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MGM (D) > Lecture 47 > Flashcards

Lecture 47 Flashcards

1
Q

What are three types of amino acids that can be catabolized for use of their carbon skeletons?

A

Amino acids can be classified as glucogenic, ketogenic, or both, based on which of the 7 intermediates are produced during their catabolism

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2
Q

What are the nonessential glucogenic amino acids?

A

Alanine, Arginine, Asparagine, Aspartate, Cysteine, Glutamate, Glutamine, Glycine, Proline, & Serine

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3
Q

What are nonessential ketogenic amino acids?

A

None

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4
Q

What are nonessential ketogenic & glucogenic amino acids?

A

Tyrosine

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5
Q

What are essential glucogenic amino acids?

A

Histidine, Methionine, Threonine, & Valine

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6
Q

What are essential ketogenic amino acids?

A

Leucine & Lysine

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7
Q

What are essential ketogenic & glucogenic amino acids?

A

Isoleucine, Phenyl-alanine, & tryptophan

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8
Q

Can some amino acids be conditionally essential?

A

Yes. For example, supplementation with glutamine & arginine has been shown to improve outcomes in patients with trauma, postoperative infections, & immunosuppression

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9
Q

How are asparagine and aspartate metabolized to form oxaloacetate?

A

1) Asparagine –> Aspartate (uses Asparaginase)

2) Aspartate + alpha-ketoglutarate –> Glutamate + Oxaloacetate (uses Aspartate aminotransferase)

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10
Q

What is lacking in leukemia cells and how can leukemic patients be treated?

A

1) Some leukemia cells are unable to synthesize sufficient asparagine to support their growth
2) Asparaginase can be administered systemically to treat leukemic patients

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11
Q

What are 7 intermediate products that are formed as byproducts of catabolism of carbon skeletons of amino acids?

A

1) Pyruvate
2) Acetyl CoA
3) Acetoacetate
4) Oxaloacetate
5) alpha-ketoglutarate
6) Succinyl CoA
7) Fumarate

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12
Q

What is the process by which histidine is degraded to form alpha-ketoglutarate via glutamate?

A

1) Histidine –> Urocanic acid (uses histidase)
2) Urocanic acid –> N-Formimino-glutamate (FlGlu)
3) N-Formimino-glutamate (FlGlue) + Tetrahydro-folate –> Glutamate + N5-Formimino-tetrahydrofolate
4) Glutamate –> alpha-ketoglutarate

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13
Q

How is alanine transaminated to form pyruvate?

A

L-Alanine + alpha-ketoglutarate –> Pyruvate + Glutamate (uses Alanine aminotransferase [Pyridoxal phosphate (PLP)])

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14
Q

What is Pyridoxal phosphate (PLP)?

A

1) Pyridoxal-phosphate (PLP) is a prosthetic group of certain enzymes
2) PLP is also the active form of vitamin B6
3) This co-factor acts as an electron sink to stabilize carbanionic intermediates in both substitution and elimination reactions involving aminated compounds
4) It is a co-factor of Alanine aminotransferase

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15
Q

How is phenylalanine degraded to form tyrosine, and then fumarate & acetoacetate

A

1) L-Phenylalanine + Tetrahydro-biopterin + O2 –> L-Tyrosine + Dihydro-biopterin + H2O (uses Phenylalanine hydroxylase)
2) L-tyrosine –> Fumarate
3) L-tyrosine –> Acetoacetate

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16
Q

How can Methionine be degraded or reformed?

A

1) Using methyltransferases, L-methionine can be demethylated to form L-homocysteine and release adenosine in the process
2) L-homocysteine can then be further degraded to form L-cysteine
3) L-homocysteine can also use methionine synthase to reform L-methionine (methylation)

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17
Q

What cofactors are required to form methionine and cysteine?

A

1) Conversion to methionine requires folate & vitamin B12-derived coenzymes (this is a remethylation process)
2) Formation of cysteine requires vitamin B6 (pyridoxine), and is a transsulfuration process - the sulfur of methionine becomes the sulfur of cysteine

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18
Q

Describe the degradation of leucine

A

1) Leucine is transaminated to form alpha-ketoiso-caproic acid
2) Alpha-ketoiso-caproic acid undergoes oxidative decarboxylation to form Isovaleryl CoA
3) Isovaleryl CoA undergoes FAD-linked Dehydrogenation to form Beta-methyl-crotonyl CoA
4) Beta-methyl-crotonyl CoA eventually forms HMG CoA and then acetoacetate + acetyl CoA

19
Q

Describe the degradation of valine

A

1) Valine is transaminated to form alpha-ketoiso-valeric acid
2) alpha-ketoiso-valeric acid undergoes Oxidative decarboxylation to form isobutyryl CoA
3) Isobutyryl CoA undergoes FAD-linked dehydrogenation to form propionyl CoA
4) Propionyl CoA eventually forms Succinyl CoA

20
Q

Describe the degradation of isoleucine

A

1) Isoleucine is transaminated to form alpha-keto-beta-methyl-valeric acid
2) alpha-keto-beta-methyl-valeric acid undergoes oxidative decarboxylation to form alpha-methyl-butyryl CoA
3) alpha-methyl-butyryl CoA undergoes FAD-linked dehydrogenation to form propionyl CoA
4) Propionyl CoA eventually forms succinyl CoA

21
Q

What becomes deficient in maple syrup urine disease?

