

Tyrosinase deficiency causes _____________

A

Albinism

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37
Q

Under oxidative conditions, in order to maintain reducing environment inside the cell, which compound is invoked?

A

Glutathione

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38
Q

Name the methyl group donor compound that is used in the majority of methyl transfer reactions

A

S-adenosylmethionine (SAM)

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39
Q

Name 2 functions of glutathione.

A

Maintains protein sulfuhydryl groups in reduced form.

Detoxifies xenobiotics (peroxides and free radicals) in the liver

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40
Q

Nitric oxide is derived from the amino acid _____________

A

Arginine

Uses THB

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41
Q

Name the substrate and products of acetylcholinesterase

A

ACh + H2O —> Acetate + Choline

E: Acetylcholine esterase

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42
Q

Explain the action of DIPF on acetylcholinesterase

A

DIPF is a component of nerve gas. It covalently modifies acetylcholinesterase and knocks the enzyme activity

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43
Q

Name some xenobiotics that inhibit acetylcholinesterase.

A

Physostigmine

Neostigmine

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44
Q

Name the channel that is opened up by acetylcholine.

A

Na+/K+ ion channels

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45
Q

Discuss the mechanism of action of nerve gas.

A

DIPF is a component of nerve gas. It covalently modifies acetylcholinesterase and knocks the enzyme activity.

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46
Q

Excitatory neurotransmitters

A

Excitatory:

  • Acetylcholine
  • Aspartate
  • Dopamine
  • Histamine
  • Norepinephrine
  • Epinephrine
  • Glutamate
  • 5-hydroxytryptamine
47
Q

Name Excitatory and Inhibitory neurotransmitters

A

Inhibitory:

  • Glycine
  • GABA
  • Taurine
  • 4-aminobutyrate

Excitatory:

  • Acetylcholine
  • Aspartate
  • Dopamine
  • Histamine
  • Norepinephrine
  • Epinephrine
  • Glutamate
  • 5-hydroxytryptamine
48
Q

Name the 3 stages of nerve transmission:

A

Resting
Excitation
Termination

49
Q

What is the action of GABA?

A

GABA is inhibitory neurotransmitter. Upon binding to its Beta subunits, it increases membrane permeability of postsynaptic membranes to chloride ion. This can lead to hyperpolarization and increased threshold of triggering an action potential.

50
Q

What is the function of phenobarbital?

A

Inhibits action potentials when bound to GABA receptors.

Tx for epilepsy

51
Q

Name the catabolic products of GABA.

A

Succinate semialdehyde

Succinate

52
Q

What is an ion-gated channel?

A

A channel that allows ions to pass through when a neurotransmitter binds to its receptor.

53
Q

Name 2 ion channels.

A

Cholinergic nicotinic receptors
GABA receptors
(More generally, Na and K channels)

54
Q

Diisopropylphosphoflouridate (DIPF) inhibits the enzyme ___________

A

Acetylcholinesterase

55
Q

Name two inhibitors of the ACh receptor

A

Tubocurarine
Alpha-bungarotoxin
Cobra toxin m

56
Q

Name two linear compounds in the proline biosynthetic pathway.

A

Glutamate and glutamate semialdehyde

57
Q

Describe the role of hydroxyprolines?

A

Collagen stability - stable collagen triple helix

58
Q

Name the amino acid that is required for selenocysteinyl tRNA synthesis.

A

Selenocysteine (21st amino acid)

59
Q

What is the cofactor that is required for phenylalanine hydroxylase synthesis?

A

Tetrahydrobiopterin (THB)

60
Q

What enzyme deficiency causes phenylketonuria?

A

Phenylalanine hydroxylase

61
Q

Name two disorders of tyrosine metabolism.

A

Alcaptonuria, Albinism.

62
Q

What enzyme deficiency causes albinism?

A

Tyrosinase

63
Q

Methionine adenosyltransferase catalyzes the synthesis of _______________

A

S-adenosylmethionine (SAM)

ATP —-> SAM (E: Methionine adenosyltransferase- MAT)

64
Q

What compound is the precursor for cysteine synthesis?

A

Methionine

65
Q

Name a disorder of cysteine metabolism.

A

Homocystinuria and Cystathionuria

66
Q

Name the oxidized form of homocysteine

A

Homocystine - consists of 2 molecules of homocysteine linked together by a disulfide bond

67
Q

Name the amino acid precursor for NMP synthesis

A

Tryptophan

Trp —> other steps —> —> niacin —> NMP

68
Q

Name an enzyme that requires a Vitamin B12 derivative as a coenzyme

A

Methionine synthase (in converting homocysteine to methionine)

Methyl Malonyl CoA Mutase (converting propionyl CoA to Succinyl CoA)

69
Q

Name a disorder of branched chain amino acid metabolism.

