Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MEH > 1.2 - Protein And Amino Acid Metabolism > Flashcards

1.2 - Protein And Amino Acid Metabolism Flashcards

1
Q

Name 3 major nitrogen containing compounds

A

Amino acids
Proteins
Purines + Pyrimidines (DNA / RNA)

Smaller amounts of others – e.g.
• Porphyrins (haem) • Creatine phosphate • Neurotransmitters (e.g. dopamine) • Some hormones (e.g. adrenaline)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the function of creating and creating phosphate?

A

To provide short term energy supply in muscle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How is creatinine formed?

A

Formed as a breakdown product of creatinine and creating phosphate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Why is it useful to measure creatinine levels in urine?

A

Creatinine content of urine over 24 hours is proportional to muscle mass. Therefore by measuring we can estimate of muscle mass. Usually released at a constant rate. During muscle wastage, rate of creatinine production would increase. Commonly used as an indicator of renal function, raised creatinine in urine on damage to nephrons as kidneys usually accurately expel creatinine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a nitrogen balance?

A

A comparison of the nitrogen consumed in our diet through protein vs the nitrogen lost from our body through loss of skin/hair/nails and nitrogen containing waste products in faeces and urine.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is nitrogen equilibrium?

A

Nitrogen Intake = nitrogen output

No change in total body protein. Normal state in adult

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a positive nitrogen balance?

A

Nitrogen Intake > nitrogen output

Increase in total body protein. Normal state in growth & pregnancy or in adult recovering from malnutrition.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is a negative nitrogen balance?

A

Intake < output

Net loss of body protein. Never normal. Causes include trauma, infection, or malnutrition.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How much nitrogen is usually consumed each day?

A

16g

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the first stage in the catabolism of proteins?

A

Enzymes (proteases and peptidases) hydrolyse peptide bonds to release free amino acids in the gastrointestinal tract. Amino acids are then absorbed into the circulation.
Excess amino acids are broken down in stage 2 of protein catabolism.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the largest food store in an average man?

A

Triacylglycerol (15 kg)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

When is muscle protein used as a fuel?

A

During prolonged starvation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why are purple striae seen in Cushing’s syndrome?

A

There is excessive breakdown of protein due to excess cortisol. This weakens skin structure and leads to striae formation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How are free circulating amino acids used?

A

For synthesis of protein and other nitrogen containing compounds (purines, creative, haem).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What tissues uptake amino acids?

A

Skeletal muscle
Adipose tissue
Liver

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What regulates protein synthesis?

A

Insulin

Growth hormones

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What hormone stimulates proteolysis?

A

Cortisol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Describe the second stage of protein catabolism after amino acids have been freed.

A

Amino group is removed and converted to urea (CO(NH2)2) which is excreted in urine.
Reminding carbon skeletons are converted to acetyl-CoA, pyruvate, oxaloacetate, fumurate and other products that can be used for glycolysis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the difference between a ketogenic and glucogenic?

A

Ketogenic amino acids (leucine and lysine) produce acetyl-CoA which is used to synthesise ketone bodies

Glucogenic amino acids give rise to other products such as Pyruvate and oxaloacetate which can be used for gluconeogenesis.

Some amino acids can be both ketogenic and gluconeogenic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How does nitrogen leave the body?

A

In hair/nails/skin

In urea, ammonia, uric acid and creatinine in urine.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How are proteins generated when required?

A

Synthesised from free amino acids, protein is not stored.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What factors influence the rate of protein turnover?

A

The type of protein
Age
Periods of growth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Where does the second stage of protein catabolism occur?

A

In the liver.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Where do carbon atoms for non-essential amino acid synthesis come from?

A

Intermediates of glycolysis
Pentose phosphate pathway
Kreps cycle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How many amino acids are in the human body?

A

20

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

How do amino acid structures vary?

A

According to the side chain R

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the amino acid pool?

A

Total free amount of amino acids in the body and is 100g in the average male.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is normal fasting concentration of amino acids in the blood?

