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Semester 2-MEH > Session 3-Protein And AA Metabolism > Flashcards

Session 3-Protein And AA Metabolism Flashcards

1
Q

What is creatinine the breakdown product of?

A

Creatine

Creatine phosphate

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2
Q

True or false: creatinine urine excretion over 24 hours is proportional to muscle mass

A

TRUE

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3
Q

What is creatinine commonly used as an indicator of?

A

Renal function

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4
Q

What is the normal state of nitrogen balance in an adult?

A

N equilibrium, intake=output

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5
Q

What is the normal state of nitrogen balance in growth and pregnancy or in an adult recovering from malnutrition?

A

Positive N balance, intake>output

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6
Q

Which state of nitrogen balance is never normal and what are its causes?

A

Negative N balance, intake < output

Trauma, infection and malnutrition

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7
Q

What is protein turnover?

A

Proteins undergo continuous breakdown and resynthesis

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8
Q

What does the rate of protein turnover depend on?

A

Depends on the protein and varies during growth (fast) and ageing (slows)

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9
Q

True or false: normally the rate of protein breakdown equals the rate of resynthesis

A

TRUE

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10
Q

What effect do insulin and growth hormone have on protein synthesis?

A

Increases protein synthesis

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11
Q

What effect does cortisol have on skeletal muscle?

A

Promotes breakdown of muscle protein (proteolysis) and release of AA

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12
Q

When an AA is catabolised and an amino group is removed, what is it converted to?

A

Urea, excreted from the body in urine

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13
Q

After an amino group has been removed from an AA, what can the remaining C-skeleton be converted to? (6)

A 
Pyruvate
Oxaloacetate 
Fumarate 
Alpha-ketoglutarate
Succinyl-CoA
Acetyl-CoA
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14
Q

What are ketogenic amino acids?

A

AA that produce acetyl-CoA because acetyl-CoA can be used to produce ketone bodies

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15
Q

Name two ketogenic AA

A

Lysine

Leucine

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16
Q

What are glucogenic AAs?

A

AAs that give rise to the other products of C-skeleton conversion as they can be used for glucose synthesis by gluconeogenesis

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17
Q

Name an AA which is both glucogenic and ketogenic

A 
Isoleucine 
Threonine 
Phenylalanine 
Tyrosine 
Tryptophan
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18
Q

What effect do insulin and growth hormone have on protein degradation?

A

Decreases

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19
Q

What effect do glucocorticoids (cortisol) have on protein synthesis?

A

Decreases

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20
Q

What effect do glucocorticoids (cortisol) have on protein degradation?

A

Increases

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21
Q

In which condition can excessive protein breakdown occur and this can lead to the formation of what?

A

Cushing’s syndrome (excess cortisol)

Weakens skin structure, leading to the formation of striae

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22
Q

Where do the carbon atoms for non-essential AA synthesis come from?

A

Intermediates of glycolysis
Pentose phosphate pathway
Krebs cycle

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23
Q

Where does the amino group for AA synthesis come from?

A

Form other AA by transamination or from ammonia

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24
Q

Why is the removal of an amino group from an AA essential?

A

To allow carbon skeleton to be utilised in oxidative metabolism

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25
Q

What are the two main pathways that facilitate the removal of nitrogen from AA?

A

1) transamination

2) deamination

26
Q

Which enzymes are involved in transamination?

A

Aminotransferases (transaminases)

27
Q

What do aminotransferase enzymes use to funnel the amino group to glutamate?

A

Alpha-ketoglutarate

28
Q

What does aspartate aminotransferase (AST) convert?

A

Glutamate to aspartate

29
Q

Which coenzyme do all aminotransferases require?

A

Pyridoxal phosphate (derivative of vitamin B6)

30
Q

What does alanine aminotransferase (ALT) convert?

A

Alanine to glutamate

31
Q

When are plasma ALT and AST levels measured?

A

Part of liver function test

32
Q

When are levels of plasma ALT and AST high?

A

In conditions that cause extensive cellular necrosis such as:
Viral hepatitis
Autoimmune liver disease
Toxic injury

33
Q

What is deamination?

A

Liberation of an amino group as free ammonia, mainly in liver and kidney

34
Q

What are L and D-amino acid oxidases?

A

Low specificity enzymes that convert AA to keto acids and ammonia

35
Q

Which cells have a high activity of D-amino acid oxidase?

A

Liver cells

36
Q

How do D-amino acids enter through the diet?

A

Found in plant and bacterial cell

37
Q

Why must D-amino acids not be used for protein synthesis?

A

Proteins would be structurally abnormal and non-functional as the enzyme converts them to keto acids that aren’t optically active

38
Q

Which enzymes can deaminate AA? (3)

A

Amino acid oxidases (L and D)
Glutaminase
Glutamate dehydrogenase

39
Q

What is ammonia rapidly converted to at physiological pH?

A

Ammonium ion (NH4+)

40
Q

True or false: urea is not soluble in water

A

FALSE - extremely water soluble

41
Q

True or false: urea is chemically inert in humans

A

TRUE - bacteria can break it down to release ammonia

42
Q

Where do the amino groups of urea come from?

A

NH4+ and aspartate

43
Q

Where does the urea cycle occur and how many enzymes are involved in it?

A

In liver

5 enzymes

44
Q

True or false: low protein diet induces enzyme levels in the urea cycle

A

FALSE - high protein diet induces enzyme levels

45
Q

True or false: the urea cycle is inducible but not regulated

A

TRUE

46
Q

What is refeeding syndrome?

A

When nutritional support is given to severely malnourished patients - too much protein leads to hyperammonaemia

47
Q

What do defects in the urea cycle lead to?

A

Autosomal recessive genetic disorders caused by deficiency of one of enzymes in the cycle, leading to hyperammonaemia and the accumulation/excretion of urea cycle intermediates

48
Q

What are the symptoms of urea cycle disorders?

A 
Vomiting 
Lethargy
Irritability
Mental retardation
Seizures
Coma
49
Q

What is the management methods for urea cycle disorders?

A

Low protein diet

Replace AA in diet with keto acids

50
Q

True or false: ammonia is readily diffusible and very toxic to the brain

A

TRUE

51
Q

How is glutamine used in the disposal of ammonia?

A

ammonia combines with glutamate to form glutamine, which is transported to liver or kidneys where it is cleaved by glutaminase to reform glutamate and ammonia. In liver, ammonia fed into urea cycle and in kidney is excreted directly in urine

52
Q

How is alanine used to dispose of ammonia?

A

Ammonia combines with pyruvate to form alanine.
Alanine is transported to liver where it is converted back to pyruvate by transamination.
Amino group fed via glutamate into urea cycle -> urea.

53
Q

When is a heel prick test used?

A
  • Sickle cell disease
  • Cystic fibrosis
  • Congenital hyperthyroidism
54
Q

What is phenylketonuria (PKU)?

A

Autosomal recessive condition - deficiency in phenylalanine hydroxylase

55
Q

What does PKU lead to an accumulation of and what does this lead to?

A

Phenylalanine in tissue, plasma and urine -> phenylketones in urine

56
Q

What are the symptoms of PKU?

A 
Severe intellectual disability
Developmental delay
Microcephaly (small head)
Seizures
Hypopigmentation
57
Q

How can PKU be treated?

A

1) controlled low phenylalanine diet
2) avoid artificial sweeteners
3) avoid high protein foods such as meat, milk and eggs

58
Q

What is homocystinuria?

A

Autosomal recessive - problem with breaking down methionine so excess homocystine (oxidised form of homocysteine) excreted in urine

59
Q

What is the most common deficiency in homocystinuria?

A

Cystathionine beta-synthase

60
Q

What homocystinuria affect?

A

Connective tissue
Muscles
CNS
CVS

61
Q

How can homocystinuria be treated?

A

1) low methionine diet
2) avoid milk, meat, fish, cheese, eggs, nuts and peanut butter
3) cysteine, vitamin B6, Betaine, B12 and folate supplement

62
Q

Name an AA that is glucogenic

A 
Any one of the following:
Alanine
Glycine 
Threonine
Cysteine
Serine
Arginine
Proline
Histidine
Glutamine
Methionine
Valine
Aspartate
Asparagine

Semester 2-MEH (21 decks)

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