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MEH * > S1 Protein and Amino Acid Metabolism > Flashcards

S1 Protein and Amino Acid Metabolism Flashcards

1
Q

What are the two key concepts of nitrogen metabolism?

A
  1. Nitrogen balance

2. Protein turnover

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2
Q

What is creatinine?

A
  • breakdown product of creatine and creatine phosphate in muscle
  • a clinical marker for muscle mass and renal function
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3
Q

How is creatinine a clinical marker for muscle mass and renal function?

A
  1. Muscle mass - produced at a constant rate depending on muscle mass
  2. Renal function - filtered via kidneys into urine, if a lower level than norm present in urine, sign of renal damage
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4
Q

What are the three types of nitrogen balance?

A
  1. N equilibrium (intake = output) - the norm
  2. Positive N balance (intake > output) - norm in growth and pregnancy or malnutrition recovery
  3. Negative N balance (intake < output) - never the norm, caused by trauma, infection or malnutrition
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5
Q

What is protein turnover?

A
  • Breakdown of older proteins, replaced by new proteins.
  • Free amino acids from digestion, new (de novo) amino acid synthesis, proteolysis
  • Free amino acids used to synthesis cellular proteins, processed by the liver (broken down to carbon skeleton - used for energy ad amino group - excreted)
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6
Q

After the liver has processed free amino acids, what is the carbon skeleton used for?

A

Dependent on the amino acid (it’s side chain) the carbon skeleton becomes a glucogenic amino acid (gluconeogenesis) or a ketogenic amino acid (ketone bodies). Both of which produce energy

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7
Q

What happens to the amino group of an amino acid after liver metabolism?

A

Amino group —> urea —> urine

  • amino group can form ammonia (toxic) so mechanisms are in place to remove ammonia - converted to urea in mammals
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8
Q

Give 3 examples of glucogenic amino acids.

A
  1. Alanine
  2. Glycine
  3. Aspartate
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9
Q

Give 3 examples of ketogenic amino acids.

A
  1. Lysine
  2. Leucine
  3. Tyrosine (also glucogenic)
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10
Q

When are protein reserves used as fuel/energy? How is it mobilised?

A

During extreme stress e.g. starvation

Mobilised by hormone control

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11
Q

Which hormones increase/decrease protein synthesis and protein degradation?

A

Protein synthesis - increased by insulin and growth hormone, decreased by glucocorticoids

Protein degradation - increased by glucocorticoids, decreased by insulin and growth hormone

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12
Q

What is an example of a glucocorticoids?

A

Cortisol

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13
Q

What is Cushing’s syndrome?

A

Excessive breakdown of protein due to excess cortisol - weakens the skin structure leading to striae formation

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14
Q

What are the 9 essential amino acids?

A
  1. Isoleucine
  2. Lysine
  3. Threonine
  4. Histidine
  5. Leucine
  6. Methionine
  7. Phenylalanine
  8. Tryptophan
  9. Valine
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15
Q

What 3 amino acids become essential in kids and pregnant women? And why?

A
  1. Arginine
  2. Tyrosine
  3. Cysteine

Because they have a higher rate of protein synthesis

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16
Q

Are proteins from animal origin or plant origin higher quality?

A

Animal origin - contain all essential amino acids (plant origin are usually deficient in one or more essential amino acid)

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17
Q

In what 3 pathways can non-essential amino acids be synthesised?

A
  1. Intermediates of glycolysis
  2. Pentose phosphate pathway
  3. Krebs cycle
18
Q

Some amino acids are required for synthesis of important compounds, what can tyrosine, cysteine, tryptophan, histidine, glutamate, glycine, arginine and serine be used to synthesise?

A
  1. Tyrosine - thyroid hormones, melanin, catecholamines
  2. Cysteine - glutathione (GSH/GSSG)
  3. Tryptophan - serotonin (5HT), melatonin
  4. Histidine - histamine
  5. Glutamate - GABA
  6. Glycine - glutathione, creatine, haem
  7. Arginine - nitric oxide (NO)
  8. Serine - sphingosine
19
Q

How is nitrogen removed from amino acids (2 ways)?

A
  1. Transamination

2. Deamination

20
Q

Why do you remove the amino group from an amino acid?

