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ESA1 - Metabolism > Protein & Amino Acid Metabolism > Flashcards

Protein & Amino Acid Metabolism Flashcards

1
Q

How is Creatinine formed?

A
  • Breakdown product of CREATINE and CREATINE PHOSPHATE in muscle
  • Produced at a constant rate depending on muscle mass (unless muscle is wasting)
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2
Q

Explain how creatinine is used as a clinical marker

A
  • Provides an estimate of muscle mass (creatinine measured over 24hrs in urine -> proportional to muscle mass)
  • Used as an indicator of renal function as it provides an estimate for glomerular filtrate rate (raised levels indicate damage to nephrons)
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3
Q

Define protein turnover

A

Balance between protein synthesis and protein degradation (proteolysis)

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4
Q

List 5 Nitrogen containing compounds found in the body

A
  • Amino acids
  • Proteins
  • Purines and pyrimidines (DNA/RNA)
  • Neurotransmitters e.g. Dopamine
  • Some hormones e.g. Adrenaline
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5
Q

Define nitrogen balance

A

The balance between the nitrogen taken into our bodies through diet and the nitrogen lost or excreted from body

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7
Q

Explain the importance of nitrogen balance in the body

A
  • Positive N balance: INTAKE > OUTPUT so there is an increase in total body protein
  • Negative N balance: INTAKE
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8
Q

What is the difference between GLUCOGENIC and KETOGENIC amino acids?

A
  • GLUCOGENIC amino acids can be converted into glucose via gluconeogenesis
  • KETOGENIC amino acids can be degraded into Acetyl CoA, which is the precursor of ketone bodies
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9
Q

List the amino acids which are GLUCOGENIC

A
  • Alanine
  • Cysteine
  • Aspartic acid
  • Asparagine
  • Arginine
  • Histidine
  • Proline
  • Glutamine
  • Methionine
  • Valine
  • Glycine
  • Serine
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10
Q

List the amino acids which are KETOGENIC

A
  • Lysine

- Leucine

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11
Q

List the amino acids which can be either GLUCOGENIC or KETOGENIC

A
  • Tryptophan
  • Threonine
  • Tyrosine
  • Phenylalanine
  • Isoleucine
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12
Q

What are the 9 essential amino acids that cannot be synthesised by the body?

A
  • Isoleucine
  • Lysine
  • Threonine
  • Histidine
  • Leucine
  • Methionine
  • Phenylalanine
  • Tryptophan
  • Valine
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13
Q

What is the name of the process by which amino acids can be converted to glucose?

A

GLUCONEOGENESIS

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14
Q

What is the effect of insulin on protein turnover?

A
  • INCREASES protein synthesis

- DECREASES protein degradation

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15
Q

Explain the role of TYROSINE in the synthesis of important N-containing compounds

A
  • Production of thyroid hormones (T3 and T4 synthesised from Tyrosine residues)
  • Production of menalin (skin)
  • Production of NEUROTRANSMITTERS e.g. noradrenaline
  • Absence of Tyrosine can lead to mental retardation
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16
Q

State the use of nitric oxide in the body and the amino acid derivative

A
  • Derived from ARGININE
  • Role in vasodilation
  • Gaseous signalling molecule
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17
Q

What is HISTAMINE?

A
  • Nitrogenous compound produced from HISTIDINE

- Secreted by mast cells/basophils during immune/hypersensitivity response

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18
Q

What is TRANSAMINATION?

A

The transfer of an amino group from one amino acid to a keto acid, forming an amino acid which can enter the urea cycle and undergo DEAMINATION

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19
Q

What is DEAMINATION?

A

The removal of an amino group from an amino acid, producing AMMONIA and a keto acid

20
Q

Where does DEAMINATION occur?

A

LIVER and KIDNEY

21
Q

How can the body synthesise amino acids?

A

Use of carbon atoms from:

  • Intermediates of glycolysis (C3)
  • Pentose phosphate pathway (C4, C5)
  • Krebs cycle (C4, C5)

Amine group provided through TRANSAMINATION or from ammonia

22
Q

Why is the removal of nitrogen from amino acids essential?

A
  • Carbon skeleton can be utilised in oxidative metabolism

- Once removed N can be incorporated into other compounds or excreted as UREA

23
Q

Describe the formation of GLUTAMATE through transamination of ALANINE

A
  • Alanine + a-ketoglutarate —-> Glutamate + pyruvate

- Catalysed by the enzyme ALANINE AMINOTRANSFERASE (ALT)

24
Q

Explain the role of ASPARTATE AMINOTRANSFERASE (AST) in transamination

A
  • Conversion of Glutamate to Aspartate
  • Glutamate + α-ketoglutarate —-> Aspartate + oxaloacetate
  • Aspartate can undergo DEAMINATION and enter Urea Cycle
25
Q

Why must ammonia be converted to urea?

