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Yr 2 - GI & Metabolism > Protein Metabolism > Flashcards

Protein Metabolism Flashcards

1
Q

What is the use of amino acids in the body?

A
  1. Protein synthesis
  2. Synthesis of nitrogen containing metabolites
  3. Energy (ATP)
  4. Fatty acids, ketone bodies
  5. Glucose/glycogen
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2
Q

What nitrogen containing compounds can these amino acids be turned into:

  1. Glycine
  2. Tyrosine
  3. Tryptophan
  4. Histidine
  5. Glycine/arginine
  6. Glycine, aspartate, glutamine
A
  1. Haem
  2. Dopamine, noradrenalin, adrenalin (catecholamines)
  3. Serotonin
  4. Histamine
  5. Creatine
  6. Purine bases
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3
Q

What are the signs and symptoms of malnutrition?

A
  • Poor growth
  • Susceptibility to infection
  • Changes in hair/skin colour
  • Poor skin condition and poor nutrient absorption
  • Abdominal bloating
  • Lower limb oedema
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4
Q

How does a lack of protein lead to susceptibility to infection?

A

Antibodies are proteins

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5
Q

How does a lack of protein lead to poor growth?

A

Need protein for DNA, ATP etc

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6
Q

How does a lack of protein lead to changes in hair/skin colour?

A

Insufficient melanin

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7
Q

How does a lack of protein lead to poor skin condition and poor nutrient absorption?

A

Epithelial cells have high turnover rate –> inability to replace leads to poor condition of skin

Epithelial cells also line gut, leading to problems with absorption

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8
Q

How does a lack of protein lead to lower limb oedema?

A

Lack of albumin (blood protein) –> fluid is retained and oedema occurs

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9
Q

How does a lack of protein lead to abdominal bloating?

A

Reduced albumin due to protein deficiency –> fluid accumulates in tissues, causing build up in abdomen

Accumulation of fat in liver

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10
Q

If amino acids are not required for synthetic reactions, what can they be used for? What must occur for this to happen?

A

Used for energy, or converted to energy storage compounds

Amino group must be removed and nitrogen excreted

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11
Q

Why must blood ammonia levels be kept low?

A

Ammonia is very toxic

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12
Q

What can hyperammonaemia lead to?

A

Tremor, vomiting, cerebral oedema, coma, death

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13
Q

What can hyperammonaemia be caused by?

A

Genetic defects (e.g. deficiencies of urea cycle enzymes)

More commonly caused by liver disease (hepatitis or cirrhosis)

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14
Q

How is ammonia excreted?

A

Converted to urea for excretion by the kidneys

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15
Q

What are the 3 steps in the excretion of urea?

A
  1. Transamination
  2. Deamination
  3. Urea synthesis
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16
Q

What is step 1 - transamination?

A

Transfer of amino group from amino acid to a-ketoglutarate to form glutamate (in most tissues)

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17
Q

What is step 2 - deamination?

A

Release of ammonia from glutamate (reverse)

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18
Q

Where does step 2 - deamination - mainly happen?

A

Liver

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19
Q

What is step 3 - urea synthesis?

A

Urea cycle (in liver)

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20
Q

How can ammonia be safely transported to the liver?

A

As glutamate or glutamine

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21
Q

What does step 1 (transamination) require?

A

Pyridoxal phosphate

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22
Q

What is pyridoxal phosphate?

A

The active form of vitamin B6

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23
Q

What can a lack of vitamin B6 lead to?

A
  • Anaemia (lack of haem)
  • Neurological symptoms (lack of neurotransmitter and lipid synthesis)
  • Poor growth, skin lesions, poor immune responses (lack of protein synthesis)
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24
Q

What is vitamin B6 required for?

A
  1. Transamination and synthesis of non-essential amino acids
  2. Decarboxylation reactions required for neurotransmitter synthesis
  3. Haem synthesis
  4. Some aspects of energy metabolism & lipid synthesis
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25
Q

What is the control step in urea synthesis?

A

Carbamoyl phosphate synthesis

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26
Q

What synthesises carbamoyl phosphate? What is this enzymes activated by?

A

Carbamoyl phosphate synthetase 1

Is allosterically activated by N-acetylglutamate

27
Q

When is N-acetylglutamate formed?

A

When glutamate levels are high

28
Q

What does high glutamate levels signal?

A

High levels of protein catabolism

29
Q

What is the speed of the urea cycle determined by?

A

The amount of amino acids (activated by high levels of amino acids)

30
Q

Where does the urea cycle take place?