A

3mm/L

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What are non-essential amino acids?

A

Amino acids that can be synthesised by the body, with carbon atoms from intermediates of metabolic pathways and amino group from othe amino acids by the process of transamination or from ammonia.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What happens to excess amino acids?

A

Enter stage 2 catabolism to be converted into intermediates of carbohydrate or lipid metabolism or oxidised to produce energy as cannot be stored or excreted.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What are essential amino acids?

A

Amino acids that cannot be synthesised by the body.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Name the 9 essential amino acids

A 
Isolyeucine
Lysine
Threonine
Histidine
Leucine
Methionine 
Phenylalanine
Tryptophan
Valine

If learned, this huge list may prove truly valueable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Name 3 major nitrogen containing compounds

A

Amino acids
Proteins
Purines + Pyrimidines (DNA / RNA)

Smaller amounts of others – e.g.
• Porphyrins (haem) • Creatine phosphate • Neurotransmitters (e.g. dopamine) • Some hormones (e.g. adrenaline)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is the function of creating and creating phosphate?

A

To provide short term energy supply in muscle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

How is creatinine formed?

A

Formed as a breakdown product of creatinine and creating phosphate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Why is it useful to measure creatinine levels in urine?

A

Creatinine content of urine over 24 hours is proportional to muscle mass. Therefore by measuring we can estimate of muscle mass. Usually released at a constant rate. During muscle wastage, rate of creatinine production would increase. Commonly used as an indicator of renal function, raised creatinine in urine on damage to nephrons as kidneys usually accurately expel creatinine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What is a nitrogen balance?

A

A comparison of the nitrogen consumed in our diet through protein vs the nitrogen lost from our body through loss of skin/hair/nails and nitrogen containing waste products in faeces and urine.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

What is nitrogen equilibrium?

A

Nitrogen Intake = nitrogen output

No change in total body protein. Normal state in adult

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What is a positive nitrogen balance?

A

Nitrogen Intake > nitrogen output

Increase in total body protein. Normal state in growth & pregnancy or in adult recovering from malnutrition.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What is a negative nitrogen balance?

A

Intake < output

Net loss of body protein. Never normal. Causes include trauma, infection, or malnutrition.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

How much nitrogen is usually consumed each day?

A

16g

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

What is the first stage in the catabolism of proteins?

A

Enzymes (proteases and peptidases) hydrolyse peptide bonds to release free amino acids in the gastrointestinal tract. Amino acids are then absorbed into the circulation.
Excess amino acids are broken down in stage 2 of protein catabolism.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

What is the largest food store in an average man?

A

Triacylglycerol (15 kg)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

When is muscle protein used as a fuel?

A

During prolonged starvation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

Why are purple striae seen in Cushing’s syndrome?

A

There is excessive breakdown of protein due to excess cortisol. This weakens skin structure and leads to striae formation.

46
Q

How are free circulating amino acids used?

A

For synthesis of protein and other nitrogen containing compounds (purines, creative, haem).

47
Q

What tissues uptake amino acids?

A

Skeletal muscle
Adipose tissue
Liver

48
Q

What regulates protein synthesis?

A

Insulin

Growth hormones

49
Q

What hormone stimulates proteolysis?

A

Cortisol

50
Q

Describe the second stage of protein catabolism after amino acids have been freed.

A

Amino group is removed and converted to urea (CO(NH2)2) which is excreted in urine.
Reminding carbon skeletons are converted to acetyl-CoA, pyruvate, oxaloacetate, fumurate and other products that can be used for glycolysis

51
Q

What is the difference between a ketogenic and glucogenic?

A

Ketogenic amino acids (leucine and lysine) produce acetyl-CoA which is used to synthesise ketone bodies

Glucogenic amino acids give rise to other products such as Pyruvate and oxaloacetate which can be used for gluconeogenesis.

Some amino acids can be both ketogenic and gluconeogenic

52
Q

How does nitrogen leave the body?

