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Exercise Biochemistry > Amino acid metabolism > Flashcards

Amino acid metabolism Flashcards

1
Q

When does a negative nitrogen balance occur?

A

Occurs during fasting/illness – body is breaking down proteins for energy

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2
Q

when does a positive nitrogen balance occur?

A

Occurs during growth, pregnancy

– body is building new tissue

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3
Q

How much protein is synthesized and degraded every day?

A

250g/day

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4
Q

How much protein is required per day?

A

An average adult requires ~ 0.75 g/kg/day, i.e. 75 kg man requires ~ 50g protein/day

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5
Q

How much protein is a body builder recommended?

A

1.2- 1.7 g/kg/day

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6
Q

What is the protein balance on an every day day?

A
  • 16gN in through dietary protein
  • 2kgN in the body proteins
  • 16gN in the amino acid pool
  • 60gN N-containing compounds
  • 2gN lost in skin, hair and nails
  • 14gN lost in faeces and urine
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7
Q

What are good dietary sources of protein?

A

Meat/fish – 30-35 g protein/100g

Dairy products:
cheese 20-30 g/100g
eggs 15 g/100g
milk/yoghurt 4-5 g/100g

Nuts/seeds 20-30 g/100g

Legumes (peas & beans) ~20 g/100g

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8
Q

What needs to happen for muscle growth?

A

For muscle growth protein synthesis must exceed protein breakdown
Stimulation of protein synthesis by resistance exercise – ONLY if building blocks are available

For muscles to grow you need both exercise and food
Exercise, e.g. resistance training can stimulate protein synthesis but in the absence of food catabolism will still exceed anabolism – need an intake of protein after exercise

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9
Q

When does muscle atrophy occur?

A
  • in fasting/starvation
  • in the absence of exercise
  • if there is damage to nerves supplying muscles
    e. g. after injury, someone who is confined to bed, or simply as a result of a sedentary lifestyle
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10
Q

How many essential amino acids are there in humans?

A

9

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11
Q

What are the essential amino acids?

A 
Isoleucine
Leucine
Threonine
Histidine
Lysine
Methionine
Phenylalanine
Tryptophan
Valine
(If, learned, this, huge, list, may, prove, truly, valuable
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12
Q

What conditions may require more than the 9 essential amino acids in the diet?

A
  • In pregnancy and childhood, requirement for arginine in the diet as body can’t make enough for increased growth rate.
  • Tyrosine becomes essential in PKU as the enzyme for synthesising it is missing.
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13
Q

what are the different qualities of proteins?

A

Animal protein = high quality
Plant protein= low quality as methionine and tryptophan are often lacking this means a wide variety of vegetables need to be eaten in a veggie diet

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14
Q

What do cells do with amino acids?

A
  • Protein synthesis
  • Glucose/glycogen
  • Energy (ATP)
  • Fatty acids, ketone bodies
  • Synthesis of nitrogen containing metabolites
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15
Q

what does glycine create?

A

Haem

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16
Q

what does tyrosine create?

A

dopamine, noradrenaline, adrenaline

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17
Q

what does tryptophan create?

A

serotonin

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18
Q

what does histidine create?

A

histamine

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19
Q

what does aspartate create?

A

pyrimidine bases

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20
Q

What do glycine, aspartate and glutamine create?

A

purine bases

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21
Q

What is the structure of an amino acid?

A

Amine, carboxyl and an R group

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22
Q

What happens to amino acids not required for synthetic reaction?

A

They can be used for energy, or converted to energy storage compounds
To do this, the amino group must be removed, and the nitrogen excreted

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23
Q

What is hyerammonaemia?

A

High levels of nitrogen in the blood and results in tremor, vomiting, cerebral oedema, coma and DEATH

24
Q

Where does the disposal of ammonia occur?

A

in the liver where ammonia is converted to urea for excretion by the kidneys

25
Q

What is the three step process of ammonia disposal?

A
  • transamination – transfer of amino group from amino acid to a- ketoglutarate forming glutamate (in most tissues)
  • deamination – release of ammonia from glutamate (mainly in the liver)
  • urea synthesis – urea cycle (in the liver)
26
Q

How is ammonia transported?

A

Most ammonia is transferred to either glutamate directly, or – for transport from tissues to liver as glutamine (extra ammonia group efficient transport)

27
Q

what enzyme catalyses the reaction from an amino acid (a-ketoglutarate) to a keto acid (glutamate)

A

amino transferase

28
Q

how is glutamate transferred to glutamine in the muscle?

A

addition of NH+4 and use f ATP

29
Q

how is transferred glutamine to glutamate in the liver? ?

A

removal of NH4+

30
Q

What are the two steps of ammonia disposal?

A

Step 1 transamination
: transfer of amino group from amino acids to a-ketoglutarate to form glutamate.

Step 2 deamination: release of ammonia from glutamate

31
Q

What tissues does tranamination and deamination occur in?

A

Transamination can occur in most tissues

Deamination occur mainly in the liver (also kidney)

32
Q

What is pyridoxal phosphate (B6) required for?

A
  • transamination and synthesis of non-essential amino acids
  • decarboxylation reactions required for neurotransmitter synthesis
  • haem synthesis
  • some aspects of energy metabolism & lipid synthesis
33
Q

What does a lack of pyridoxal phosphate (B6) lead too?

A
  • anaemia (lack of haem for haemoglobin)
  • neurological symptoms (lack of neurotransmitter & lipid synthesis)
  • poor growth, skin lesions, poor immune responses (lack of protein synthesis)
34
Q

Where in the cell does deamination occur?

A

Mitochondrial matrix

35
Q

What is the process of deamination?

