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Val 307 > 4. Amino Acid and Protein Metabolism (Part I) > Flashcards

4. Amino Acid and Protein Metabolism (Part I) Flashcards

1
Q

Define the Estimated Average Requirement (EAR).

A

Defines the amount of a nutrient that supports a specific function in the body for HALF of the population

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2
Q

Define the Recommended Dietary Allowance (RDA).

A

The EAR + 2 standard deviations, which meets 97.5% of the population’s needs

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3
Q

What is the risk of deficiency at the RDA?

A

2.5%

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4
Q

What is the daily EAR for protein? How many grams is that for a 70 kg person?

A
  • 0.66 g/kg/d

- 46 g/d

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5
Q

What is the daily RDA for protein? How many grams is that for a 70 kg person?

A
  • 0.8 g/kg/d

- 56 g/d

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6
Q

What is the typical intake of protein in North America?

A
  • 80 to 100 g/d

- Substantially higher than the RDA

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7
Q

What should the EAR and RDA be, according to Dr. Wykes?

A
  • EAR: 0.9 g/kg/d

- RDA: 1.2-1.4 g/kg/d

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8
Q

What is the risk of deficiency at the EAR?

A

50%

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9
Q

How many amino acids are incorporated into proteins?

A

20 amino acids possess tRNAs, and are incorporated into proteins

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10
Q

Define indispensable amino acids.

A

Amino acids that are necessary to intake through the diet, as humans are incapable of producing these amino
acids de novo

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11
Q

Which amino acid was recently discovered to be indispensable in all ages?

A
  • Histidine

- Histidine requirement is difficult to measure, and was initially thought to be necessary solely in children

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12
Q

Define conditionally indispensable amino acids.

A

Amino acids that are required under certain metabolic conditions or developmental states, but are generally not required for healthy human

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13
Q

Which amino acid is responsible for carrying amino groups through the urea cycle? What is another one of its functions?

A
  • Arginine

- Precursor for powerful metabolic regulators (e.g. polyamines, creatine in muscle)

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14
Q

What occurs if an individual is deficient in arginine?

A
  • Build-up of amino groups, which are toxic to the brain

- Arginine is necessary to carry amino groups through the urea cycle

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15
Q

Why is arginine conditionally indispensable? Under what conditions is it required?

A
  • Babies require arginine
  • Individuals with a high turnover of protein (e.g. burns) require arginine
  • Normal healthy adults do NOT require arginine
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16
Q

Which amino acid requirements are considered together?

A
  • Tyrosine is synthesized from phenylalanine

- Cysteine is synthesized from methionine

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17
Q

What is tyrosine synthesized from?

A

Phenylalanine

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18
Q

What is cysteine synthesized from?

A

Methionine

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19
Q

What are the indispensable amino acids?

A
  • Valine
  • Phenylalanine
  • Histidine
  • Leucine
  • Methionine
  • Tryptophan
  • Isoleucine
  • Threonine
  • Lysine
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20
Q

What are the conditionally indispensable amino acids?

A
  • Tyrosine
  • Cysteine
  • Arginine
  • Glutamine
  • Glycine
  • Proline
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21
Q

What are the dispensable amino acids?

A
  • Alanine
  • Aspartate
  • Asparagine
  • Glutamate
  • Serine
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22
Q

How did the amino acid EARs between the FAO/WHO in 1985 differ from the DRI report in 2005? What was the exception?

A
  • The requirements for the amino acids doubled, and largely increased
  • Except for methionine and cysteine, which did not change
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23
Q

Why did methionine and cysteine requirements not change from the FAO report in 1985?

A
  • Because there was a transcription error in the FAO report

- The proposed RDA, and not the proposed EAR, was written

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24
Q

What specific principle does tracer dilution rely on?

A
  • We do NOT store amino acids or proteins
  • They are either used as building blocks, or catabolized
  • We maintain a constant pool of amino acids, unlike lipid or carbohydrate pool
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25
Q

What are the four assumptions of tracer dilutions?

