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Z OLD ESA 1- Metabolism > Protein and Amino Acid Metabolism > Flashcards

Protein and Amino Acid Metabolism Flashcards

1
Q

Give 8 nitrogen containing compounds in the body?

A

Amino acids, Proteins, Purines, Pyrimidines, Porphyrins (haem), Creatine, Neurotransmitters (e.g. dopamines, Some hormones (e.g. adrenaline)

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2
Q

What is creatinine?

A

Breakdown product of creatine and creatine phosphate

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3
Q

What can creatinine be used as?

A

A useful clinical marker

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4
Q

Where is creatinine produced?

A

In muscle

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5
Q

What can creatine phosphate be used as?

A

A very short term energy supply of ATP in skeletal muscle

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6
Q

At what rate is creatinine usually produced?

A

Constant rate depending on muscle mass

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7
Q

How is creatinine excreted?

A

Filtered via kidneys into urine

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8
Q

What is creatinine excretion over a 24 hour period proportional to?

A

Muscle mass

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9
Q

What is the result of creatinine excretion over 24hrs being proportional to muscle mass?

A

It can provide an estimate for muscle mass

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10
Q

What is creatinine commonly used as an indicator for?

A

Renal function

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11
Q

What do raised creatinine levels indicate regarding kidney function?

A

Damaged nephrons

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12
Q

Why can’t we use a urine volume to determine nephron damage?

A

Because would vary depending on urine dilution

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13
Q

When is the body said to be in N equilibrium?

A

When intake = output

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14
Q

What is happening to body protein in N equilibrium?

A

No change in total body protein

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15
Q

When is N equilibrium normal?

A

In adults

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16
Q

What is happening in positive N balance?

A

Intake > output

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17
Q

What happens to body protein in positive N balance?

A

Increase in total body protein

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18
Q

When is positive N balance the normal state?

A

In pregnancy, growth or an adult recovering from malnutrition

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19
Q

What is negative N balance?

A

When intake

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20
Q

What happens to body protein in negative N balance?

A

Net loss of body protein

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21
Q

When is negative N balance normal?

A

Never

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22
Q

Give 3 causes of negative N balance

A

NAME?

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23
Q

Describe the nitrogen balance in a 70kg male

A
  • 16g N in from dietary nitrogen
  • 16g N in amino acid pool
  • 2g N lost in skin, hair and nails
  • 14g N lost in N-waste products
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24
Q

Where does the N in the amino acid pool go?

A

N-containing compounds, and cycled round to and from body protein

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25
Q

How much is there of N-containing compounds in the body of a 70kg male?

A

60g

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26
Q

How much of body protein is there in the body of a 70kg male?

A

2kg

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27
Q

What are the N-waste products?

A

NAME?

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28
Q

What is given when dietary protein is digested?

A

Free amino acids

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29
Q

Other than dietary protein digestion, how can free amino acids be produced?

A

By de novo amino acid synthesis

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30
Q

What are free amino acids in cycle with?

A

Cellular proteins in muscle

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31
Q

What happens in the cycle between free amino acids and cellular proteins in muscle?

A

Free amino acids are made into cellular proteins in synthesis, and cellular proteins are made into free amino acids in proteolysis

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32
Q

What happens to free amino acids in emergency situations?

A

They are split into their carbon skeleton and amino group in the liver

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33
Q

What happens to the amino group produced when free amino acids are split in emergency situations?

A

It is converted into urea, and excreted in urine

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34
Q

What happens to the carbon skeleton produced when free amino acids are split in emergency situations?

A
  • Glucogenic amino acids undergo gluconeogenesis

- Ketogenic amino acids are converted to ketone bodies

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35
Q

What is a glucogenic amino acid?

A

One that can be converted to glucose by gluconeogenesis

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36
Q

Give 2 glucogenic amino acids

A

NAME?

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37
Q

What is a ketogenic amino acid?

A

One that can be converted into ketone bodies

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38
Q

Give 2 ketogenic amino acids

A

NAME?

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39
Q

Give 2 amino acids that are both glucogenic and ketogenic

A

NAME?

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40
Q

What does wether an amino acid is glucogenic or ketogenic depend on?

A

The side chain

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41
Q

What can protein be mobilised to produce?

A

Glucose

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42
Q

Why is protein mobilised to produce glucose?

A

To meet the need for glucose of some tissues

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43
Q

When does mobilisation of protein reserves occur?

A

During extreme stress, including starvation

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44
Q

How is mobilisation of protein reserves controlled?

A

Hormones

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45
Q

Which hormones control the mobilisation of protein reserves?

A
  • Insulin
  • Growth hormone
  • Glucocorticoids (e.g. cortisol)
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46
Q

What is the effect of insulin and growth hormone on protein?