A

Maple syrup urine disease (MSUD)

70
Q

Name the amino acid that is required for carinitine biosynthesis.

A

Lysine

71
Q

Name two amino acids that are required for creatine biosynthesis.

A

Glycine and Arginine

72
Q

Name the components of folate.

A

Pterin, PABA, and Polyglutamine

73
Q

Name 2 active centers of THF.

A

N5 and N10

74
Q

Name the 3 reactions that use THF.

A

Purine synthesis
Thymidine synthesis
Methionine synthesis

75
Q

Name the amino acid and the vitamin derivative that is required for glycine synthesis.

A

Serine and THF

Serine + THF —> (E: Serinehydroxy methyl transferase) Glycine + N5-N10-Methylene THF

76
Q

Name two amino acid degradative pathways that require THF.

A

Histidine —> Glutamate

Serine —> Glycine

77
Q

Name two reactions that require Tetrahydrobiopterin as a cofactor.

A

Phenylalanine (Phenylalanine Hydroxylase) —> THB

Tyrosine (Tyrosine Hydroxylase) —> DOPA

Tryptophan (Tryoptophan Hydroxylase) —> Serotonin

78
Q

Describe how homocysteine is converted into methionine

A

Homocysteine —> methionine

Vit B12 derivative; E: Methionine synthase

79
Q

Lysine is required for the synthesis of _________

A

Carnitine

80
Q

Name the vitamin derivative that is required for the prolyl hydroxylase reaction.

A

Collagen

Vitamin C

81
Q

Why is the element selenium essential?

A

Activation of selenocysteine to tRNA

82
Q

Describe in detail the pathway of SAM and cysteine.

A

Methionine + ATP —> SAM —> Homocysteine (B6) —> Cystathione (B6) —> Cysteine + alpha ketobutyrate —> Propionyl CoA

83
Q

Biochemical basis of Phenylketonuria

A
  • Classical PKU is an autosomal recessive deficiency of phenylalanine hydroxylase
  • The accumulated phenylpyruvate and phenylketone are excrete in the urine
  • Since tyrosine production is affected, all the related compounds that are derived from tyrosine are also blocked (Ex. DA, NE/epinephrine)
  • In some individuals biopterin deficiency causes PKU
84
Q

Biochemical basis of Alkaptonuria

A
  • Deficiency of hemogentisate oxidase results in the accumulation of homogentisic acid
  • Upon accumulation, this compound is oxidized into a dark brown polymer and is deposited in joints, causing arthritis
85
Q

Biochemical Albinism

A
  • Tyrosinase deficiency results in defective melanin production
  • Skin is susceptible to the damaging effects of sunlight such as skin cancer
86
Q

The biochemical basis for Homocystinuria, Cystathionuria, Cystinuria

A

Issues with the cysteine biosynthetic pathway
- Vitamin B6 deficiency can block overall cysteine synthesis, as two steps in the pathway require B6 as cofactor

1) Homocystinuria:
- Cystathione beta-synthase deficiency causes homocysteine accumulation
- Vitamin B6 (pyridoxal phosphate) deficiency can exacerbate the condition

2) Cystathionuria:
- Gamma-cystathionase deficiency —> accumulated cystathionine for excretion
- Also requires Vitamin B6

3) Cystinuria
- Defect in membrane transport of dietary cysteine through epithelial cell membrane results in the accumulation of cysteine in the urine

87
Q

Maple syrup urine disease

A

Defect in catabolism of branched amino acids

Deficiency in branched chain keto acid dehydrogenase

88
Q

Histidinemia

A

Deficiency in the enzyme histidase

Histidine + THF —> Uroconate —> Glutamate

89
Q

Can folic acid be synthesized by humans?

A

No

90
Q

What step is inhibited by sulfamethoxazole?

A

Inhibits the conversion of para-amino benzocaine acid (PABA) —> folic acid

Folic acid synthesis is inhibited by sulfonamides

Only in prokaryotes

91
Q

The role of folate in relation to one carbon metabolism

A

Folate —> DHF —> THF (tetrahydrofolate)
With addition of a 1-carbon unit (tryptophan, hisitidine, serine/glycine) —> active folate

active folate —> purines, thymidine, and methionine

92
Q

Biosynthesis of carnitine

A

Lysine —> N-trimethyl lysine —> carnitine

E: Methyl transferase, 3SAM

93
Q

What are some organism specific dihydrofolate reductase inhibitors?

A

Methotrexate- eukaryotes
Epiroprim (type of trimethoprim)- bacteria
Pyrimethamine - protozoan (amoeba)

DHF (E: Dihydrofolate reductase) —> THF

94
Q

Trimethoprim, methotrexate, and pyrimethamine inhibits __________

A

They all inhibit Dihydrofolate reductase !

Methotrexate- eukaryotes
Epiroprim- bacteria
Pyrimethamine- protozoans/amoeba

95
Q

3 amino acid specific transaminase:

A 
Alanine aminotransferase (ALT): Alanine to pyruvate
Aspartate aminotransferase (AST): aspartate into OAA
Alpha KG —> Glutamate
96
Q

Name 3 glial cells and their functions n

A

Oligodendrocytes: provide mullein sheaths that insulinate axons

Astrocytes: integral parts of synapses, regulate molecules necessary for interneuron communication. Clear most of glutamate and stop neurotransmission. Also release growth factors and can take up other monoamine nt’s (serotonin and dopamine)

Microglia: closely related to macrophages, fight infections, and release inflammatory substances (may damage neurons) in response to injury

97
Q

ACh is not metabolized by reuptake process. Explain which cell would catabolize the ACh after the action potential.

A

Astrocytes

98
Q

Explain the differences between endogenous proteolysis (protein degradation) versus digestion related degradation.

A

Endogenous proteolysis = ubiquitination —> degradation by proteasome

Digestion related (dietary protein in excess) = proteolysis into amino acids which undergo transamination reactions producing nitrogen. Nitrogen taken to liver by glutamine, and nitrogen are fed into urea cycle and excreted

99
Q

Normal blood creatine levels

A

< 1.5 mg/dL

100
Q

Describe the lactate dehydrogenase catalyzed reaction.

A

Cori Cycle:

Muscle: Pyruvate —> Lactate (E: LDH-M)
Liver: Lactate —> Pyruvate (E: LDL-L) —> glucose (through GNG)
Glucose then transferred back to the muscle

101
Q

When lactate accumulates in the blood it is a problem. Why?

A

This can lead to lactic acidosis, which can cause a decrease in pH and muscle weakness

102
Q

Explain why vitamin B6 deficiency can cause brain related problems.

A

Glutamate —> GABA

Other reactions that use B6:
Histidine —> Histamine 
Dopa —> Dopamine 
Trp —> Serotonin 
Homocysteine —> Cystathione —> Cysteine
103
Q

Reactions that use THB

A

Phenylalanine —> Tyrosine
Tyrosine —> Dopa
Trp —> Serotonin
Arginine —> NO

104
Q

Describe the biosynthesis of creatine phosphate and its degradation.

A

Synthesis:
Glycine + Arginine (SAM) —> creatine phosphate (E: creatine kinase)

Degradation:
Creatine Phosphate —> (spontaneous!) creatinine —> excreted through urine!

105
Q

Which vitamin derivative is required for many of the decarboxylases?

A

Pyridoxal phosphate

106
Q

Describe the 3 NO synthases

A

Endothelium derived: diffuse out of endothelial cells into vascular smooth muscle, activates cytosolic guanylate cyclase which increases cGMP which up regulates PKG —> phosphorylation of smooth muscle contractile proteins leading to relaxation of vascular smooth muscles (vasodilation)

Brain derived:
Receptors for NO in neurons upregulate cytosolic guanylate cyclase increases cGMP which upregulates PKG —> phosphorylates proteins (not well understood)

Macrophage derived:
Stimulated after bacterial infection, NO toxic to bacteria

107
Q

Biochemical basis for Parkinson’s

A

Substantial Nigeria degraded —> decreased dopamine

108
Q

Biochemical basis for depression

A

Increased serotonin uptake and degradation (less serotonin)

109
Q

Pheochromocytomas

A

Tumors that increase production of catecholeamines —> HTN

110
Q

Huntington’s

A

Low GABA (inhibitory) leading to uncontrolled movements (chorea)

111
Q

Normal BUN levels

A

10-20 mg/dL

112
Q

Glucose-Alanine Cycle

A

In low oxygen conditions, alanine is transferred from the muscle to the liver
Alanine is converted to Pyruvate by alanine deaminase in the liver
Pyruvate can then re-enter the GNG cycle
Glucose returned to the muscle

113
Q

Describe the connection between dicarboxylate and the urea cycle

A

Fumarate leaves the Urea cycle in the arginosuccinate lyase step which converts arginosuccinate to arginine
Fumarate can enter the dicarboxylate cycle and become aspartate which is necessary for the previous step in which citrulline becomes arginosuccinate using the enzyme arginosuccinate synthase

M1 Biochemistry (17 decks)

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