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Kris 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 has 4 amino groups-> transferred to urea
- Arginine is used to make:
o Nitric oxide which dilates arteries and improves blood flow
o Polyamine synthesis – important for growth

• Glutamate is the metabolic source of energy for the intestines, since the intestines do not use glucose
o Glutamate is also required for the synthesis of Arginine/Citrulline and GSH
• Glutamate is glutamine with an extra amino group
o Its function is to transport amino groups away from the tissues to the liver where it will enter the urea cycle and be synthesized into urea (waste) to be excreted from the body.

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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 at steady state
    a. Eating small, equally times meals
  2. Homogeneity of pool
    a. The AA are equally distributed and blood plasma is a representative sample
    b. Usually artery sample
  3. Rate of inflow= rate of outflow
    a. Flow= tracer infusion rate/ tracer concentration in the pool
  4. Massless tracer, = tracee
  5. No tracer recycling
    a. Make sure that tracer cannot state behind once the labeled element has been used
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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

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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28
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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29
Q

What is the calculation for flow in a tracer dilution?

A

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

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30
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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31
Q

What are the two routes of amino acid intake?

A
  • Diet intake

- Proteolysis

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32
Q

What are the two routes of amino acid expenditure?

A
  • Protein synthesis

- Amino acid oxidation

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33
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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34
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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35
Q

What element incorporated into water forms heavy water?

A

Deuterium (2H)

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36
Q

What isotopes are preferred to be used as tracers?

A

Stable isotopes that are NON-radioactive

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37
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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38
Q

How does a GCMS function?

A

• Basically, a fancy oven where the temperature can be increased to 300 degrees C

  1. The sample is injected into the top of the column of the gas chromatograph
  2. The temperature inside the gas chromatograph can reach up to 300 degrees Celsius (acts as an oven). This high temperature converts the sample from its liquid/solid form to its gaseous form to pass through the gas chromatograph.
  3. When the gas sample reaches the separator, it encounters a vacuum pump, which has an air pressure inside of 1/1 billionth of the pressure outside of the machine. This allows for one molecule to pass through at a time.
  4. Then inside the mass spectrometer, the molecules of the sample pass through the ionizing source, which charges the molecules with a positive charge. The molecules of the sample are now positive ions.
  5. The positively charged ions are sent into a series of focusing lenses where there is a negatively charged voltage to attract the positive ions and make them move through one by one through the series of magnifying lenses.
  6. Then, the positively charged ions will encounter the “quadrupole mass analyzer” that consists of negatively charged voltage rods.
  7. Only certain molecules with a particular mass are able to pass through the rods, the others accumulate on the outside of the rods.
  8. These molecules will spiral on the rods and hit a detector at the end that will determine their mass.
  9. Then, the rods can be moved further apart to allow new molecules of particular mass to pass through and their mass to be detected by the detector at the end.
  10. The information is sent to a data system and is displayed.
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39
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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40
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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41
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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42
Q

What is a keto acid?

A

An amino acid without the amino group

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43
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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44
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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45
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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46
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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47
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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48
Q

What is the metabolic fuel for the gut?

A

Glutamate

49
Q

What is glutamine? How does it compare to glutamate?

A

Glutamine is a glutamate with an extra amino group

50
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

51
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
52
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

53
Q

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

A

The gut uses oxidized glutamate as a metabolic fuel

54
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

55
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
56
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
57
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

58
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
59
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

60
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

61
Q

What percentage nitrogen is protein by weight?

A

Protein is 16% nitrogen by weight

62
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

63
Q

What is the formula for nitrogen balance?

A

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

64
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

65
Q

What factors account for miscellaneous losses?

A
  • Sweat
  • Hair
  • Fingernails
66
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

67
Q

What does “Apparent Nitrogen Balance” mean?

A

That miscellaneous losses are not considered

68
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

69
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

70
Q

What is hypermetabolic positive nitrogen balance?

A
  • Synthesis > breakdown

- Child growing and catching up from malnutrition

71
Q

What is hypometabolic positive nitrogen balance?

A
  • Synthesis > breakdown

- Elderly person that is trying to recover from an illness

72
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
73
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
74
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

75
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

76
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

77
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

78
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

79
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)
80
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
81
Q

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

A

Miscellaneous losses increase protein requirement

82
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
83
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

84
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
85
Q

What is nitrogen retention?

A

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

86
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
87
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

88
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

89
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
90
Q

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

A

Because of the non-negligible tracer

91
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
92
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

93
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

94
Q

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

A

Phenylalanine

95
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
96
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

97
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
98
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)

99
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)
100
Q

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

A

Tryptophan

101
Q

How is the quality of protein determined?

A

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

102
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%)

103
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

104
Q

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

A
  • Lysine
  • Tryptophan
  • Threonine
  • Cysteine
  • Methionine
105
Q

Which indispensable amino acid requirement was added in recent years?

A

Histidine

106
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)
107
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

108
Q

What is hematocrit? What is it normally?

A
  • The fraction of blood volume composed of RBCs

- Normally, hematocrit is 49%

109
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

110
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

111
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

112
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

113
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

114
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

115
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

116
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
117
Q

What are accommodations?

A

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

118
Q

Which populations does histidine particularly affect?

A
  • Children

- Critical in long-term health

119
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

Kris 307 (19 decks)

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