A

1) System is at steady-state
2) Homogeneity of the pool
3) Massless tracer, which behaves like tracee
4) No tracer recycling

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26
Q

Why is the system at steady-state in a tracer dilution?

A

Constant flow of amino acids into the pool = the constant flow out

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27
Q

How is the amino acid pool assumed to be homogeneous in a tracer dilution? Is this a correct statement?

A
  • The concentration of an amino acid is assumed to be the same in plasma as in brain cells as in liver cells
  • Assumption that there is rapid mixing between sub-compartments
  • This is NOT true, but this approximation is necessary for the model
  • The concentration of a tracer is measured in a blood sample, and assumed that it represents the concentration in the rest of the body
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28
Q

Why is the tracer assumed to be massless in a tracer dilution?

A
  • The tracer administered is assumed to NOT be nutritionally significant
  • The tracer amino acid behaves metabolically similar to regular amino acids
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29
Q

Why is it assumed that there is no tracer recycling in a tracer dilution?

A

If there was recirculation of the tracer, there will be extra tracer coming in that is not accounted for, which influences the calculated flow number

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30
Q

What is the calculation for flow in a tracer dilution?

A

Flow = (Tracer infusion rate)/(Tracer concentration in pool)

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31
Q

Where are proteins stored?

A
  • Proteins are NOT stored, even not in muscle

- Muscle proteins are made to accomplish a function

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32
Q

What are the two routes of amino acid intake?

A
  • Diet intake

- Proteolysis

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33
Q

What are the two routes of amino acid expenditure?

A
  • Protein synthesis

- Amino acid oxidation

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34
Q

If the rate of tracer infusion is known, what may be determined?

A

The quantity of dilution may be measured with a plasma sample

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35
Q

What are isotopes?

A

Different forms of the same element, with nuclei that have the same number of protons but different numbers of neutrons

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36
Q

What element incorporated into water forms heavy water?

A

Deuterium (2H)

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37
Q

What isotopes are preferred to be used as tracers?

A

Stable isotopes that are NON-radioactive

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38
Q

How do you measure stable isotope tracers, and differentiate them?

A
  • Tracers isotopes are heavier, thus they may be uncovered by weight
  • Gas Chromatograph Mass Spectrometer
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39
Q

How does a GCMS function?

A

1) Temperature is increased to 300oC
2) Sample is injected, and heated to a gas
3) The molecules are placed in the middle of a magnet, and electrons are shot at them, producing ions in a specific way
4) Ions are sent through focusing lenses and a quadrupole mass analyzer, causing them to spiral down the rods at hit the detector at the end

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40
Q

How was essentiality determined historically?

A
  • They cannot be synthesized by the organism out of materials ordinarily available to the cells at a speed commensurate with the demands for normal growth
  • Determined with growth as a measure for accuracy
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41
Q

In a strictly metabolic sense (i.e. with the appropriate precursors), which amino acids CANNOT be synthesized by providing precursors?

A
  • Lysine
  • Threonine
  • Tryptophan
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42
Q

Why must amino groups be escorted in the body through transamination reactions?

A

Because free amino groups are toxic to the brain (ammonia)

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43
Q

What is a keto acid?

A

An amino acid without the amino group

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44
Q

Would the body be able to synthesize the branched-chain amino acids if we provided their keto acids? What conclusion does this bring about?

A
  • Yes
  • Thus, metabolically, they are not essential
  • But, nutritionally, they are essential, as we cannot normally supply the keto acid versions of these amino acids
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45
Q

What approach may be used in individuals with liver or kidney disease, who are sensitive to supplementary amino groups?

A
  • Providing branched-chain amino acids in the nutrition support regimen as KETO acids
  • Synthesis to amino acids gets rid of the body’s amino groups
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46
Q

What was the premise behind the Golden Egg Experiment?

