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Physiology 334 - protein metabolism > Lecture 3 - Metabolic role of amino acids > Flashcards

Lecture 3 - Metabolic role of amino acids Flashcards

1
Q

Amino acids: major roles in metabolism

Metabolismfor ATP synthesisto maintain function-to maintain cell/organ/organism viability

A
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2
Q

What metabolism can do:

A

glucose, obesity, fasting /longevity

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3
Q
A
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4
Q

Contributions towards ATP

A

Different cells are different!
What is the substrate?
Is there a substrate preference?
What are pathway activities/reliance?
What is the oxygen availability?

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5
Q

Amino acids: more than a potential substrate

A
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6
Q

Each cell type has an upper limit for protein storage

A

(defined by its genetic profile)
e.g. skeletal muscle fiber vs erythrocyte

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7
Q

Excess amino acids are

A

degraded and used for ATP production or converted to fat or glycogen and stored (kidney, liver, mucosa)

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8
Q

Amino acid supplements in body building…
–> fat and glycogen (unless Δ in metabolic demand)

A
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9
Q

Amino acids for protein synthesis: cell specific

A

Genetic make-up controls protein expression profile (proteins control gene expression profile-downward causation)

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10
Q

Requirements for protein synthesis:

A
  1. Synthesis of the amino acids (availability)
  2. Appropriate amino acid conjugation
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11
Q

Availability of amino acids

A

10 amino acids can be synthesized (non-essential), 10 cannot/or in quantities that do not match organisms demand (essential)

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12
Q

Essential amino acids:

A

threonine, methionine, valine, leucine, isoleucine, lysine, arginine, phenylalanine, trypotophan, histidine

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13
Q

Also the non-essential amino acids are essential

A
  1. All or non function of amino acids in protein synthesis: if a single required amino acid is not available, the WHOLE protein cannot be synthesized!
  2. The protein synthesis and its magnitude is limited to the level of the lowest quantity of a specific amino acid
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14
Q

Synthesis of the nonessential amino acids

A
  • Depends on the formation of the appropriate α-keto acid
    Eg: pyruvic acid (glycolysis) keto acid precursor for alanine
  • Transamination
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15
Q

Transamination

A

amino radical transferred to the keto acid, the keto oxygen is transferred to amino radical donor
- is key for mitochondrial functioning

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16
Q

Transamination enzyme:

A

transaminases (ALAT, ASAT)

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17
Q

Key amino acidsin metabolism

A
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18
Q
A
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19
Q
A
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20
Q

Protein catabolism for ATP

A

Most amino acids used for ATP synthesis come not from protein catabolism but from surplus amino acids in diet

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21
Q

To make amino acids metabolically favorable, they need to

A

be deaminated!

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22
Q

Degradation for energy or storage as fat

A

Degradation begins with the process of deamination:
1. via transamination
2. via oxidative deamination

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23
Q

Generation of urea

A
  • NH3
  • ammonia is toxic
  • if liver is dysfunctional = high levels of ammonia
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24
Q

Aquatic animals simply excrete ammonia

A

ammonotelic

25
Q

Generation of urea: Where no/less water available:

A

conversion into less toxic products: urea (terrestrial vertebrates-ureotelic),

26
Q

uric acid

A

(birds and reptiles-uricotelic)

27
Q

Rapid removal from blood to form urea in the liver
All urea formed is synthesized in the liver (hepatic disease)
Urea cycle (urea renal excreted)

A
28
Q

the main transport vehicle for nitrogen

A

Glutamine

29
Q

Amino groups are transferred to α-ketoglutarate, forming glutamate, which in turn can accept more nitrogen forming glutamine. Glutamine: aminoradical donor + store house

A
30
Q

Once de-aminated 3 valuable metabolic pathways exist

A
  • TCA cycle
  • Gluconeogenesis (liver and kidney, not muscle!)
  • Acetyl-CoA –> fatty acid synthesis or ketogenesis (acetoacetic acid)
31
Q

The central metabolic role of alanine

A

Alanine transaminated to pyruvate
Pyruvate oxidized to acetyl-CoA
Pyruvate carboxylated to oxalacetate

Aspartate + α-ketoglutarate<–> oxaloacetate + glutamate (AST or ASAT)

32
Q

The central metabolic role of oxaloacetate

A

Condenses with acetyl-CoA to form citrate
Can be generated from cytoplasmic citrate (lyase)
Can be transported as malate
Transaminated to aspartate vs generated from aspartate

Aspartate + α-ketoglutarate <–> oxaloacetate + glutamate (AST or ASAT)

33
Q

Amino acids as fuel substrates: plentiful, multiple entry points in TCA cycle

A

Ketogenic amino acids
Glucogenic amino acids

34
Q

Entry points of glucogenic and ketogenic amino acids

A

Branched-chain amino acids

35
Q

Every entry point stands in some relationship with an amino acid exchange or transaminase system!