A

Glutamate —> oxoglytarate.

This reaction takes place in the mitochondrial matrix and releases ammonia which is then combined with carbon dioxide to form carbamoyl phosphate

36
Q

Where does the urea cycle occur?

A

Mitochondrial matrix and cytosol

37
Q

What are the key enzymes in the urea cycle?

A 
1- carbomoyl-phosphate synthase 
2-Omithine carbamotltransferase 
3-Arginiosuccinate synthase 
4-Argininosuccinate lyase 
5- arginase
38
Q

What happens in the mitochondria in the urea cycle?

A

Carbamoyl phosphate formed from ammonia and bicarbonate (CO2)
– control step

Carbamoyl group transferred to ornithine to form citrulline

39
Q

What happens in the cytosol in the urea cycle?

A

Second amino group added from aspartate

Arginine formed - UREA released

40
Q

What are the steps of the urea synthesis?

A

1- (mito) carbarnoyl phosphate formed from ammonia and bicarbonate
2- Carbornyl group transferred to orithine to from atnilline
3-cytosol second amino group added form aspartate
4-arginine formed
5-Urea cleaved and released

41
Q

Where are the carbon skeletons of amino acids fed inot?

A
  • Krebs cycle
  • Fatty acid synthesis
  • Ketone sythesis
  • Glucose synthesis
42
Q

What is the difference between glucogenic and ketogenic?

A

Glucogenic: can be degraded to glucose precursors

Ketogenic: can be degraded to precursors of fatty acids and ketone bodies

Lysine and leucine can only be converted to acetyl CoA or acetoacetate – but NOT to glucose

43
Q

What are the two mechanisms for the disposal of ammonia?

A

GLUTAMINE

  • Ammonia combined with glutamate to form gluamine
  • Glutamine transported in blood to liver or kidney where it is cleaved by glutamisase to reform glumate and ammonia
  • In lover ammonia is fed into the urea cycle, in the kidney it is excreted directly into urine

ALANINE

  • Ammonia combined with pryuvate to from alanine
  • Alanine transported in blood to liver where it is converted back to pyruvate by transamination
  • Amnio grou fed via glutamate into urea cycle for disposal as urea whereas pyruvate is used in glucose synthesis
44
Q

What causes slow growth in kwashiorkor?

A

New cells require building blocks

45
Q

What causes intellectual disability in kwashiorkor?

A

you need nitrogen to make NTs.

46
Q

What causes susceptibility too infection in kwashiorkor?

A

The immune system required lots of proteins e.g. antibodies, t cells, b cells. Lots of these cells are made in early life and so if are not made they are deficient for life

47
Q

What causes skin changes in kwashiorkor?

A

Melanin is made from an amino acid and protects the skin from the sun. They have problems maintaining and manufacturing skin quaility

48
Q

What causes an enlarged liver in kwashiorkor?

A

Lots of fat in the liver as it cannot be transported out due to the lack of lipoportiens and this causes steatosis

49
Q

What causes swollen ankles in kwashiorkor?

A

Albumin in the blood reduces and therefore there is a change is osmotic pressure

50
Q

What is the net change in amino acids during moderate exercise?

A

During moderate exercise, there is a net breakdown of protein in skeletal muscle – most of the amino acids produced are released into the blood
The exception is glutamate – this is taken up during exercise. BCAA uptake and transamination is also increased during exercise.
Large amounts of glutamine and alanine are released
Some ammonia is also released by muscle during exercise

51
Q

What is the net change in amino acids during high intensity exercise?

A

During high intensity exercise glutamine and alanine release is not greatly increased. Ammonia release increases further

52
Q

With increased amino acid breakdown what happens to glutamate and glutamine synthesis?

A

Increases

53
Q

Draw the glucose alanine cycle

A

To continue transaminating amino acids, a supply of a-kg is required – since this had to come from glutamate, intake of glutamate is needed if glutamine synthesis is to continue.
The re-synthesis of a-kg requires removal of the amine group so it is transferred to pyruvate to form alanine. The alanine can leave the cell (pyruvate can’t), and travels to the liver where it can release the amino group, and is also made into glucose, which is then released into the blood and can be used by other tissues (glucose-alanine cycle)

54
Q

What happens to amino acid metabolism during moderate exercise? (link to the alanine glucose cycle)

A

Increased amino acid breakdown leads to increased glutamate and glutamine synthesis (to get rid of amino groups). Glutamine is released.
This requires a supply of α-ketoglutarate, which has to be synthesised from glutamate, also producing alanine
Extra glutamate is required to help ‘mop up’ ammonium ions, so is absorbed from blood
Alanine is released and travels to the liver, where it releases the amino group and is converted into glucose (gluconeogenesis) – glucose-alanine cycle

55
Q

Where does ammonia come from?

A

-When muscles are actively contracting, they convert large amounts of ATP
-One of the reactions that can be used to regenerate ATP is catalysed by adenylate kinase
(2ADP ADP + Pi
-This reaction is reversible, so if AMP builds up, this method for regenerating ATP will become inefficient
-So in active muscle, a further irreversible reaction is catalysed by AMP deaminase to remove AMP

AMP + H2O+ H+ —> IMP + NH4+

56
Q

What happens to amino acid metabolism in high intensity exercise?

A
  • As exercise rate increases, the need to maintain and regenerate ATP becomes top priority
  • Glutamine synthesis requires ATP and removes glutamate
  • Maintaining the levels of Krebs cycle intermediates (which can be formed from glutamate) is more important
  • Therefore glutamine and alanine release do not increase, but ammonia release does

Exercise Biochemistry (11 decks)

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