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Medical Biochemistry -1b > 30-AMINO ACID METABOLISM LECTURE 1-3 - Dr. Venk. > Flashcards

30-AMINO ACID METABOLISM LECTURE 1-3 - Dr. Venk. Flashcards

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USMLE® Step 1 flashcards
1
Q

What are ketogenic and glucogenic amino acids?

A

Ketogenic amino acids produce acetyl CoA and acetoacetyl CoA (not substrates for gluconeogenesis) and glucogenic amino acids produce OAA, alpha-ketoglutarate, fumarate, succinyl CoA, pyruvate and 3-phosphoglycerate (substrates for gluconeogenesis).

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2
Q

What are essential and nonessential amino acids? Name the essential amino acids.

A

Essential amino acids are amino acids that cannot be synthesized by the human body and must be supplied by diet. Nonessential amino acids can be synthesized by the body and, so, are not required in the diet.

Essential amino acids are PVT TIM HALL.

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3
Q

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

A

The mandatory keto acid is alpha-ketoglutarate and an amino acid involved in the transamination reaction is glutamate.

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4
Q

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

A

Pyridoxal phosphate is the coenzyme involved in the transamination reaction.

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5
Q

Describe the role of glutamine with reference to nitrogen catabolism.

A

Glutamine is used as a carrier of NH4+ in nitrogen catabolism.

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6
Q

What are the substrates and products of glutaminase?

A

Glutamine (substrates) —> glutamate + NH3 (products)

via glutaminase in the liver

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7
Q

What are the substrates and products of carbamoyl phosphate synthase?

A

NH4+ + HCO3- —-> carbamoyl phosphate via carbamoyl phosphate synthase I.

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8
Q

Name the two cellular compartments where the urea cycle operates.

A

The urea cycle operates within the mitochondrial matrix and the cytosol.

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9
Q

Name the allosteric activator of carbamoyl phosphate synthase I.

A

The allosteric activator of CPS-I is N-acetylglutamate.

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10
Q

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

A
  • carbamoyl glutamate (carbamoyl phosphate synthease or N-acetylgulatamate synthase deficiency)
  • benzoate or phenyoacetate ( ornithinine transcarbomylase (OTC) deficiency ) **

feels like this is more correct

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11
Q

In an exercising muscle, name the cycle that utilizes an amino acid and converts it to glucose. What are the differences between the glucose-alanine cycle and the Cori cycle?

A

The glucose-alanine cycle.

Differences between glucose-alanine cycle and Cori cycle are:

  1. glucose-alanine cycle converts alanine to pyruvate in the liver
  2. the Cori cycle converts lactate to pyruvate in the liver
  3. the Cori cycle starts in the muscle with the creation of lactate then proceeds to the liver.
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12
Q

Name two neurotransmitters that are derived from tyrosine.

A

Two neurotransmitters derived from tyrosine are epinephrine and dopamine.

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13
Q

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

A

Three types of reactions involved in producing a neurotransmitter from an amino acid precursor are decarboxylation, hydroxylation, and SAM [S-adenosylmethionine]-dependant methylation.

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14
Q

Name three catecholamines.

A

Three catecholamines are epinephrine, dopamine, and norepinephrine.

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15
Q

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

A

The rate-limiting step in the biosynthesis of catecholamines is the tyrosine hydroxylase catalyzed reaction.

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16
Q

Name the cofactor that is required for tyrosine hydroxylase.

A

The cofactor required for the tyrosine hydroxylase reaction is THB, or tetrahydrobiopterin.

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17
Q

Catecholamine release is stimulated by the neurotransmitter ____________.

A

acetylcholine

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18
Q

Name two enzymes that are involved in catecholamine catabolism.

A

Catecholamine-O-Methyl Transferase (COMT) and Monoamine Oxidase (MAO).

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19
Q

Name a few functions of catecholamines.

A

Catecholamines are responsible for:

1) increased cardiac output, decreased peripheral vascular resistance to flow,
2) increased glycogen degradation, increased release of glucose to blood, increased triglyceride hydrolysis, and
3) increased fatty acid release from adipose tissue; in other words, they prepare the body for the fight o flight response.

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20
Q

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

A

Parkinson’s disease results from a loss in the substantia nigra, which is the area of the brain in which dopamine is produced. The lack of dopamine is supplemented with L-DOPA, which is the precursor for dopamine.

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21
Q

Name two neurotransmitter compounds that are derived from tryptophan.

A

melatonin and serotonin

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22
Q

What is the hormone that is involved in circadian rhythms?

A

melatonin

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23
Q

What is the effect of Prozac?

A

Prozac is a selective serotonin reuptake inhibitor. It inhibits the reuptake and degradation of serotonin in the post-synaptic cleft, making serotonin more available for binding.

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24
Q

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

A

For the treatment of jet lag, the pathway that would be targeted for drug therapy would be the synthesis of melatonin since melatonin is responsible for controlling diurnal (daily) cycles.