A
  • Ammonia is highly toxic

- Urea is non-toxic and chemically inert and can be excreted from body in the urine

26
Q

Describe the potential toxic effects of ammonia

A
  • Increase in blood pH (alkaline)
  • Interference with amino acid transport and protein synthesis
  • Alteration of blood-brain barrier
  • Interference with Krebs cycle (reacts with a-ketoglutarate to form Glu)
27
Q

How is ammonia transported in the blood?

A
  • Combines with Glutamate to form GLUTAMINE, which is transported in blood to the liver where it is converted back to Glu and NH3
  • Combines with pyruvate to form Alanine which is transported to liver and used to synthesise Glutamate through transamination
28
Q

State the significance of the heel prick test in newborns

A
  • Systematically screen for inborn errors in amino acid metabolism
  • Diseases can be identified early so treatment methods can be put in place to avoid permanent damage
  • These may include modifications to the diet
29
Q

Explain how Phenylketonuria (PKU) can lead to the presence of phenylketones in the urine

A
  • Deficiency in PHENYLALANINE HYDROXYLASE
  • Accumulation of Phenylalanine which undergoes transamination to form PHENYLPYRUVATE
  • Phenylpyruvate can form phenylketones such as phenyllactate and phenylacetate which are present in the urine
30
Q

Why might PKU lead to mental retardation?

A
  • Deficiency in Phenylalanine Hydroxylase enzyme means that phenylalanine cannot be converted to TYROSINE
  • Tyrosine is important in the the production of various neurotransmitters - other pathways affected
31
Q

What are the treatment methods for PKU?

A
  • Low Phenylalanine in diet
  • Avoid high protein foods e.g. meat, fish, eggs
  • Avoid artificial sweeteners (may contain Phe)
32
Q

What causes Homocystinuria?

A
  • AUTOSOMAL RECESSIVE DISORDER
  • Deficiency of CYSTATHIONINE B-SYNTHASE enzyme means that Methionine cannot be broken down
  • Accumulation of HOMOCYSTEINE and methionine - HOMOCYSTINE present in urine
  • High levels of homocysteine and methionine are associated with CVD
33
Q

What are the treatment methods for Homocystinuria?

A
  • Low methionine diet
  • Avoid meat, fish, eggs, nuts and nut butters
  • Supplement diet with Cysteine, Vitamins B12 and B6, Betaine and Folate
34
Q

How could you clinically test for high levels of ALT and AST and what could this indicate?

A
  • Plasma levels of ALT and AST are measured routinely as part of a liver function test (blood test)
  • High levels indicate extensive cellular necrosis (conditions such as viral hepatitis, autoimmune liver disease and toxic injury)
35
Q

Which 2 amino acids can undergo deamination?

A
  • GLUTAMATE

- ASPARTATE

36
Q

What causes Phenylketonuria (PKU)?

A
  • Autosomal recessive disorder due to mutation of gene coding for PHENYLALANINE HYDROXYLASE
  • Gene located on chromosome 12
37
Q

What diseases can occur due to lack of protein in diet?

A
  • Kwashiorkor (protein deficient)

- Marasmus (energy deficient)

38
Q

Explain how lack of protein can cause oedema

A
  • Decrease in oncotic pressure due to lack of protein in blood
  • Hydrostatic pressure > oncotic pressure which leads to net flow of fluid out of capillaries and into tissues
  • This can cause swelling of tissues (oedema)
39
Q

Give 3 examples of high N-containing compounds in the body

A
  • Proteins
  • DNA
  • RNA
40
Q

Give 3 examples of low N-containing compounds in the body

A
  • Amino acids
  • Purines/pyrimidines
  • Neurotransmitters
41
Q

How does Nitrogen enter and leave the body?

A
  • Most N enters as proteins
  • Most N leaves body through excretion of urine (urea, creatinine, ammonia and uric acid)
  • Some N lost directly (skin, hair nails etc.)
42
Q

When might the body show a positive N balance?

A

During:

  • Growth
  • Pregnancy
  • Convalescence
  • Tissue repair
43
Q

Explain why tyrosine, cysteine and arginine are not classed as ‘essential amino acids’

A
  • Can be synthesised by the body
  • Tyrosine can be synthesised from Phenylalanine
  • Cysteine can be synthesised from Methionine
  • Arginine can be synthesised from Citrulline
44
Q

How can cells attempt to reduce the toxicity of ammonia?

A
  • Synthesis of GLUTAMINE from NH3 and glutamate using GLUTAMINE SYNTHETASE
  • Glutamine is transported to liver and kidney where it is converted back to glutamate and NH3 using GLUTAMINASE
  • NH3 can be converted to urea in liver or directly excreted in urine in kidneys

ESA1 - Metabolism (20 decks)

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