A

NAME?

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47
Q

What effect do glucocorticoids have on protein?

A
  • Decrease protein synthesis

- Increase protein degradation

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48
Q

When can excessive breakdown of protein occur?

A

Cushing’s syndrome

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49
Q

What is Cushing’s syndrome caused by?

A

Excess cortisol

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50
Q

What is the result of the excessive breakdown of protein in Cushing’s syndrome?

A

It weakens the skin structure, leading to striae formation

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51
Q

How many different types of R groups are there in amino acids?

A

20

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52
Q

What does an amino acids R group determine?

A

What type of amino acid it is

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53
Q

How do amino acids link together?

A

Through the formation of peptide bonds

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54
Q

How can amino acids be obtained other than dietary intake?

A

The body can synthesise some amino acids that it requires

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55
Q

Where do the carbon atoms for non-essential amino acids come from?

A
  • Intermediates of glycolysis (C3)
  • Pentose phosphate pathway (C4 & C5)
  • Krebs cycle (C4 & C5)
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56
Q

Where does the amino group for non-essential amino acids come from?

A

NAME?

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57
Q

What are amino acids required for?

A

Synthesis of other important compounds

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58
Q

Give 3 things tyrosine is important for the synthesis of

A
  • Catecholamines
  • Melanin
  • Thyroid hormones
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59
Q

What is histidine important for the synthesis of?

A

Histamine

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60
Q

What is arginine important in the synthesis of?

A

Nitric oxide

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61
Q

What is nitric oxide important for?

A

Vasaldilation

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62
Q

Give 2 things cysteine is important for the synthesis of?

A
  • Hydrogen sulphide

- Glutathione

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63
Q

What is hydrogen sulphide important for?

A

Signalling

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64
Q

What is serine important in the synthesis of?

A

Sphingosine

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65
Q

Give 3 things tryptophan is important in the synthesis of?

A

NAME?

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66
Q

Give 4 things glycine is important in the synthesis of

A
  • Purines
  • Glutathione
  • Haem
  • Creatine
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67
Q

Why is the ability to remove nitrogen from amino acids essential?

A

To allow the carbon skeleton of amino acids to be utilised in oxidative metabolism

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68
Q

What can happen to nitrogen from amino acids once removed?

A

It can be incorporated into other components or excreted from the body as urea

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69
Q

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

A

NAME?

70
Q

What enzyme is required for transamination?

A

Aminotransferase

71
Q

What does aminotransferase do?

A

Transfers the amino group from amino acid to the keto acid α-ketoglutarate

72
Q

What is the result of the action of aminotransferase?

A

The amino acid is converted to a keto acid, and the keto acid α-ketoglutarate is converted to glutamate

73
Q

What is the alternative to using the keto acid α-ketogluatarate for transamination?

A

Using the keto acid oxaloacetate

74
Q

What enzyme is required when using the keto acid oxaloacetate for transamination?

A

Aspartate aminotransferase

75
Q

What does aspartate aminotransferase do?

A

Converts the amino acid to a keto acid, and oxaloacetate to aspartate

76
Q

What do all amino transferases require?

A

The coenzyme pyridoxal phosphate

77
Q

What is pyridoxal phosphate a derivative of?

A

Vitamin B

78
Q

What are the key aminotransferase enzymes?

A
  • Alanine aminotransferase (ALT)

- Aspartate aminotransferase (AST)

79
Q

What amino acid conversion does alanine aminotransferase catalyse?

A

Alanine to glutamate

80
Q

What amino acid conversion does aspartate aminotransferase catalyse?

A

Glutamate to aspartate

81
Q

What is routinely measured as part of a liver function test?

A

Plasma ALT and AST levels

82
Q

What do the results of the plasma ALT and AST levels mean?

A

Aren’t normally present in plasma, so if found, bad

83
Q

Where will plasma ALT and AST increase?

A

In conditions causing extensive cellular necrosis

84
Q

Give 3 conditions that may cause extreme cellular necrosis

A
  • Viral hepatitis
  • Autoimmune liver disease
  • Toxic injury
85
Q

What does deamination do?

A

Liberates amin group as free ammonia

86
Q

Where does deamination mainly occur?

A

In the liver and kidney

87
Q

What is deamination important for?

A
  • Utilisation of keto acids for energy

- Deamination of dietary D-amino acids

88
Q

Where are dietary D-amino acids found?

A

NAME?

89
Q

What is the problem with ammonia?

A

It’s very toxic

90
Q

What must be done to ammonia in the body?

A

Must be removed

91
Q

How is ammonia removed?

A

NAME?

92
Q

What happens to ammonia at physiological pH?