A
  • Algae was grown in an atmosphere with 13CO2
  • Protein from the algae contained 13CO2, and was fed to the chicken
  • The chickens incorporated these amino acids into their own protein, including their egg protein
  • The eggs were then analyzed to measure which amino acids they contained
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47
Q

What results occurred in the Golden Egg Experiment for indispensable amino acids, such as phenylalanine?

A
  • Two fractions: M (protein breakdown) and M+9 (diet)
  • There were NO phenylalanine molecules that contained other types of labels
  • Thus, there was no resynthesis of phenylalanine in the body, which demonstrates that it is an essential amino acid
  • M decreased over days of feeding, while M+9 increased
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48
Q

How did the levels of phenylalanine differ between different tissues, 30 days after the Golden Egg Experiment? What does that suggest?

A
  • The liver had the highest, while muscle had the lowest
  • Indicates that protein synthesis is much faster in the liver than in muscle (slow protein-turning pool)
  • Other visceral organs have rapid metabolism and protein turnover (high incorporation of label)
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49
Q

What is the metabolic fuel for the gut?

A

Glutamate

50
Q

What is glutamine? How does it compare to glutamate?

A

Glutamine is a glutamate with an extra amino group

51
Q

What common function do glutamine and glutamate share?

A

Used in transporting amino groups from protein catabolism in peripheral tissues to the liver for urea synthesis

52
Q

What results occurred in the Golden Egg Experiment for dispensable amino acids, such as glutamine and glutamate?

A
  • Multiple fractions: M (protein breakdown) and M+1-9 (diet)
  • 70% of glutamate originated from protein breakdown (endogenous)
  • Multiple fractions demonstrated that the body assembled new glutamate in the body from labeled precursors that came from dietary amino acids
  • Carbon is exchanged between these amino acids and the precursors and intermediates of the Krebs cycle
53
Q

Why does the body use a substantial quantity of glutamate and glutamine?

A

Since they are amino acids that are used in the Cori Cycle to transport nitrogen from peripheral tissues to the liver

54
Q

What explains that limited quantities of dietary glutamate was synthesized into egg protein?

A

The gut uses oxidized glutamate as a metabolic fuel

55
Q

Define requirement.

A

The minimal intake level, representing a single point on a dose-response curve, which is sufficient to maintain a specific criterion of nutrition adequacy

56
Q

What are 7 ways to measure amino acid requirement?

A
  • Growth
  • Nitrogen balance
  • Plasma AA response
  • Direct AA oxidation
  • Indicator AA oxidation
  • 24h AA balance
  • Or measure of organ or system function
57
Q

What are general aspects to experimental approaches to measuring amino acid requirement?

A
  • All methods should give the same answer
  • Measures of individuals’ requirements
  • Subjects should be studied at above or equal to 6 test amino acid intake levels above and below requirement
  • Endpoint should show a clear
58
Q

If an individual consuming a low-amino acid switches to a high-amino acid diet, does the body need time to adapt to the change to increase catabolism of amino acids?

A

Certain individuals say yes, and others no

59
Q

If you are tracking the nitrogen part of an amino acid, how many hours/days does it take for the urea pool to be adapted for a person on a diet?

A
  • The amino acid pools are extremely small, while the urea cycle is extremely large and possesses slow protein turnover
  • It takes 7 to 10 days before the urea pool is adapted
60
Q

If you are tracking the oxidation of the amino acid be labelling the carbon, how many hours/days does it take to analyze the CO2 coming out in the breath?

A

Couple of hours to days

61
Q

In terms of nitrogen balance, how much dietary nitrogen is assumed to come from protein?

A

All the dietary nitrogen is assumed to come from protein

62
Q

What percentage nitrogen is protein by weight?

A

Protein is 16% nitrogen by weight

63
Q

What percentage of protein is absorbed, and what percentage is excreted in feces?

A
  • 95% of protein is absorbed and excreted in urine

- 5% is excreted in feces

64
Q

What is the formula for nitrogen balance?

A

Nitrogen Balance = Nitrogen Intake - Fecal Nitrogen - Urinary Nitrogen (- miscellaneous losses)

65
Q

How much nitrogen per kilogram is excreted in miscellaneous losses? What percentage does that represent in terms of protein requirement?

A
  • 5 mg of nitrogen per kilogram

- Represents between 2 and 5% of protein requirement

66
Q

What factors account for miscellaneous losses?

A
  • Sweat
  • Hair
  • Fingernails
67
Q

How does nitrogen balance differ for individuals in the tropics?

A

They excrete 10 mg in miscellaneous losses due to an increased amount of sweating

68
Q

What does “Apparent Nitrogen Balance” mean?

A

That miscellaneous losses are not considered

69
Q

What are the special products of amino acids? What are they generally assumed to be?

A
  • Ex: neurotransmitters

- Generally assumed to be 0, which is a bold assumption

70
Q

What does positive nitrogen balance indicate?

A
  • Protein synthesis > breakdown

- Results from a metabolic scenario of growth, recovery, increasing lean body mass, starting a protein-building regimen

71
Q

What is hypermetabolic positive nitrogen balance?

A
  • Synthesis > breakdown

- Child growing and catching up from malnutrition

72
Q

What is hypometabolic positive nitrogen balance?

A
  • Synthesis > breakdown

- Elderly person that is trying to recover from an illness

73
Q

Does increasing the intake above requirement from a well-nourished state drive positive nitrogen balance?

A
  • No, as it does not drive more protein synthesis, or less protein breakdown
  • Nitrogen balance should be maintained
74
Q

What is nitrogen balance in a state of malnutrition? How does this affect the quantity of amino acids excreted in urine?

A
  • Nitrogen balance is negative (synthesis < breakdown)
  • Imbalance of AA in the free pool, which increases the breakdown of proteins to provide more AA, and causes more AA excreted in urine
75
Q

Define a limiting amino acid.

A

The amino acid that is present in the lowest amount, relative to the body’s need for it, which limits protein synthesis

76
Q

What occurs to other amino acids if the quantity of the limiting amino acid is significantly lower?

A

Causes the catabolism of all the other amino acids present in “excess”, which slows growth and protein synthesis

77
Q

What occurs to nitrogen balance when a limiting amino acid is present?

A

Nitrogen balance is quite negative, as all the non-limiting amino acids are degraded

78
Q

Which amino acid is one of the most common limiting amino acids? Which types of individuals are more vulnerable?

A
  • Lysine

- Individuals consuming plant-protein and children

79
Q

Which amino acid reacts in cooking through the Maillard reaction? What does that cause?

A
  • Lysine

- Causes a lack of availability of lysine for protein synthesis

80
Q

What is the impact on increasing the availability of a limiting amino acid on amino acid catabolism, urinary nitrogen, and nitrogen balance?

A
  • Amino acid catabolism: decrease
  • Urinary nitrogen: decrease (still higher than the healthy nitrogen)
  • Nitrogen balance: less negative (getting closer to 0)
81
Q

What is the clinical and metabolic method to analyze nitrogen balance?

A
  • Diet must be adapted for a week minimum
  • Feces/urine must be collected for a minimum of 3 days
  • Involves a huge amount of subject commitment because crystalline amino acids taste bad
82
Q

How do miscellaneous losses influence protein requirement based on nitrogen balance?

A

Miscellaneous losses increase protein requirement

83
Q

What was the issue with nitrogen balance data in the 1950s?

A
  • They did not account for miscellaneous losses, which undershot the protein requirement
  • They did not possess modern statistical methods
84
Q

How did the re-analysis of the nitrogen balance data from the 1950s change in modern years?

A

By changing the modelling by using modern statistical methods

85
Q

How does the dose response curve of nitrogen retention change when an essential amino acid is limiting, at requirement, and in excess?