A

Allows the carbon skeleton to be utilised in oxidative metabolism

21
Q

What is transamination?

A

A chemical reaction that transfers an amino group to a ketoacid (from a amino acid) to form new amino acids

E.g. use of alpha-ketoglutarate (ketoacid) to transfer the amino group

22
Q

What are the two aminotransferase enzymes?

A
  1. Alanine aminotransferase (ALT) - converts alanine to glutamate
  2. Aspartate aminotransferase (AST) - converts glutamate to aspartate
23
Q

What organ function test are plasma levels of ALT and AST measured?

A

Liver function test - levels higher in conditions that cause cellular necrosis e.g. viral hepatitis, autoimmune liver diseases and toxic injury

24
Q

What is deamination?

A

Amino group lost from amino acid (forming a ketoacid) and forms ammonia.

Ketoacids can be utilised for energy.

The ammonia is toxic so is converted to urea and excreted in urine.

25
Q

Where does deamination occur?

A

Liver and kidney

26
Q

What 3 enzymes deaminate amino acids?

A
  1. Amino acid oxidases
  2. Glutaminase
  3. Glutamate dehydrogenase
27
Q

What is ammonia converted into at physiological pH?

A

Ammonium ions (NH4+)

28
Q

What is urea? What is it like?

A
  • has a high nitrogen content
  • non-toxic
  • water soluble
  • chemically inert in humans
  • excreted in urine via kidneys
  • osmotic role in kidney tubules
29
Q

What is the urea cycle?

A

Occurs in the liver and involved 5 enzymes (the cycle is regulated on demand, it depends on the level of protein metabolism (related to need to dispose of ammonia))

30
Q

What is refeeding syndrome?

A

When lots of highly nutritional/high protein content food is given to severely malnourished patients - leads to a sudden shift in electrolytes that help your body metabolise food.

31
Q

What defects can occur in the urea cycle?

A
  • autosomal recessive genetic disorders caused by deficiency of an enzyme in the urea cycle
  • mutations causing partial loss of enzyme function
  1. Hyperammonaemia (excess ammonia in the blood)
  2. Accumulation/excretion of urea cycle intermediates
32
Q

How do you manage defects in the urea cycle?

A

Have a low protein diet and replace amino acids in your diet with ketoacids (less amino groups needing to be fed into urea cycle)

33
Q

What are symptoms of defects in urea cycle?

A

Vomiting, lethargy, irritability, seizures, coma and mental retardation

(VLISCR

RISCLIV)

34
Q

How is ammonia toxic to the body?

A
  1. Interferes with amino acid transport and protein synthesis
  2. Makes pH more alkaline
  3. Alteration of blood-brain barrier
  4. Interference with TCA cycle (reacts with alpha-ketoglutarate forming glutamate)
35
Q

What two mechanisms are used for the safe transport of amino acid nitrogen from tissues to the liver for disposal?

A
  1. Glutamine - ammonia + glutamate = glutamine, transported in the blood, cleaved by glutaminase, ammonia fed into urea cycle from liver to kidneys. Glutamine has two amino groups so an efficient transporter.
  2. Alanine - glutamate gains amino group by transamination, then Pyruvate transaminated by glutamate to form alanine, transported in blood, converted back to pyruvate in the liver (transamination), amino group fed into urea cycle via glutamate.
36
Q

What is phenylketonuria (PKU)?

A

Caused by deficiency in phenylalanine hydroxylase (autosomal recessive).

Leads to an accumulation of phenylalanine in tissues, plasma and urine - have phenylketones in urine (test this) and urine has a musty smell.

Have a diet high in tyrosine (tyrosine usually produced from phenylalanine) and low in phenylalanine

37
Q

Can most among acid metabolism diseases be avoided with early intervention?

A

Yes - babies have the heel prick test to test for these metabolism errors

38
Q

What is a main symptom of amino acid metabolism diseases?

A

Intellectual impairment

39
Q

What is homocystinuria?

A

Problems with breaking down methionine leads to excess homocysteine (autosomal recessive) - defect in cystathionine beta-synthase.

Treat with a low methionine diet, supplement cysteine into diet as it’s not made

40
Q

Elevated plasma levels of homocysteine can be associated with what type of disease?

A

Cardiovascular disease

MEH * (22 decks)

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