A

It is rapidly converted to ammonium ion

93
Q

Give 3 enzymes that can deaminate amino acids

A
  • Amino acid oxidases
  • Glutaminase
  • Glutamate dehydrogenase
94
Q

Does urea have a high or low nitrogen content?

A

High

95
Q

Is urea toxic?

A

No

96
Q

Is urea hydrophilic or hydrophobic?

A

Very hydrophilic

97
Q

What is the advantage of urea being very hydrophilic?

A

It is very water soluble, so can easily excrete in urine

98
Q

Is urea chemically reactive or inert?

A

Inert

99
Q

How can urea be broken down?

A

By bacteria

100
Q

What is released when bacteria break down urea?

A

NH 3

101
Q

How is most urea excreted?

A

In urine via kidneys

102
Q

What important role does urea perform in kidney tubules?

A

Osmotic role

103
Q

Where does the urea cycle occur?

A

In the liver

104
Q

How many enzymes does the urea cycle involve?

A

5

105
Q

What is the amount of urea normally related to?

A

Need to dispose of urea

106
Q

Is amount of urea under direct control?

A

No, just governed by amount of substrate

107
Q

What induces high urea cycle enzyme levels?

A

A high protein diet

108
Q

What represses urea cycle protein levels?

A
  • Low protein diet

- Starvation

109
Q

Is the urea cycle regulated?

A

No, but can be induced

110
Q

When can re-feeding syndrome occur?

A

When nutritional support is given to severely malnourished patients

111
Q

What causes re-feeding syndrome?

A

Ammonia toxicity

112
Q

Why does ammonia toxicity occur when re-feeding malnourished patients?

A

Because the urea cycle has been down regulated, so the body can’t cope with the amount of ammonia being produced

113
Q

How is re-feeding syndrome prevented?

A

By re-feeding at 5 to 10 kcal per kg per day, raising gradually to full needs within a week

114
Q

What are the risk factors for re-feeding syndrome?

A
  • BMI 15% in 3-6 months

- ~17 days with little/no nutritional intake

115
Q

What causes defects in the urea cycle?

A

Autosomal recessive genetic disorders

116
Q

What defects occur in the urea cycle?

A

Deficiency in one of the enzymes in the urea cycle

117
Q

How often to defects in the urea cycle occur?

A

~1 in 30,000 live births

118
Q

What do mutations in enzymes involved in the urea cycle cause?

A

Partial loss of enzyme function

119
Q

Why are defects in the urea cycle only partial losses of enzyme function?

A

Complete loss would be incompatible with life, and the foetus would die

120
Q

What do defects in the urea cycle lead to?

A
  • Hyperammonemia

- Accumulation/excretion of urea cycle intermediates

121
Q

What is hyperammonemia?

A

Too much ammonia in the blood

122
Q

What does the severity of defects in the urea cycle depend on?

A
  • Nature of defect

- Amount of protein eaten

123
Q

How quickly do severe urea cycle disorders show symptoms?

A

Within 1 day of birth

124
Q

What happens if severe urea cycle defects are left untreated?

A

The patient will die

125
Q

What can be the case with mild urea cycle deficiencies?

A

Symptoms don’t show until early childhood

126
Q

What are the symptoms of urea cycle deficiencies

A
  • Vomiting
  • Lethargy
  • Irritability
  • Mental retardation
  • Seizures
  • Coma
127
Q

How are urea cycle disorders managed?

A
  • Low protein diet

- Replace amino acids in diet with keto acids

128
Q

What is the biochemical basic of ammonia toxicity?

A

It is readily diffusible, so can easily access through the blood brain barrier, and is highly toxic to the brain

129
Q

At what levels must blood levels of ammonia be kept?

A

Very low- 25-50µmol/L

130
Q

What are the potential effects of too much ammonia?

A
  • Interfere with amino acid transport and protein synthesis
  • Disruption of cerebral blood flow
  • Alkalisation of blood
  • Interfere with metabolism of excitatory amino acid neurotransmitters
  • Alteration of blood-brain barrier
  • Interfere with TCA cycle
131
Q

Why can excess ammonia interfere with the TCA cycle?

A

It can react with α-ketoglutarate to form glutamate

132
Q

What are the two mechanisms for the safe transport of ammonia from tissues for disposal?

A
  • Glutamine

- Alanine

133
Q

How does the glutamine mechanism of safe ammonia transport work?

A
  • Ammonia combined with glutamate to form glutamine
  • Glutamine transported in blood to liver or kidneys, where it is cleaved by glutaminase to reform glutamate and ammonia
  • In the liver, ammonia is fed into the urea cycle.
  • In the kidney, ammonia is excreted directly into urine
134
Q

How does the alanine mechanism of safe ammonia transport work?