A
  • Limiting: nitrogen retention is negative when a amino acid is deficient
  • As the intake of the limiting amino acid is increased, the other AA are present in less of an excess, causing less urinary nitrogen, increasing nitrogen balance
  • At requirement: nitrogen balance is 0
  • Excess: nitrogen balance is 0
86
Q

What is nitrogen retention?

A

The percentage of dietary amino acids that are retained (0 in healthy adults)

87
Q

How does the dose response curve of direct oxidation change when an essential amino acid is limiting, at requirement, and in excess?

A
  • Limiting: low oxidation since the AA is used to make protein
  • As the intake increases, more protein can be synthesized, but the oxidation rate maintains a low plateau
  • At requirement: the limiting AA is now present in excess, which increases oxidation
  • Excess: every amount that we increase above requirement increases oxidation, and the labeled CO2 in the breath
88
Q

What are the three pros of measuring amino acid requirement through direct oxidation?

A

1) Following the carbon skeleton does not require long periods of adaptation to the urea pool
2) Does not require a huge participation commitment, and measurements are done rather easily (tracer infusion, breathe into a bag)
3) Receive test amino acids in a sterile solution

89
Q

What are the three cons of measuring amino acid requirement through direct oxidation?

A

1) Solely the branched-chain amino acids, lysine, and phenylalanine produce a labeled CO2 that may be utilized
2) Changing intake from a low amount to an excess of AA changes the AA pool, which may interfere with results
3) Analytical techniques are much more expensive than nitrogen balance

90
Q

Which amino acids produce a labeled carbon that may be utilized in direct oxidation?

A
  • Branched-chain amino acids (leucine, isoleucine, valine)
  • Lysine
  • Phenylalanine
91
Q

Why can’t you study very low intake of amino acids with direct oxidation?

A

Because of the non-negligible tracer

92
Q

What are the analytical techniques used for direct oxidation and indicator amino acid oxidation ?

A
  • Breath collection requires an isotope ratio mass spectrometer (IRMS) for CO2 enrichment
  • Calorimeter for CO2 production
  • Blood samples require a GC mass spectrometer (GCMS) for amino acid enrichment
93
Q

What do the direct oxidation and indicator amino acid oxidation methods require in terms of subject feeding?

A
  • Subjects must be in steady-state

- Constantly nibbling over the course of the day

94
Q

What is the concept behind the indicator amino acid oxidation (IAAO)?

A

When an indispensable amino acid is limiting, then all other indispensable amino acids will be oxidized, as amino acids CANNOT be stored

95
Q

Which indicator amino acid is usually used in indicator amino acid oxidation?

A

Phenylalanine

96
Q

How does the dose response curve of indicator amino acid oxidation change when a test amino acid is limiting, at requirement, and in excess?

A
  • Limiting: when the test amino acid is low, it severely limits protein synthesis, which means that the oxidation of all other amino acids are high (including the indicator)
  • As the intake increases, protein synthesis increases, but oxidation of the indicator still occurs
  • At requirement: the test amino acid is no longer limiting protein synthesis, so oxidation no longer occurs
  • Excess: a plateau is maintained, and past requirement, there is no change in protein synthesis or on the oxidation of other amino acids
97
Q

What is the minimally invasive IAAO model used for?

A

Model used to determine the amino acid requirements for sick children in a non-invasive way

98
Q

What is the tracer administration method for the minimally invasive IAAO model?

A
  • Repeated oral “nibbling” of tracer solution after 4 hour feeding equilibration
  • The child sips the tracer very slowly
99
Q

What are the sampling methods for the minimally invasive IAAO model?

A
  • Breath collection for CO2 enrichment

- Urine in place of blood for plasma amino acid enrichment (every half hour)

100
Q

How has lysine requirement changed?