A

Partly in the mitochondrial matrix and partly in the cytosol

31
Q

Describe the urea cycle inside the mitochondrial matrix

A
  • Carbamoyl phosphate formed from ammonia and bicarbonate – control step
  • Carbamoyl group transferred to ornithine to form citrulline
32
Q

Describe the urea cycle in the cytosol

A
  • Second amino group added from aspartate
  • Arganine formed and hydrolysed
  • Urea released
33
Q

What does uric acid contain?

A

Nitrogen

34
Q

What is uric acid derived from?

A

Purine nucleotides rather than proteins

35
Q

What is excess uric acid in the blood called?

A

Hyperuricaemia

36
Q

What can hyperuricaemia lead to?

A

Deposition of sodium urate crystals in the kidneys and in the joints

37
Q

What are deposits of sodium urate crystals in the kidneys called?

A

Kidney stones

38
Q

What are deposits of sodium urate crystals in the joints called?

A

Gout

39
Q

What is hyperuricaemia caused by?

A

Over-production of urate, or poor excretion via the kidneys

40
Q

What are high purine foods?

A

Red meat, seafood, yeast-containing foods

41
Q

What can the carbon skeleton of amino acids be fed into?

A

Several metabolic pathways:

  • Krebs cycle (used to synthesis ATP)
  • Fatty acid and ketone synthesis
  • Glucose synthesis (gluconeogenesis)
42
Q

What amino acids cannot be made into glucose? Why?

A

Lycine and Leucine

Only enter the cycle via acetyl CoA

43
Q

Describe Lycine and Leucine

A

Solely ketogenic –> can only be made into Acetyl CoA and ketone bodies

44
Q

What are glucogenic amino acids?

A

Can be degraded to glucose precursors

45
Q

What are ketogenic amino acids?

A

Can be degraded to precursors of fatty acids and ketone bodies

46
Q

Can acetyl CoA be converted to glucose?

A

No

47
Q

What is gluconeogenesis?

A

Making glucose from non-carbohydrate intermediates (during fasting or exercise)

48
Q

Where does gluconeogenesis mainly take place?

A

In the cytosol of the liver and kidney

49
Q

Gluconeogenesis takes place from what precursors?

A
  • Keto acids (derived from amino acids particularly alanine)
  • Lactate (from anaerobic glycolysis)
  • Glycerol (from triacylglycerol breakdown)
50
Q

What is gluconeogenesis vital for?

A

Maintaining blood glucose levels as glycogen stores only last about 18 hours

51
Q

Gluconeogenesis is mainly a reversal of glycolysis (but there are 3 irreversible steps in glycolysis, therefore different enzymes are required for reversal).

What 3 steps in gluconeogenesis are catalysed by different enzymes to glycolysis?

A
  1. Pyruvate –> phosphoenolpyruvate (requires several stages)
  2. Fructose 1,6 bisphosphate –> fructose 6 phosphate (fructose 1,6 bisphosphatase)
  3. Glucose 6 phosphate –> glucose (glucose 6 phosphatase)
52
Q

How is gluconeogenesis and glycolysis controlled?

A
  • High glucose and/or low energy = glycolysis

- Low glucose and/or high energy = gluconeogenesis

53
Q

What is glycolysis activated by?

A

AMP, ADP (suggests low energy)

Insulin

54
Q

What is glycolysis inhibited by?

A

ATP

Glucagon

55
Q

What is gluconeogenesis activated by?

A

Citrate
Glucagon
Acetyl CoA

56
Q

What is glyconeogenesis inhibited by?

A

AMP, ADP (suggests low energy)

Insulin

57
Q

What is not produced in type 1 diabetes?

A

Insulin

58
Q

What is effect of type 1 diabetes on glycolysis?

A

Glycolysis is inhibited (insulin is also required to allow glucose entry to muscle and adipose tissue)

Blood glucose levels rise

59
Q

Where is insulin released from?

A

Pancreas

60
Q

What is effect of type 1 diabetes on gluconeogenesis?

A

Is stimulated –> the liver synthesises and releases glucose into the circulation

Blood glucose levels rise further

61
Q

In type 1 diabetes, in order to provide substrates for gluconeogenesis, what happens?

A

Muscle protein is broken down to provide amino acids –> rapid weight loss

62
Q

Describe function of liver during exercise

A
  • Anaerobic respiration
  • Lactate production
  • Lactate removed (so glycolysis can continue)
  • Lactate travels to liver
  • Lactate converted back into glucose by gluconeogenesis which can then be released again for muscles
63
Q

Why does alcohol make you hungry?

A
  • Ethanol is metabolised in the liver
  • Produces large amounts of NADH so lowers levels of NAD+
  • NADH inhibits gluconeogenesis and lowers blood glucose (hungry)

Pyruvate and alanine is converted to lactate instead of glucose in presence of lots of NADH

Alanine –> pyruvate –> lactate

Yr 2 - GI & Metabolism (51 decks)

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