A
  • Alanine formed in peripheral tissues by transamination of pyruvate- essentially, pyruvate is combined with ammonia to form alanine
  • Alanine is transported in blood to the liver
  • In the liver, it is converted back to pyruvate by transamination
  • Amino group is fed via glutamate into urea cycle for disposal as urea, and pyruvate is used to synthesise glucose
135
Q

How many inherited diseases involving defects in amino acid metabolism are there?

A

Over 50

136
Q

What causes defects in amino acid metabolism?

A

Either total, or more commonly partial, loss of enzyme activity

137
Q

What can happen is problems in amino acid metabolism are left untreated?

A

They frequently lead to intellectual impairment

138
Q

What does treatment of defects in amino acid metabolism involve?

A

Restricting specific amino acids in the diet

139
Q

What is the heel prick test?

A

A test that every child in western countries receives to systematically screen for diseases

140
Q

What diseases are tested for with the heel prick test?

A
  • Sickle cell disease
  • Cystic fibrosis
  • Congenital hyperthyroidism
  • Inborn errors in metabolism
141
Q

What inborn errors in metabolism are tested for using the heel prick test?

A
  • Phenylketonuria
  • Maple syrup urine disease
  • Isovaleric acidaemia
  • Glutaric aciduria
  • Homocystinuria
142
Q

Why are the diseases in the heel prick test tested for?

A

Because something, often dietary modification, can be done about them, but if not done as soon as possible, can lead to the development of things such as mental retardation

143
Q

What is the most common inborn error of amino acid metabolism?

A

Phenylketonuria (PKU)

144
Q

What causes PKU?

A

Deficiency in phenylalanine hydroxylase

145
Q

What is the inheritance pattern of PKU?

A

Autosomal recessive

146
Q

Where is the affected gene in PKU?

A

Chromosome 12

147
Q

What is the result of the lack of phenylalanine hydroxylase?

A

Accumulation of phenylalanine in tissue, plasma and urine

148
Q

How can PKU be detected?

A

Phenyl ketones in urine and musty smell

149
Q

What is the treatment for PKU?

A

NAME?

150
Q

What high protein foods should be avoided in PKU

A
  • Meat
  • Milk
  • Eggs
151
Q

What are the symptoms of PKU?

A
  • Severe intellectual disability
  • Developmental delay
  • Microcephaly (small head)
  • Seizures
  • Hypo-pigmentation
152
Q

How can the symptoms of PKU be avoided?

A

Early intervention

153
Q

What causes the symptoms of PKU?

A

Not producing enough tyrosine

154
Q

Why is not enough tyrosine produced in PKU?

A

No phenylalanine hydroxylase, so phenylalanine not converted to tyrosine

155
Q

What pathways are affected by lack of tyrosine?

A

NAME?

156
Q

What builds up in the blood in PKU?

A

Phenylalanine

157
Q

Where does the phenylalanine come from?

A

Dietary protein and endogenous protein

158
Q

What does the build up of phenylalanine in the blood lead to?

A

Accumulation of phenylketones

159
Q

Why does build up of phenylalanine in the blood lead to accumulation of phenylketones?

A

Because phenylalanine is converted to phenylpyruvate by transamination, which is then converted into phenylacetate and phenyllactate

160
Q

What causes homocystinurias?

A

Problems breaking down methionine

161
Q

What is the result of problems breaking down methionine?

A

Excess homocystine excreted in urine

162
Q

What is homocystine?

A

2 homocysteines linked together by a disulphide bond- the oxidised fomr of homocysteine

163
Q

What is the inheritance pattern of homocystinurias?

A

Autosomal recessive

164
Q

What defect causes homocystinurias?

A

In cystathionine

165
Q

What cystathionine defect is most common?

A

ß-synthase

166
Q

What do homocystinurias affect?

A

NAME?

167
Q

What is the treatment for homocystinurias?

A
  • Low methionine diet
  • Avoid meat, milk, fish, cheese, nuts and eggs
  • Cysteine, Vit B 6 , betaine, B 12 , and folate supplements
168
Q

What accumulates in homocystinurias?

A

Methionine and homocysteine

169
Q

Why does methionine and homocysteine accumulate in homocystinurias?

A

No cystathionine ß-synthase, so homocysteine not converted to cystathionine. Because homocysteine not removed, methionine also accumulates because they interconvert into each other

170
Q

What is the result of the lack of conversion into cystathionine in homocystinurias?

A

There is a consequent lack of cysteine, which comes from cystathionine

171
Q

What is the homocysteine to methionine conversion promoted by?

A
  • Betaine
  • B 12
  • Folate
172
Q

What is elevated plasma homocysteine shown to be associated with?

A

Increased risk of cardiovascular disease

Z OLD ESA 1- Metabolism (17 decks)

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