A
  • From the 1950s to 2000s, the EAR was based on nitrogen balance studies (12 mg/kg/d)
  • The DRI committee re-measured the data through oxidation studies and determined that it was significantly higher (27 to 37 mg/kg/day)
  • The nitrogen balance studies were also re-analyzed using modern statistical approaches, and the requirement was also much higher (30 mg/kg/day)
101
Q

Which indispensable amino acid is not very present in dietary protein and has a low requirement as well?

A

Tryptophan

102
Q

How is the quality of protein determined?

A

By the amount of indispensable amino acids in a gram of protein

103
Q

What quantity of indispensable amino acids was thought to be necessary in protein according to WHO in 1985? What did the DRI report say?

A
  • WHO: 11mg/g of protein (10%)

- DRI Report: 285 mg/g of protein (30%)

104
Q

The quantity of indispensable amino acids consumed are particularly important for which group of people?

A

Individuals consuming a plant-based diet, or individuals that consume a low-variety diet

105
Q

Which amino acids are important and every day scenarios, and are likely to be limiting in diets?

A
  • Lysine
  • Tryptophan
  • Threonine
  • Cysteine
  • Methionine
106
Q

Which indispensable amino acid requirement was added in recent years?

A

Histidine

107
Q

How did a histidine-free diet for 48 days, followed by repletion, affect nitrogen balance, protein turnover, and phenylalanine indicator oxidation (IAAO)?

A
  • No effect on nitrogen balance
  • Decreased protein turnover
  • Decreased phenylalanine oxidation (IAAO)
108
Q

How did a histidine-free diet for 48 days, followed by repletion, affect the histidine free pool? What does that indicate?

A
  • Decreased the histidine free pool by half

- Indicates that there is an adaptation or a consequence produced by the diet

109
Q

What is hematocrit? What is it normally?

A
  • The fraction of blood volume composed of RBCs

- Normally, hematocrit is 49%

110
Q

How did a histidine-free diet for 48 days, followed by repletion, affect the hematocrit? What does that indicate?

A
  • Decreased hematocrit (43%)

- Indicates that there was a decrease in RBCs

111
Q

How did a histidine-free diet for 48 days, followed by repletion, affect the hemoglobin? What does that indicate?

A
  • Decreased hemoglobin

- Indicates that the individual is developing anemia

112
Q

How did a histidine-free diet for 48 days, followed by repletion, affect ferritin? What does that indicate?

A
  • Ferritin concentration increased

- Indicates that iron stores are increasing

113
Q

What is ferritin?

A
  • Iron is stored bound to ferritin in the liver

- The amount in plasma is an indicator of the quantity in the liver

114
Q

How did a histidine-free diet for 48 days, followed by repletion, affect transferrin? What does that indicate?

A
  • Transferrin concentration decreased

- Suggests that iron is more abundant

115
Q

How are transferrin stores altered in an individual deficient in iron?

A

Increased level of transferrin to increase absorption efficiency and transportation from stores

116
Q

How did a histidine-free diet for 48 days, followed by repletion, affect albumin? What does that indicate?

A
  • Albumin concentration decreased

- Indicates that there is a slowing down of protein synthesis, corroborated by the decrease in protein turnover overall

117
Q

What is the overall effect of histidine deficiency?

A
  • Decreased hemoglobin synthesis, which is high in histidine
  • Compromised ability to make RBCs and transport oxygen
  • This is NOT related to iron, but to a deficiency in histidine
118
Q

What are accommodations?

A

Serious adaptations to a deficiency, which indicate that there is a functional problem

119
Q

Which populations does histidine particularly affect?

A
  • Children

- Critical in long-term health

120
Q

What does histidine deficiency ressemble? How may they be differentiated?

A
  • Ressembles iron deficiency anemia, in which case the individual would be told to consume iron supplements
  • However, when they get re-tested, they would see that an iron supplement does not solve the functional issues of histidine deficiencies

Val 307 (15 decks)

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