A

Oxidative decarboxylation of branched-chain amino acids is deficient in maple syrup urine disease

22
Q

How are alanine, aspartate, & glutamate formed with their corresponding alpha-keto acids?

A

1) Pyruvate + Amino acid –> alpha-keto acid + alanine
2) Oxaloacetate + amino acid –> Aspartate + alpha-keto acid
3) alpha-ketoglutarate + amino acid –> Glutamate + alpha-keto acid
4) Each of the above reactions uses an aminotransferase with PLP

23
Q

Describe the formation of dopamine from tyrosine

A

1) Tyrosine + Tetrahydro-biopterin + O2 –> 3,4-Dihydroxy-phenylalanine (DOPA) + Dihydro-biopterin + H2O (uses Tyrosine hydroxylase - rate limiting step)
2) 3,4-Dihydroxy-phenylalanine (DOPA) –> Dopamine (uses aromatic amino acid decarboxylase; releases CO2)

24
Q

Describe the formation of Norepinephrine from Dopmaine

A

Dopamine + Ascorbate + O2 –> Norepinephrine + Dehydro-ascorbate + H2O (Uses Dopamine beta-hydroxylase with a Cu2+ as a cofactor)

25
Q

Describe the formation of epinephrine from norepinephrine

A

Norepinephrine + S-Adenosyl-methionine –> S-Adenosyl-homocysteine + Epinephrine (uses phenylethanolamine-N-methyl-transferase)

26
Q

What does cocaine do?

A

Cocaine inhibits dopamine and norepinephrine reuptake in the brain

27
Q

What is Parkinson disease?

A

1) Common neurodegenerative movement disorder affecting 1 million people in the US
2) Symptoms: paucity of spontaneous movement, tremor at rest, muscle rigidity, shuffling gait, mask-like facial expression, autonomic disturbances, depression, & cognitive impairment
3) Results from degeneration of dopamine neurons in the substantia nigra pars compacta
4) Oral administration of L-DOPA was found beneficial but effects diminish after 5 years

28
Q

Why is L-DOPA given to patients with parkinsons disease rather than direct dopamine?

A

L-DOPA can cross the blood-brain barrier, while dopamine cannot

29
Q

Can parkinsons disease be inherited?

A

Yes. There are five nuclear genes that are known to carry mutations that cause rare inherited forms (<10%) of Parkinson disease

30
Q

How are epinephrine and norepinephrine metabolized?

A

Metabolism of the catecholamines (epinephrine & norepinephrine) uses catechol-O-methyl transferase (COMT) and monoamine oxidase (MAO) to form Vanillylmandelic acid (VMA)

31
Q

How is dopamine metabolized?

A

Metabolism of the catecholamine (dopamine) uses catechol-O-methyl transferase (COMT) and monoamine oxidase (MAO) to form Homovanillic acid (VMA)

32
Q

What were antidepressants first made from?

A

Monoamine oxidase (MAO) inhibitors?

33
Q

How is serotonin produced?

A

1) Tryptophan + Tetrahydro-biopterin –> 5-Hydroxy-tryptophan + Dihydro-biopterin + H2O (uses hydroxylase)
2) 5-hydroxy-tryptophan –> Serotonin + CO2 (uses Aromatic amino acid decarboxylase with PLP)

34
Q

What is formed when serotonin is degraded by monoamine oxidase (MAO)?

A

Hydroxyindole acetic acid

35
Q

What does the antidepressant Fluoxetine (Prozac) do?

A

It inhibits serotonin reuptake

36
Q

How is GABA (gamma-aminobutyrate) formed?

A

Glutamate –> GABA + CO2 (uses glutamate decarboxylase with PLP)

37
Q

How does glutamate work?

A

1) Glutamate acts via ionotropic (Na+, Ca2+) and metabotropic (GPCR) recepors
2) Glutamate is the major excitatory neurotransmitter in human brain
3) Chronic release can lead to excitotoxicity

38
Q

How does GABA work?

A

1) GABA acts via ionotropic (Cl-) and metabotropic (GPCR) receptors
2) It is the major inhibitory neurotransmitter in the brain

39
Q

How is histamine formed?

A

Histidine –> Histamine + CO2 (uses histidine decarboxylase with PLP)

40
Q

What does histamine do?

A

Histamine is a chemical messenger that mediates allergic and inflammatory reactions and gastric acid secretion

41
Q

How is melatonin formed?

A

1) Serotonin + AcCoa –> N-acetylserotonin + CoASH (uses AANAT)
2) N-acetylserotonin –> Melatonin (uses HIOMT)

42
Q

What accounts for melatonin formation?

A

While levels of HIOMT activity remain fairly constant, the daily rhythm in melatonin synthesis is generated by a concurrent rhythm in AANAT activity

43
Q

Describe the synthesis of creatine

A

1) Arginine + Glycine –> Guanidinoacetate + Ornithine (uses Amidino-transferase)
2) Guanidinoacetate + S-Adenosylmethionine –> S-Adenosylhomocysteine + Creatine (uses methyltransferase)

44
Q

What can creatine be used to form?

A

1) Creatine + ATP –> Creatine phosphate + ADP + H+ (uses creatine kinase)
2) Creatine –> Creatinine + H2O
3) Creatinine phosphate –> Creatinine + Pi

MGM (D) (71 decks)

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