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Gastroenterology4 > Protein Metabolism > Flashcards

Protein Metabolism Flashcards

1
Q

What are the three types of amino acids?

A

Essential, conditionally essential, and nonessential amino acids

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2
Q

How can certain nonessential amino acids become essential?

A

Under certain conditions and states

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3
Q

What is the daily protein requirement for high-quality protein?

A

0.8 g per kg ideal body weight

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4
Q

What is the term for the constant breakdown and synthesis of body proteins?

A

Turnover

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5
Q

What is the range of half-lives for proteins?

A

From 11 minutes to life-long

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6
Q

How are extracellular and membrane proteins catabolized?

A

Via endocytosis and fusion with lysosomes

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7
Q

What system degrades intracellular proteins?

A

Ubiquitin Proteasome System (UPS)

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8
Q

What is the primary waste product from excess nitrogen?

A

Urea

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9
Q

What are the daily unavoidable nitrogen losses?

A

Must be replaced by synthetic reactions using dietary amino acids

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10
Q

What is the first form of Protein-Energy Malnutrition (PEM)?

A

Kwashiorkor

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11
Q

What characterizes Kwashiorkor?

A

Protein deficiency with sufficient carbohydrates, edema

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12
Q

What is the second form of Protein-Energy Malnutrition (PEM)?

A

Marasmus

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13
Q

What characterizes Marasmus?

A

Deficiency in both calorie and protein, no edema

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14
Q

What is the mnemonic for essential amino acids?

A

PVT TIM HALL

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15
Q

What are the essential amino acids represented by the mnemonic?

A
  • Phe
  • Val
  • Thr
  • Trp
  • Ile
  • Met
  • His
  • Arg
  • Leu
  • Lys
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16
Q

What is the role of gastric parietal cells?

A

Secrete HCl to partially denature proteins

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17
Q

What activates pepsin in the stomach?

A

The acidic environment through self-cleavage

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18
Q

What activates trypsinogen in the small intestine?

A

Enteropeptidase

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19
Q

What is the primary transport mechanism for free amino acids into cells?

A

Na+-dependent transport

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20
Q

What condition is characterized by defective transport of large neutral amino acids?

A

Hartnup disease

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21
Q

What condition is characterized by defective transport of basic amino acids?

A

Cystinuria

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22
Q

What is the function of ubiquitin in protein degradation?

A

Targets proteins for degradation by the proteasome

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23
Q

What are the FDA-approved proteasome inhibitors for treating multiple myeloma?

A
  • Velcade (Bortezomib)
  • Kyprolis (Carfilzomib)
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24
Q

What is the acidic environment in lysosomes primarily maintained by?

A

Vacuolar H+ ATPase

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25
Q

What are the two types of autophagy?

A
  • Micro-autophagy
  • Macro-autophagy
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26
Q

What is the purpose of amino acid catabolism?

A
  • Provide materials/presursors for synthesis
  • Provide intermediates for TCA cycle
  • Provide intermediates for glucose or lipid biosynthesis
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27
Q

What are glucogenic amino acids?

A

Amino acids that produce pyruvate or TCA intermediates

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28
Q

What are ketogenic amino acids?

A

Amino acids that produce ketone bodies

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29
Q

What are the main enzymatic reactions involved in amino acid catabolism?

A
  • Aminotransferases
  • Glutamate Dehydrogenase
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30
Q

What is the role of glutamine in the body?

A

Non-toxic plasma transporter for ammonium to the liver

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31
Q

What amino acids are related to α-ketoglutarate?

A
  • Glutamine
  • Glutamate
  • Proline
  • Arginine
  • Histidine
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32
Q

What amino acids are related to oxaloacetate (OAA)?

A
  • Aspartate
  • Asparagine
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33
Q

What is FA oxidation?

A

Fatty acid oxidation process that breaks down fatty acids to generate energy

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34
Q

What does TCA cycle stand for?

A

Tricarboxylic Acid Cycle

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35
Q

Which amino acid is a non-toxic plasma transporter for ammonium to the liver?

A

Glutamine

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36
Q

Name two amino acids related to TCA cycle intermediates OAA.

A
  • Aspartate
  • Asparagine
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37
Q

List three amino acids related to TCA cycle intermediates fumarate.

