Amino Acid Metabolism Flashcards

1
Q

What is the monomer of proteins ?

A

Amino acids

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2
Q

How are amino acids generated ?

A

They are generated by the digestion of proteins in the intestine and degradation of cellular proteins

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3
Q

Can excess amino acids be stored ?

A

Excess amino acids cannot be stored

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4
Q

Describe amino acid excretion

A

They are not directly excreted, the carbon skeleton is converted to central metabolic intermediates and the amino group is excreted

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5
Q

Describe the digestion and absorption of proteins

A
  • protein digestion begins in the stomach as the acidic environment denatures proteins and pepsin degrades proteins
  • further degradation takes place in the lumen of the intestine by pancreatic proteases and peptidases e.g. trypsin and aminopeptidases
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6
Q

Describe what happens to the amino acid pool in cells

A
  • some amino acids are converted into proteins
  • some amino acids are converted into nitrogen compounds
  • surplus amino acids are split into the nitrogen amino group which is excreted and the carbon skeleton which is a fuel for energy
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7
Q

Describe events which require increased protein

A

during periods of growth :
- child
- adolescence
- pregnancy and lactation

during times of illness :
- trauma
- surgeries
- infection

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8
Q

Why are proteins needed in the oral cavity ?

A
  • collagen : basis of tooth enamel, bone, dentine and cementum
  • immunoglobulin A in saliva : resistance to infection
  • mucin : prevent the formation of caries
  • lysozymes : breakdown of food
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9
Q

What are the 2 types of amino acids ?

A
  • essential amino acids must be supplied by the diet as they cannot be synthesised in the body
  • non essential amino acids can be synthesised
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10
Q

Give some examples of essential amino acids

A
  • arginine
  • histidine
  • methionine
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11
Q

Give some examples of non essential amino acids

A
  • glutamate
  • alanine
  • asparagine
  • proline
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12
Q

How is the amino group separated from glutamate ?

A

Glutamate + water + NADP+ > 2-oxoglutarate + NADPH + NH4+

  • glutamate is oxidised and NADP+ is reduced
  • this is done by the enzyme glutamate dehydrogenase
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13
Q

How is the amino group removed from other amino acids ?

A
  • the amino group is transferred to 2-oxoglutarate by a transaminate enzyme causing it to turn into glutamate
  • the amino group is then removed from glutamate by glutamate dehydrogenase to give 2-oxoglutarate
  • the amino acid turns into a keto acid
  • there is a free NH4+ group but it is toxic
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14
Q

What happens to the free amino group ?

A
  • aquatic carnivores e.g. sharks will secrete excess nitrogen as free NH4+ because there is abundant water to disperse the NH4+ fast : ammoniotelic
  • birds and terrestrial reptiles have a limited water intake and so they want to minimise water loss and therefore secrete excess nitrogen as a paste of uric acid crystals : uricotelic
  • most terrestrial vertebrates secrete excess nitrogen as soluble urea : ureotelic
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15
Q

What is urea ?

A
  • a small molecule
  • rich in nitrogen which allows for little waste of other materials
  • non toxic so may be accumulated before excretion
  • highly soluble so can be excreted via urine
  • no ionic charge so can accumulate without ionic perturbation
  • it is produced in the urea cycle
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16
Q

Why is the urea cycle needed ?

A
  • urea is non toxic and neutral
  • access ammonium is toxic : it shifts glutamate dehydrogenase in the favour if glutamate and this lowers the production of 2-oxoglutarate and so there is less ATP produced leading to a coma
17
Q

What is the evidence for the urea cycle ?

A
  • removing the liver stopped the appearance of urea in the urine
  • a liver perfumed with nutrients produces urea
  • the liver contains a urea producing enzyme : arginase which cleaves arginine into ornithine and urea
18
Q

Where is urea synthesised ?

A

In the liver

19
Q

Describe the urea cycle

A

1) carbomoyl phosphate is produced in the mitochondrial matrix and this requires 1 ATP
2) Citrulline formation also takes place in the mitochondrial matrix
3) condensation of citrulline with aspartate takes place in the cytosol and this requires 1 ATP
4) cleavage of arginosuccinate will preserve the carbon skeleton of aspartate
5) arginine is hydrolysed to produce urea and ornithine

20
Q

Describe the nitrogen routes in the urea cycle

A

Nitrogen can enter the urea cycle via 2 routes :
1) ammonia is generated from glutamate via glutamate dehydrogenase
2) a transaminase enzyme will transfer the amino group from glutamate to oxaloacetate and this is converted to aspartate

21
Q

Describe how the urea cycle is regulated

A
  • short term regulation occurs by allosteric regulation of the first enzyme in the pathway : carbamoyl phosphate synthase and this is done by N-acetylglutamate
  • long term regulation depends on levels of synthesis of urea cycle enzymes : a high protein diet means it is unregulated and a low protein diet means it is downregulated
22
Q

How are amino acids used as an energy source in metabolism ?

A

The amino acids undergo catabolism and then act as 7 intermediates in or around the citric acid cycle

23
Q

What are ketogenic amino acids ?

A

The carbon skeleton of ketogenic amino acids are turned into ketone bodies, Acetyl CoA or fats

24
Q

What are glucogenic amino acids ?

A

The carbon skeleton is turned into glucose

25
Q

Which 2 amino acids are only ketogenic ?

A
  • Leucine
  • lysine