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25
Q

Name the enzyme that catalyzes the formation of histamine.

A

histidine decarboxylase

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26
Q

Name three functions of histamines.

A

Histamines are responsible for the

1) inflammatory/allergic response,
2) vasodilation, and
3) constriction of bronchioles in lungs and excretion of HCl in the stomach.

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27
Q

What are the substrates and products of glutamate decarboxylase?

A

Glutamate (substrate) —-> GABA (inhibitory neurotransmitter) (product)

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28
Q

In general, decarboxylases require the coenzyme ________________.

A

pyridoxal phosphate (B6 derivative)

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29
Q

L-DOPA is used for _________ disease treatment.

A

Parkinson’s

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30
Q

Name a synthetic compound that inhibits the serotonin reuptake.

A

Prozac, as well as others in the class of compounds generally known as SSRIs, inhibit the reuptake of serotonin.

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31
Q

Describe pheochromocytoma.

A

Pheochromocytomas are chromaffin tissue tumors which increase release of catecholamines, leading to increased blood pressure.

Side Note: cromaffin tissue is a tissue composed largely of chromaffin cells, well supplied with nerves and vessels; it occurs in the adrenal medulla and also forms the paraganglia of the body

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32
Q

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

A

Decreased levels of GABA and GABAnergic neurons are responsible for the symptoms of Huntington’s disease.

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33
Q

Melanins are synthesized in _________.

A

melanocytes

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34
Q

Tyrosinase deficiency causes ________.

A

albinism

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35
Q

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

A

In order to maintain the reducing environment within the cell, Glutathione (GSH) is the compound invoked.

36
Q

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

A

S-adenosylmethionine (SAM)

37
Q

Name two functions of glutathione.

A

Glutathione:

1) maintains protein sulfhydryl groups in the reduced state, which maintains the reducing environment within the cell
3) serves to detoxify xenobiotics by conjugation.

38
Q

Nitric oxide is derived from the amino acid _______.

A

arginine

39
Q

Name the substrate and products of acetylcholinesterase.

A

ACh (substrate) —-> choline + acetate (products)

40
Q

Explain the action of DIPF on acetylcholinesterase.

A

DIPF, a component of nerve gases, covalently modifies acetylcholinesterase by fluorination which knocks out the enzyme activity.

[In more detail: the serine residue at the active site on AChE reacts with the phosphate group on DIPF, and with the elimination of fluorine, forms a covalent bond that knocks out enzyme activity]

41
Q

Name some xenobiotics that inhibit acetylcholinesterase.

A

Physostigmine and neostigmine are two xenobiotics that inhibit acetylcholinesterase.

42
Q

Name the channel that is opened up by acetylcholine.

A

Na+/K+ channel in post-synaptic vesicles after a nerve stimulus.

43
Q

Discuss the mechanism of action of nerve gas.

A

Nerve gases covalently modify acetylcholinesterase, knocking out the enzyme activity. Death results due to respiratory paralysis.

44
Q

Name three excitatory and three inhibitory neurotransmitters.

A

Three excitatory neurotransmitters are acetylcholine, dopamine, aspartate, epinephrine, histamine, and 5-hydroxytryptamine.

Three inhibitory neurotransmitters are glycine, taurine, and 4-aminobutyrate.

45
Q

Name the three stages of nerve transmission.

A

The three stages of nerve transmission are 1) resting, 2) excitation, and 3) termination.

46
Q

What is the action of GABA?

A

GABA increases the permeability of post-synaptic membranes to chloride ion, increasing hyperpolarization and inhibiting action potential.

47
Q

What is the function of phenobarbital?

A

Phenobarbital binds to GABA receptors, inhibiting action potentials.

48
Q

Name the catabolic products of GABA.

A

The catabolic products of GABA are succinate semialdehyde, and subsequently, succinate.

49
Q

What is an ion-gated channel?

A

An ion-gated channel is a channel that is regulated by the flux of ions through the channel.

50
Q

Name two ion channels.

A

Na+/K+ channel and Ca2+ channel

51
Q

Diisopropylphosphofluoridate (DIPF) inhibits the enzyme ____________.

A

acetylcholinesterase

52
Q

Name two inhibitors of the acetylcholine receptor.

A

Two inhibitors of the acetylcholine receptor are tubocurarine, cobratoxin and alpha-bungarotoxin

53
Q

What are glial cells? Descrbe some of the biochemical functions of microglia, astrocytes and oligodendrocytes.

A

Glial cells are supporting neuronal cells that maintain the normal physiology of the nervous system.

Microglia - release inflammatory substances in response to injury that can damage neurons. Their purpose is to fight infections.

Astroycytes - An integral part of synapses, they regulate molecules necessary for neuron communication.

Oligodendrocytes - provide fatty myelin sheaths that insulate the axon.

54
Q

Acetylcholine is not metabolized by reuptake process. Explain which cells would catabolize the actylcholine after the action potential.

A

The acetylcholinesterase on the postsynaptic cell would catabolize the acetylcholine after the action cell.