A
36
Q

Amino acids and indirect role for mitochondrial respiration:

A
  • Malate/Aspartate shuttle

Aspartate + α-ketoglutarate <–> oxaloacetate + glutamate (AST or ASAT) and its relation to malate

Transport of reducing equivalents to mitochondria

37
Q

More entry points than anticipatedmaintaining and modulating TCA cycle flux AND providing metabolites

A
38
Q

Amino acid oxidation: oxygen sparing

A
  • very efficient way to make ATP
39
Q

Failure in protein metabolism
= Failure in mitochondria (and vice versa)
- proteins start to aggregate = disfunction = parkinsons

A
40
Q

Neurodegenerative disease if mutation in malate/ aspartate shuttle

A
41
Q

AA’s can control TCA cycle, How?

A

By providing keto and glycogenic amino acids as fule/substrates
(good substrate for ATP production)

42
Q

Amino acids –> pyruvate –> glucose

A
  • gluconeogenesis
  • 2 organs only: liver and kidney!

AA’s are taken up in the mucosa –> liver and kidneys –> preserves glucose levels (via gluconeogenesis)

43
Q

Protein: large energy store
- Gets to brain through plasma - Thus also maintains plasma levels

A
44
Q
A
45
Q
A
46
Q

Protein metabolism: an underestimated and neglected metabolic role player?

A

Contribution as substrates
Intermediary metabolism: TCA cycle flux
Gluconeogenesis
Oxygen efficiency and ATP yield
Malate shuttle for transport of reducing equivalents in mitochondrial respiration

47
Q

Problem: 1. “unseen” amino acids: difficulty of measuring (radioactive tracer), inhibition of enzymes, protein synthesis, ATP consumption

A
  • Dont know how much ATP a cell actually uses –> would have to inhibit something and measure decline in ATP use
48
Q

Problem 2: Intracellular vs extracellular (plasma amino acids)

A
  • How proteins absorbed/ transported and then what happens intracellularly
    (2 different processes)
49
Q

AA’s can be rapidly degraded (and made available) in big amounts.

A
50
Q

Obligatory protein degradation

A
  • 0-30 g protein/day is degraded, deaminated and oxidized
  • To prevent net loss: 75 g protein intake/day is recommended
  • If one amino acid is missing in the diet, the others become unusable  failure in protein synthesis
  • diet (complete vs incomplete proteins)
    High carb diet = high insulin levels = cell cant undergo protein degradation
51
Q

Hormones that regulate protein metabolism

A
  • Growth hormone
  • Insulin
  • Glucocorticoids
  • Testosterone
  • Thyroxine
52
Q

Growth hormone:

A

increase in protein synthesis rate

53
Q

Insulin

A

is required for protein synthesis (lack of insulin decreases protein synthesis to almost 0); accelerate amino acid transport/uptake; by providing glucose, it spares amino acids from oxidation

54
Q

Glucocorticoids:

A

increase in [amino acid] plasma; breakdown of extrahepatic proteins; important for aminoacid drived gluconeogenesis and ketogenesis

55
Q

Testosterone:

A

increased deposition of protein, especially contractile proteins in muscle

56
Q

Thyroxine:

A

depending on substrate availability it contributes to protein degradation or protein synthesis

57
Q

Glucocorticoids increase amino acid availability

A
58
Q

Thyroxin: increase amino acid availability or protein synthesis depending on metabolite availability

A
59
Q

4 Thinking points
Amino acids as substrates (fuel for the metabolic engine)

Amino acids in intermediary metabolism (oil in the metabolic engine)

Amino acids and the nitrogen waist issue

Intracellular availability under normal conditions

A

Physiology 334 - protein metabolism (13 decks)

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