A

In hair/nails/skin

In urea, ammonia, uric acid and creatinine in urine.

53
Q

How are proteins generated when required?

A

Synthesised from free amino acids, protein is not stored.

54
Q

What factors influence the rate of protein turnover?

A

The type of protein
Age
Periods of growth

55
Q

Where does the second stage of protein catabolism occur?

A

In the liver.

56
Q

Where do carbon atoms for non-essential amino acid synthesis come from?

A

Intermediates of glycolysis
Pentose phosphate pathway
Kreps cycle

57
Q

How many amino acids are in the human body?

A

20

58
Q

How do amino acid structures vary?

A

According to the side chain R

59
Q

What is the amino acid pool?

A

Total free amount of amino acids in the body and is 100g in the average male.

60
Q

What is normal fasting concentration of amino acids in the blood?

A

3mm/L

61
Q

What are non-essential amino acids?

A

Amino acids that can be synthesised by the body, with carbon atoms from intermediates of metabolic pathways and amino group from othe amino acids by the process of transamination or from ammonia.

62
Q

What happens to excess amino acids?

A

Enter stage 2 catabolism to be converted into intermediates of carbohydrate or lipid metabolism or oxidised to produce energy as cannot be stored or excreted.

63
Q

What are essential amino acids?

A

Amino acids that cannot be synthesised by the body.

64
Q

Name the 9 essential amino acids

A 
Isolyeucine
Lysine
Threonine
Histidine
Leucine
Methionine 
Phenylalanine
Tryptophan
Valine

If learned, this huge list may prove truly valueable

65
Q

What are conditionally essential amino acids?

A

Arginine tyrosine cysteine

Only essential during high rates of protein synthesis (children + pregnant women)

66
Q

Why are vegan diets prone to essential amino acid deficiencies?

A

Protein of plant origin maybe deficient in one or more essential amino acids.

67
Q

How are amino groups removed from amino acids when they are broken down?

A

By transamination or deamination.

68
Q

What is transamination?

A

A mechanism for removal of -NH2 from amino acids. Aminotransferases swap R groups of amino acids. Most aminotransferases use alpha ketoglurate to funnel the amino group to form glutamate.

69
Q

What molecules does aspartate aminotransferases use to transfer amino groups to ?

A

Oxaloacetate is used to gain the amino group to form aspartate.

70
Q

What coenzyme do all aminotransferases require?

A

Pyridoxal phosphate (derivate of vitamin B6)

71
Q

What hormone stimulate aminotransferase synthesis in the liver?

A

Cortisol

72
Q

Why are some aminotransferases measured in serum?

A

Alanine aminotransferases and aspartate aminotransferase are both measured in serum to asses liver function levels. Conditions that cause cellular necrosis ( viral hepatitis, autoimmune liver diseases and toxic injury) raise levels of aspartate aminotransferase and alanine aminotransferase.

73
Q

What is deamination?

A

A mechanism of liberating the amino group from amino acids as free ammonia. D amino acid oxidases are low specifity enzymes that convert amino acids into keto acids and ammonia.

74
Q

Where does deamination occur?

A

In the liver and kidneys

75
Q

What is glutaminase?

A

A high specificity enzyme involved in the deamination of glutamine to glutamate. Involved in non-essential amino acid synthesis. Glutamate is a keto acid that can be utilised for energy.

76
Q

Why is ammonia converted to urea?

A

Ammonia is toxic whilst urea is not. Urea is also water soluble so can be easily excreted in urine. Urea is chemically inert.

77
Q

What are the products of amino acid catabolism used for?

A

The amino group can be used for synthesis of non-essential amino acids as well as other N-continuing compounds or ammonia/urea.
The carbon skeleton can be utilised for energy in oxidative metabolism

78
Q

What is the function of alanine aminotransferase?

A

Converts alanine to glutamate

79
Q

What is the function of aspartate aminotransferase

?

A

Converts glutamate to aspartate

80
Q

What are death cap mushrooms?