A
  • Phenylalanine
  • Tyrosine
  • Glutamate
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38
Q

What is the Krebs bi-cycle?

A

The common steps between the TCA cycle and urea cycle

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39
Q

Identify two amino acids that are related to the TCA cycle intermediate Succinyl-CoA.

A
  • Methionine
  • Threonine
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40
Q

Which important vitamin is involved in the synthesis of Methionine?

A

B12

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41
Q

Fill in the blank: The five cofactors involved in branched-chain α-keto acid dehydrogenase are TPP, riboflavin, lipoic acid, pantothenic acid, and _______.

A

niacin

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42
Q

What is the main substrate of branched-chain α-keto acid dehydrogenase?

A

Branched-chain α-keto acids

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43
Q

What is Maple Syrup Urine Disease (MSUD)?

A

A deficiency of the branched-chain α-keto acid dehydrogenase leading to abnormal metabolism of leucine, isoleucine, and valine

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44
Q

What is a treatment for MSUD?

A

Strict dietary control of BCAA and possible supplementation with thiamine

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45
Q

Which amino acids are exclusively ketogenic?

A
  • Leucine
  • Lysine
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46
Q

What condition is characterized by defective transport of large neutral amino acids like tryptophan?

A

Hartnup disease

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47
Q

What is Phenylketonuria (PKU)?

A

A genetic disorder caused by a deficiency in the enzyme that metabolizes phenylalanine

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48
Q

What unusual metabolites appear in the blood and urine of PKU patients?

A
  • Phenylpyruvate
  • Phenylacetate
  • Phenyl lactate
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49
Q

What is the musty urine odor in PKU patients due to?

A

Unusual metabolites of phenylalanine

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50
Q

What is the incidence of classical PKU in newborns?

A

About 1 in 15,000 newborns

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51
Q

What dietary treatment is recommended for pregnant women with PKU?

A

Maintain low plasma levels of phenylalanine during gestation

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52
Q

What causes urine to darken in Alcaptonuria?

A

Oxidation and polymerization of homogentisate

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53
Q

Name two symptoms of Alcaptonuria.

A
  • Homogentisic aciduria
  • Arthritis
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54
Q

What is the clinical relevance of amino acid metabolism?

A

Understanding nitrogen balance, glucogenic and ketogenic amino acids, and related diseases

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55
Q

What is the treatment for cystinuria?

A

Dietary restriction of cysteine and methionine, increase fluid intake

56
Q

What is the condition characterized by excessive phenylalanine levels in infants?

A

Phenylketonuria (PKU)

57
Q

What is the main characteristic of lysosomal storage disorders?

A

Defects in lysosomal enzyme targeting or function

58
Q

What is the purpose of the Urea Cycle?

A

To dispose of nitrogen and excrete ammonia.

59
Q

Which substrates are involved in the Urea Cycle?

A
  • NH4+
  • HCO3-
  • Ornithine
  • Aspartate
60
Q

What are the main reactions of the Urea Cycle?

A

Involves the conversion of ammonium to urea in the liver through specific enzymatic reactions.

61
Q

What is the rate-limiting enzyme of the Urea Cycle?

A

Carbamoyl Phosphate Synthetase I (CPS-I)

62
Q

How is the Urea Cycle regulated?

A
  • Allosteric effectors
  • Substrate availability
  • Enzyme levels
63
Q

What are the causes of hyperammonemia?

A
  • Excess protein intake
  • Fasting
  • Trauma
  • Liver disease or toxins
  • Genetic defects in Urea Cycle enzymes
  • Intestinal bacteria
64
Q

True or False: High levels of ammonium are toxic to the CNS.

A

True

65
Q

What role does glutamate play in amino acid metabolism?

A

It is formed from the transfer of amino groups and can release ammonia.

66
Q

Fill in the blank: The Urea Cycle occurs primarily in the ______.

A

Liver

67
Q

What is the major nitrogenous excretory product of amino acid degradation?

A

Urea

68
Q

What is the significance of the Krebs bi-cycle in relation to the Urea Cycle?

A

It recycles fumarate back to aspartate, replenishing TCA cycle intermediates.

69
Q

What is the effect of a high protein diet on the Urea Cycle?

A

It induces the synthesis of urea cycle enzymes.

