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Physiology Metabolism > Metabolism 10: Amino Acid Metabolism > Flashcards

Metabolism 10: Amino Acid Metabolism Flashcards

1
Q

What is the normal body concentrations of free amino acids?

A

<1mM plasma

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2
Q

Where do free amino acids come from?

A

degradation of ingested protein
biosynthesis of some amino acids
degradation of endogenous proteins

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3
Q

What are free amino acids used for?

A

resynthesis of endogenous protein
precursor for synthesis of other biomolecules
energy production

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4
Q

What are nutritionally essential amino acids?

A 
Amino acids that can't be synthesized in the body and thus must be obtained in the diet
ARginine
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
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5
Q

What are the 2 primary pathways for protein degradation?

A

ATP dependent ubiquitin proteosome system

Lysosomal pathway

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6
Q

What kind of proteins tend to be degraded/resynthesized faster?

A

REgulatory proteins

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7
Q

How much of the total body protein do adults degrade and resynthesize every day?

A

2-3%

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8
Q

What happens to excess amino acids?

A

They are degraded, not stored. Even on a high protein diet there is nonet accumulation of protein

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9
Q

What is the obligatory/require amino acid degradation?

A

Degradation that occurs even if no protein is supplied in diet
It is about at least 55g of protein every day. This must be replaced by dietary protein

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10
Q

What happens when daily protein intake is less than 55g?

A

Loss of body protein

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11
Q

What happens when daily protein intake is greater than 55g?

A

excess amino acids are degraded, not stored

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12
Q

During amino acid catabolism what does the nitrogen in the amino group lead to and what does the carbon skeleton lead to?

A

Nitrogen: incorporated into urea and excreted

Carbon Skeleton: converted to compounds for energy production of glycogen/fat storage

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13
Q

What is nitrogen balance?

A

Nitrogen Balance = Nitrogen Ingested (protein) - Nitrogen excreted (Urea)

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14
Q

What are some examples of physiological states in whcih we have positive nitrogen balance?

A

Growth in children
Pregnancy
bodybuilding

Protein synthesis occurs at slightly higher rate tha protein degradation -> nitrogen accumulates

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15
Q

What are some examples of physiological states in which we have negative nitrogen balance?

A

Starvation, protein malnutrition, trauma, infection, cancer, burn injury, sepsis, surgery

Rate of protein synthesis is less than rate of protein degradation -> muscle mass decreases

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16
Q

Where does urea form and where is it excreted?

A

Synthesized in the liver and excreted in the kidney

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17
Q

Show the fate of the nitrogen of the amino group of amino acids

A

NH2 from amino acids -> glutamate -> Ammonia/Aspartate -> UREA

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18
Q

What is transamination?

A

A step in the degradation of most amino acids that transfers the amino group to a-ketoglutarate to form glutamate

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19
Q

What enzyme catalyzes transamination?

A

Aminotransferase (Transaminases): different ones that act on specific amino acids. All use a-ketoglutarate as amino group acceptor to form glutamate

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20
Q

What cofactor is required for transaminases?

A

pyridoxal phosphate (Derivative of Vitamin B6)

21
Q

What are the 2 transaminases important for clinical diagnosis?

A 
Alanine Transaminase (ALT)
Aspartate Transaminase (AST)

Usually low in serum levels but increase in times of damage and cell necrosis causing release of cytosolic enzymes

22
Q

How is aspartate formed during urea biosynthesis?

A

From glutamate using aspartate transaminase to form aspartate and a-ketoglutarate

23
Q

How is ammonia formed during urea biosyntehsis?

A

From glutamate using glutamate dehydrogenase and NADP+ to form Ammonia and a-ketoglutarate and NADPH

24
Q

Show the sequence of urea synthesis from ammonia and aspartate

A

Ammonia + Aspartate -> Carboyl phosphate -> Citrulline -> Argininosuccinate -> Arginine -> urea

25
Q

What enzyme catalyzes the formation of carbamoyl phosphate?

A

Carbamoyl Phosphate Synthetase I

Requires N-acetylglutamate

26
Q

What enzyme catalyzes the formation of citrulline ?

A

Ornithine transcarbamylase

27
Q

What enzyme catalyzes the formation of argininosuccinate?

A

Argininosuccinate Synthetase

28
Q

What enzyme catalyzes the formation of arginine from argininosuccinate

A

Argininosuccinate Lyase

29
Q

What enzyme catalyzes the formation of urea and ornithine from arginine?

A

Arginase

30
Q

Which steps of urea biosynthesis occurs in the mitochondria?

A

Synthesis of carbamoyl phosphate and citrulline. All others take place in cytosol

31
Q

Which intermediate compound of urea biosynthesis leaves the mitochondria?

A

Citrulline

32
Q

Which intermediate compound of urea biosynthesis enters the mitochondria?

A

Ornithine

33
Q

How does N-acetylglutamate regulate urea biosynthesis?

A

It activates the enzyme making carbamoyl phosphate (Carbamoyl Phosphate Synthetase I) to stimulate urea production

34
Q

What causes an increase in the levels of N-acetylglutamate?

A

Increased levels of glutamate (due to transamination of amino acids from dietary protein)

35
Q

What can lead to increased levels of urea cycle enzymes?

A

Long term exposure to high protein diet or a high rate of protein degradation

36
Q

How is nitrogen from other metabolic tissue transferred to liver for conversion to urea?

A

Carried by alanine and glutamine to liver. Thus they are present in blood at higher concentrations than other amino acids

37
Q

What is BUN and its normal value?

A

Plasma urea concentration. Normal: 7-30 mg/dl

38
Q

What is the function of urea biosynthesis?

A

Detoxification of ammonia

39
Q

What can happen when ammonia levels are too high (hyperammonemia)?

A

Predisposition to coma.

Hepatic coma due to decreased ability of liver to remove ammonia via urea production

40
Q

What can cause acquired hyperammonemia?

A

Portal-Systemic Shunting: diversion of blood flow around liver in response to cirrhosis

41
Q

What can cause portal-systemic encephalopathy?

A

when ammonia produced by intestinal bacteria is absorbed but not converted to urea in the liver causing hyperammonemia

42
Q

What is a genetic cause of hyperammonemia?

A

Deficiency of a urea cycle enzyme

43
Q

What are glucogenic amino acids?

A

amino acids whose carbon skeletons are used to generate TCA intermediates or pyruvate for gluconeogenesis

44
Q

What are ketogenic amino acids?

A

amino acids whose carbon skeletons are used to generate acetyl-CoA, acetoacetyl CoA, or acetoacetate

45
Q

Which amino acids are ketogenic?

A

leucine, lysine

46
Q

Which amino acids are boht ketogenic and glucogenic?

A 
Isoleucine
Phenylalanine
Threonine
Tryptophan
Tyrosine
47
Q

What happens with regards to protein and amino acid metabolism during a fed state?

A

Get net protein synthesis using 1/3 of the newly absorbed amino acids (remaining 2/3 degraded)

48
Q

How does insulin during the fed state affect amino acid metabolism?

A

It inhibits protein degradation and stimulates protein syntehsis

49
Q

What happens with regards to protein and amino acid metabolism during a fasted state?

A

Get net protein degradation due to decreased amino acid and insulin levels. Released amino acids are used by liver for gluconeogenesis

Physiology Metabolism (11 decks)

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