A

Mushrooms that cause acute liver failure if ingested. Raise plasma alanine aminotransferase levels up to 20 times normal levels.

81
Q

How is the concentration of dietary ammonia kept low?

A

Rapidly converted to ammonium ion NH4. Ammonia and ammonia ions are absorbed in the gut so concentration in peripheral blood is kept low.

82
Q

Where does the urea cycle occur?

A

In the liver

83
Q

How many enzymes are involved in the urea cycle?

A

5

84
Q

How are enzymes in the urea cycle controlled?

A

Enzymes are induced by high protein diet and suppressed by low protein diet or starvation. Cannot be regulated by feedback inhibition as the final product urea is disposed of in urine.

85
Q

What is refeeding syndrome?

A

Can occur when nutritional support given
to severely malnourished patients.

  • Starving individuals have very low activity of the enzymes of the urea cycle
  • rapid refeeding leads to ammonia toxicity (hyperammonaemia as the excess amino acids are degraded).
  • More significantly, the rapid re-feeding of energy rich foods in starved or inadequately nourished patients will rapidly increase blood sugar and insulin, resulting in glycogen, fat and protein synthesis. These processes will utilise magnesium, phosphate and potassium from body stores that are already depleted and therefore result in electrolyte abnormalities such as hypophosphataemia resulting in a condition known as refeeding syndrome.
86
Q

What patients are at risk of developing refeeding syndrome?

A 
Low BMI (<16)
Unintentional weight loss of >15% in 3-6 months
10 days or more with little to no nutritional intake
87
Q

What causes defects in the urea cycle?

A

Autosomal recessive genetic disorders caused by deficiency of one of the enzymes in the urea cycle. Mutations cause a partial loss of enzyme function

88
Q

What clinical problems may result in a patient with a defect in the urea cycle?

A

Hyperammonaemia

Accumulation/excretion of urea cycle intermediates

89
Q

What are the symptoms of a patient with a defect in their urea cycle?

A

• Vomiting • Lethargy • Irritability • Mental retardation • Seizures • Coma

90
Q

What affects the severity of the presenting symptoms of a patient with defects in their urea cycle?

A

Nature of the defect

Amount of protein eaten

91
Q

How can we manage urea cycle deficiencies?

A

Low protein diet

Replace amino acids in diet with keto acids (as keto acids are converted to amino acids using some of the NH4+ ammonium ion

92
Q

What conditions may cause hyperammonaemia as a secondary consequence?

A

Defect in the urea cycle (autosomal recessive genetic disorder caused by deficiency in one of the enzyme of the urea cycle)

Liver diseases such as liver cirrhosis ( affect the livers ability to remove ammonia from the portal blood system)

93
Q

Why is ammonia toxic to the CNS?

A

Readily diffusible and easily crosses the blood brain barrier and extremely toxic to brain. Ammonia removes keto acids and removes enzymes (alpha ketoglutarate) from the TCA cycle, slowing and disrupting energy supply to brain cells. Also affects the pH inside the cells of the CNS and interfere with neurotransmitter synthesis and release.

94
Q

What are the potential toxic effects of ammonia to cells of the body?

A

Interference with amino acid transport and protein synthesis
Disruption of cerebral blood flow
pH effects (alkaline)
Interference with metabolism of excitatory amino acid
neurotransmitters (e.g. glutamate and aspartate)
Alteration of the blood–brain barrier
Interference with TCA cycle (reacts with α-ketoglutarate to
form glutamate)

95
Q

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

A
  1. Glutamine - ammonia is combined with glutamate to form glutamine which can be transported in the blood. Glutamine synthetase stimulates this reaction. Opposite to the glutaminase.
  2. Alanine
    Amine groups transferred to glutamate by transamination of amino acid and alpha ketoglutarate. Pyruvate then transaminated by glutamate to form alanine. Alanine transported in blood to liver.
96
Q

Glutamine and alanine carry amino groups to the liver. What happens when they enter the liver?