70
Q

How does the body transport ammonium to the liver?

A

Through glutamine and alanine as nitrogen carriers.

71
Q

What happens to urea excretion during fasting?

A

It is high during the first few days due to muscle proteolysis.

72
Q

What is the role of arginine in the Urea Cycle?

A

It stimulates the synthesis of N-Acetyl-Glutamate, activating CPS-I.

73
Q

What are the three main enzymatic reactions converting NH4+ to organic forms?

A
  • Glutamate Dehydrogenase (GDH)
  • Glutamine Synthetase
  • Carbamoyl phosphate synthetase I (CPS-I)
74
Q

What are the symptoms of hyperammonemia?

A
  • Tremors
  • Slurred speech
  • Blurry vision
  • Somnolence
  • Vomiting
  • Coma
  • Death
75
Q

What is the main function of aminotransferases?

A

To transfer amino groups to α-ketoglutarate, forming glutamate.

76
Q

What is the clinical significance of Blood Urea Nitrogen (BUN)?

A

High in kidney disease but generally low in liver failure.

77
Q

What happens to glutamine levels during acquired hyperammonemia?

A

They are generally high in the blood due to urea cycle backup.

78
Q

What is the first step in the Urea Cycle?

A

Formation of Carbamoyl Phosphate by CPS-I.

79
Q

What is the role of Nitric Oxide Synthase (NOS) in relation to arginine?

A

It uses arginine to synthesize Nitric Oxide (NO).

80
Q

What is a common defect in congenital hyperammonemia?

A

Defects in Carbamoyl Phosphate Synthetase I (CPS I) or Ornithine TransCarbamoylase (OTC).

81
Q

What happens to muscle proteolysis as the brain adapts to ketone bodies during fasting?

A

The rate of muscle proteolysis and gluconeogenesis from muscle amino acids drops.

82
Q

What is the result of Ornithine TransCarbamoylase deficiency?

A

Excessive orotic acid in the urine

Orotic acid is an intermediate of the pyrimidine biosynthetic pathway.

83
Q

What symptoms do infants with urea cycle defects typically develop shortly after birth?

A

Lethargy, irritability, vomiting, and coma.

84
Q

What happens to ornithine levels in Argininosuccinate lyase deficiency?

A

Ornithine quickly becomes depleted.

85
Q

How can oral arginine help individuals with Argininosuccinate lyase deficiency?

A

It regenerates ornithine from arginine and stimulates the removal of carbamoyl phosphate.

86
Q

What does the buildup of carbamoyl phosphate lead to in Ornithine transcarbamoylase deficiency?

A

Increased synthesis of orotic acid.

87
Q

What is the main treatment strategy for hyperammonemia?

A

Low protein diet.

88
Q

What is one consequence of prolonged fasting in patients with hyperammonemia?

A

Increased muscle proteolysis.

89
Q

Which drugs are administered to dispose of excess glutamine and other amino acids in hyperammonemia?

A

Phenyl Butyrate, Phenyl Acetate, Benzoic Acid.

90
Q

What is the role of phenyl acetate in treating hyperammonemia?

A

It is activated to a CoA derivative, attaches to glutamine, and is excreted.

91
Q

What is the primary carrier of nitrogen atoms generated from amino acid catabolism?

A

Urea.

92
Q

Where does urea synthesis occur?

A

In the liver.

93
Q

Which amino acids carry nitrogen from peripheral tissues to the liver?

A

Alanine and Glutamine.

94
Q

What does the urea cycle incorporate to form urea?

A

One nitrogen from free ammonia and another from aspartate.

95
Q

What condition results from disorders of the urea cycle?

A

Hyperammonemia.

96
Q

What clinical symptoms were observed in the 5-month-old female infant with a urea cycle defect?

A

Periodic bouts of vomiting, failure to gain weight, irritability, and lethargy.

97
Q

What were the laboratory findings in the infant with urea cycle defect?

A

Increased plasma ammonia, increased glutamine, and low citrulline.

98
Q

Why was orotate noted to be excreted in the urine of the infant?

A

Due to the deficiency in Ornithine transcarbamoylase.

99
Q

What was the treatment provided to the infant upon hospital admission?

A

Intravenous phenylbutyrate and benzoate.

100
Q

Why was the infant put on a low protein diet?

A

To avoid increased ammonia levels from protein metabolism.

101
Q

What does the level of ornithine transcarbamoylase activity in the patient’s liver indicate?

A

About 10% of normal activity.

102
Q

True or False: The further down the urea cycle the defective enzyme is located, the more toxic effect is observed in the patient.

A

False.

103
Q

Fill in the blank: The urea cycle consists of ______ steps.

A

four

104
Q

Which enzyme is responsible for the conversion of glutamate and Acetyl CoA to N-Acetyl Glutamate?

A

N-Acetyl Glutamate Synthase.

105
Q

What is the pathogenesis of PKU

A

cells are not able to convert phenylalanine to tyrosine; Tyr becomes an essential amino acid for these pts.

106
Q

What vit. deficiency can result from insufficient or impaired transportation of tryptophan

A

niacin Vit. B3

107
Q

cytoplasmic membrane bound materials targeted for lysosomal degradation are transported into the lysosome via what cytosis mechanism

A

endocytosis

108
Q

large particles like bacteria cytosed into the lysosome via

A

phagocytosis

109
Q

pinocytosis into the lysosomal compartment is for what matter

A

fluid and small particles

110
Q

UPS functional inadequacy has been implicated in which 2 neurodegenerative diseases

A

Huntington’s & Alzheimer’s

111
Q

UPS functional inadequacy contributes to the oncogenesis of what protooncogenes

A

HMD2/MDM2 for p53

112
Q

Aminotransferases require what Vit.

A

Vit. B6/PLP

113
Q

ammonium is converted into what non-toxic metabolite

A

glutamine

114
Q

alpha-ketoglutarate, a TCA intermediate, can be used to synthesisze what amino acids

A

Glutamine
glutamate
proline
arginine
histidine

115
Q

what AAs rely on TCA intermediate oxaloacetate for synthesis

A

aspartate & Asparagine

116
Q

what AA rely on TCA intermediate fumarate for synthesis

A

phenylalanine & tyrosine

117
Q

what AAs rely on TCA intermediate succinyl-CoA for synthesis

A

methionine; threonine; isoleucine; valine

118
Q

what important vit. are invovled in the Succinyl-CoA AA pathway

A

B12 & folate for Met. synthesis
B6
Biotin
Thiamine

119
Q

what vit.s are required for activation of the branched-chain alpha-keto acid dehydrogenase

A

Thiamine (B1)
Riboflavin (B2)
Niacin (B3)
Pantothenic acid (B5)

120
Q

List the branched AAs

A

Leu; Ile; val

121
Q

what AAs are linked to intermediates of glycolysis

A

glycine; serine; cysteine; alanine

122
Q

what AAs form acetyl CoA & acetoacetate

A

F; Y; W; L; K; I

123
Q

Tyrosine is degraded into what TCA intermediate

A

fumarate

124
Q

what are clinical manifestations of alcaptonuria

A

spinal arthritis; dark ochronotic pigmentation of cartilage and collagenous tissue

125
Q

What affect does alcohol have on ammonium metabolism

A

decreases hepatic capacity to convert NH4 to urea

126
Q

What AA is the amino group donor for the urea cycle

A

aspartate

127
Q

what AA is the carbon donor for gluconeogenesis

A

most of them except lys & Leu

128
Q

does the rate of urea production increase or decrease during fasting state

A

it decreases

129
Q

what role do proteins play during the fasting state

A

their carbons are used for gluconeogenesis

130
Q

what enzyme converts gluamate to ammonium

A

glutamate dehydrogenase

131
Q

what AA carries ammonium from the muscle into the liver

A

alaline & glutamine

132
Q

what is the rate-limiting step for the Urea cycle

A

formation of Carbamoyl phosphate by CPS-I

133
Q

What Urea Cycle enzymes are invovled in the first 2 steps of Urea synthesis that take place in the mitochondria

A

CPS-I & OTCase

134
Q

describe the process by which the Urea Cycle is initiated

A

Arginine allosterically stimulates synthesis of NAG which allosterically activates CPSI

135
Q

Arginine is also used to produce what endothelial anti-inflammatory modulator

A

NO

Gastroenterology4 (8 decks)

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