55
Q

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

A

…

56
Q

What are the normal blood creatine values

A

< 1.5 mg/Dl

57
Q

Describe the metabolism of glucogenic and ketogenic amino acids in relation to TCA cycle.

A

Glucogenic amino acids are metabolized to TCA cycle intermediates. Ketogenic amino acids are metabolized to non-TCA cycle producs.

58
Q

Describe lactate dehydrogenase catalyzed reaction.

A

In the lactate deyhydrogenase reaction, Pyruvate is converted to lactate via the Muscle (M) isoform of lactate dehyrogenase with the consumption of NADH.

In the liver, lactate is being converted back to Pyruvate via the Liver (L) isoform of lactate hydrogenase, with the aid of NAD+.

59
Q

When lactate accumulates in the lbood it is a problem. WHy?

A

Results in low pH, and therefore acidosis

60
Q

Describe the actecholamine synthesis pathway

A

Choline and Acetyl CoA —-> Acetylcholine + CoA via choline acetyltransferase.

i.e. the acetyl part of Acetyl CoA is transferred to Choline to make acetylcholine.

61
Q

Explain why citain B6 deficiency can cause brian related problems

A

Vitamin B6 is necessary for decraboxylase and a difeciiency causes brain related problems.?

62
Q

Describe the biosynthesis of serotonin and melatonin

A

Serotonin is synthesized from the amino acid tryptophan.

First, Tryptophan + Oxygen –> 5 hydroxytryptophan (via tryptophan dehydroxylase and cofactor THB)

Then 5-hydroxytryptophan –> Serotonin (via Decarboxylase)

To synthesize Melatonin,
Serotonin –> N-acetyl serotonin (via N-acetyl transferase (NAT))

N-acetyl serotonin –> melatonin (via metyltransferase)

The rate limiting enzyme is tryptophan hydroxylasse, which requires O2 and cofactor tetrahydropbiopterin (THB)

63
Q

Describe the biosynthesis of histamine and its function

A

Histine is converted to Histamine (via histidine decarboxylase and coenzyme pyridoxal phosphate).

The function of histidine is

1) mediate allergic and inflammatory reactions (mast cells)
2) power vasodilator
3) constriction of bronchioles in lungs and stimulates secretion of HCl in stomach.

64
Q

Describe the biosynthesis of creatine phosphate and its degradation.

A

Creatine phosphate is created from arginine and glycinethat undergoes a transamidase reaction, metylation via SAM, and finally creatine kinase enzyme w/ ATP to form creatine phosphate.

Degradation of phosphocreatine uses non-enzymatic conversion to creatintine.

65
Q

Which vitamin derivative is required as a cofactor for many of the decarboxylases

A

B6

66
Q

Describe three nitric oxide synthases and the respective functions of the nitric oxides

A

1) endothelium derived: activates cytosolic guanylate cyclase –> increases cGMP –> leads to phosphorylation of smooth muscle and relaxation
2. Brain derived: results in cGMP synthesis
3) Macrophage derived: toxic to bacteria.

67
Q

Describe the biochemical basis for Parkinson’s

A

lack of dopamine

68
Q

Describe the biochemical basis for depression

A

serotonin reuptake in the presynpatic cell

69
Q

Describe the biochemical basis for pheochromocytomas

A

lots of catecholamines => hypertension

70
Q

Describe the biochemical basis for Hunginton’s

A

trinucleotide (CAG) repeat expansion

71
Q

Describe the biochemical basis for epilepsy

A

…

72
Q

Describe the biochemical basis for albinism

A

tyrosinase deficiency -> defective melanin production

73
Q

Describe the biochemical basis for allergy

A

A histamine reaction from mast cells

74
Q

Describe the biochemical basis for sleep derailment

A

…

75
Q

Describe the biochemical basis for Alzheimers

A

acetylcholine deficiency

76
Q

Describe in detail the glucose/alanine and Cori cycle

A

…

77
Q

What are the normal BUN values

A

~10-20 mg/dL

78
Q

Name three amino acid specific transminases

A

…

79
Q

Describe the dicarboxylate cycle

A

…

80
Q

Describe the connection between dicarboxylate and the urea cycle

A

…?

81
Q

Describe the lactate dehydrogenase reaction in reference to Coris’s cycle

A

Lactate dehydrogenase is the primary reaction in Cori’s cycle, which converts lactate to pyruvate (L) or pyruvate to lactate (M)

82
Q

What is the compound produced upon degradation of a ketogenic amino acid?

A

acetoacetate or acetyl CoA

83
Q

What is an allosteric activator of caramoyl phosphate synthase I (CPS-1)?

A

N-acetylglutamate

84
Q

For urea cycle enzyme deficiency, excess ammonium production can be avoided by administering what?

A

phenyl acetate

85
Q

What are three inhibitors of acetylcholine receptor?

A

Tubocurarine, alpha-bungarotoxin and cobra toxin

Medical Biochemistry -1b (6 decks)

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