A
  1. Glutamine transported in blood to liver or
    kidneys where it is cleaved by glutaminase to
    reform glutamate and ammonia. In liver ammonia fed into urea cycle. In kidney excreted directly in urine
  2. Alanine transported in blood to liver where it is converted back to pyruvate by transamination. Amino group fed via glutamate into urea cycle for disposal as urea whereas pyruvate is used to synthesise glucose which can be fed back to tissues
97
Q

If left untreated, what impairment occurs in patients with problems with amino acid metabolism?

A

Intellectual impairment.

98
Q

How do we scan for protein metabolism enzyme deficiency?

A

Heel prick test on new borns.

99
Q

Give some examples of inborn errors of protein metabolism

A 
Phenylketonuria (PKU)
Maple syrup urine disease
Isovaleric acidaemia (IVA)
Glutaric aciduria
Homocystinuria
100
Q

What is phenylketonuria?

A

Most common inborn error of amino acid

metabolism. Deficiency in phenylalanine hydroxylase. Autosomal recessive. Affected gene is on chromosome 12

101
Q

What occurs in patients with phenylketonuria?

A

Accumulation of
phenylalanine in tissue,
plasma & urine. Phenylketones made from phenylalanine are present in urine, giving urine a musty smell.

102
Q

How is phenylketonuria treated?

A

Strictly controlled low
phenylalanine diet
enriched with tyrosine. Avoid artificial sweeteners
(contain phenylalanine). Avoid high protein foods such
as meat, milk, and eggs.

103
Q

Why are patients with phenylketonuria deficient in tyrosine?

A

Defect in phenylalanine hydroxylase which functions by catalysing phenylalanine to from tyrosine. As phenylalanine hydroxylase is deficient, tyrosine cannot be synthesised in this way.

104
Q

What pathways are affected by a deficiency in tyrosine?

A 
Noradrenaline
Adrenaline 
Dopamine
Melanin 
Thyroid hormone
Protein synthesis
105
Q

What are symptoms of phenylketonuria?

A

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

Can be avoided with early intervention

106
Q

How does PKU affect brain development?

A

Deficiency in phenylalanine hydroxylase results in high levels of phenylalanine which is a large neutral amino acid (LNAA). This competes for transport across the blood brain barrier via Large Neutral Amino Acid Transporter. (LNAAT). Excess phenylalanine saturates the transporter and levels of other LNAA in the brain decreases. Protein and neurotransmitter synthesis is reduced and Brian development is affected.

107
Q

What is homocystinuria?

A

Problem breaking down methionine. Excess homocystine (oxidised form of homocysteine) excreted in urine. Autosomal recessive disorders. Incidence ~1 in 344,000. Defect in cystathionine β-synthase most common. Affects connective tissue, muscles, CNS, CVS

108
Q

What is a treatment of homocystinuria?

A 
Low-methionine diet 
Avoid milk, meat, fish, cheese, eggs 
Nuts, and peanut butter also
contain methionine 
Cysteine, Vit B6, Betaine, B12 &amp; Folate supplement
109
Q

Why is homocystinuria often misdiagnosed?

A

In children, the symptoms of homocystinuria are very similar to the symptoms form marfans syndrome and children can easily be misdiagnosed. In homocystinuria protein structure is disrupted. Both have similar clinical features such as skeletal deformities and lens dislocation.

110
Q

In homocystinuria build up of what molecules cause disease symptoms?

A

Homocysteine and methionine

111
Q

How is homocystinuria detected?

A

Elevated homocysteine and methionine in plasm and the presence homocystine in urine.

112
Q

How are the clinical problems of homocystinuria?

A

Elevated plasma Cystathionine
homocysteine shown to be associated with cardiovascular disease
Disorders of connective tissues, muscle and CVS. Excess homocysteine causes damage to collagen and elastic fibres in connective tissue. Metabolites of methionine are toxic to neurones and cause neurological dysfunction.

MEH (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions