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Biochemistry > Amino Acid Metabolism > Flashcards

Amino Acid Metabolism Flashcards

1
Q

Name the essential amino acids

A

Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine (only kids), Leucine, Lysine (PriVaTe TIM HALL)

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2
Q

What do most transaminases require?

A

alpha ketoglutarate and glutamate

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3
Q

What does the direction of the reaction depend on?

A

The concentrations of the reactants because Keq~1

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4
Q

Transaminases require what as a prosthetic group

A

pyridoxal phosphate derived from vit B6

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5
Q

Which amino acids are not substrates for reversible transamination?

A

Lysine and Threonine

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6
Q

Is there a storage form of amino acids?

A

No

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7
Q

Amino acid metabolism heavily dependent on coenzymes derived from what?

A

vit B6, folic acid, B12, biotin, and niacin

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8
Q

What are Glycogenic Amino Acids?

A

amino acids whose carbon skeletons can be converted to glucose

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9
Q

What are ketogenic amino acids?

A

carbon skeletons can not be converted into glucose, but can be converted into ketone bodies (acetoacetate or acetoacetyl CoA) or acetyl CoA

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10
Q

What is the most important glycogenic amino acid?

A

Alanine

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11
Q

What are the reactions of alanine?

A 
Transamination with pyruvate (other than in protein synthesis)
Alanine Transaminase (ALT)
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12
Q

What are the reactions of Aspartate?

A 
Transamination with oxaloacetate
Aspartate Transaminase (AST)
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13
Q

Where does oxaloacetate come from?

A

intermediate from the TCA cycle

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14
Q

What are the reactions of Asparagine?

A

Synthesized from aspartate using glutamine as the amine donor (Asparagine synthase)
Catabolized to aspartate by asparaginase

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15
Q

What are the branched chain amino acids?

A

Valine, Leucine, and Isoleucine

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16
Q

What are the two common steps of branched chain amino acids?

A

Step 1: branched chain amino acid transaminase,
products=branched chain alphaketo acids
Step 2: branched chain alpha keto dehydrogenase
–>intramitochondrial enzyme

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17
Q

What does branched chain alpha keto dehydrogenase require? What are they derived from?

A

TPP, Lipoic acid, FAD, NAD, and CoASH

Thiamine, lipoid acid, riboflavin, niacin, and pentathenic acid respectively

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18
Q

What are the products from valine?

A

Propionyl CoA

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19
Q

What are the products from Leucine?

A

Acetoacetate and Acetyl CoA

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20
Q

What are the products of isoleucine?

A

Propionyl CoA and Acetyl CoA

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21
Q

What does Propionyl CoA carboxylase require?

A

Biotin

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22
Q

What does Methylmalonyl CoA mutase require?

A

Vit B12

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23
Q

What is Propionyl CoA metabolized to?

A

Succinyl CoA

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24
Q

What are two important enzymes required in the Propionyl CoA pathway?

A

Propionyl CoA carboxylase and Methylmalonyl CoA mutase

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25
Q

What are the hydroxy amino acids?

A

Serine and Threonine

26
Q

Describe how Serine is synthesized.

A

3-phosphoglycerate->oxidize hydroxyl group=alphaketoacid-> transaminase=serine + phosphate-> phosphatase=serine

27
Q

What is serine metabolized to?

A

3-Phosphoglycerate by transamination, reduction, and phosphorylation by glycerinate kinase

28
Q

How can Serine be converted to glycine?

A

serine hydroxymethyl transferase
requires pyridoxal phosphate
Tetrahydrofolate (THF) (metabolite of folic acid)

29
Q

Describe the two pathways that threonine is catabolized by.

A

Serine (threonine) dehydratase=alphaketobutyrate-> alpha ketoacid dehydrogenase=propionyl CoA
threonine dehydrogenase= acetyl CoA, glycine, or pyruvate

30
Q

Glycine can be synthesized from what?

A

Serine and THF (serine hydroxymethyl transferase)
Threonine (threonine dehydrogenase)
CO2, NH4, and methylene THF (glycine synthase or glycine decarboxylase) *only AA that can be formed by all its constituents

31
Q

Glycine can be catabolized by what?

A

Serine hydroxymethryl transferase = serine
glycine decarboxylase
or the reversible reaction to all constituents

32
Q

What does THF do?

A

transfers one carbon units at various oxidation states among reactions requiring them (one carbon metabolism)

33
Q

What are the uses of THF?

A

Serine, glycine, and histidine
“resynthesis” of methionine from homocysteine
synthesis of purines
formation of the methyl group of thymine

34
Q

What form of THF is most often used in other reactions?

A

N5, N10 methylene H4 Folate

35
Q

What does glutamate dehydrogenase do?

A

removes the amine as ammonium ion used for urea synthesis (liver) or excretion (kidney)
In tissues producing ammonium, it incorporates the ammonium into glutamate

Reversible reaction

36
Q

Net synthesis and catabolism of which amino acids share glutamate as an intermediate?

A

glutamine, proline, arginine, and histidine (catabolism only)

37
Q

How is glutamate associated with the TCA cycle?

A

transamination into alpha ketoglutarate

38
Q

Catabolism of arginine and proline happen through which intermediate?

A

glutamate gamma semialdehyde

39
Q

Catabolism of histidine forms what?

A

glutamate, also involves formation of N5 formimno THF

40
Q

Glutamine serves as a transport form of what?

A

ammonia
transported to other tissues requiring ammonia for the synthesis of purines, pyrimidines
also supplies the bulk of excreted ammonia from the kidneys

41
Q

Which are the sulfur amino acids?

A

methionine and cysteine

42
Q

What is the only reaction using N5 methyl THF?

A

homocysteine to methinonine requiring N5 methyl THF and vit B12

43
Q

What is methionine converted to when not being used for protein synthesis? by what?

A

S-adenosylmethionine

by methionine adenosyl transferase

44
Q

Describe how cysteine is synthesized.

A

homocysteine + serine–>alpha ketobutyrate, ammonia ion, and cysteine
cystathinine synthase or cystathionase requiring a pyradoxal phosphate

45
Q

What is cysteine synthesis dependent on?

A

availability of methionine

46
Q

What is the major route of catabolism of cysteine

A

oxidation by cysteine dioxygenase

after transamination, non enzymatic desulfurylation results in pyruvate and sulfite

47
Q

What is the major route of catabolism of cysteine

A

oxidation by cysteine dioxygenase

after transamination, non enzymatic desulfurylation results in pyruvate and sulfite

48
Q

Phenylalanine converted to tyrosine by what?

A

phenylalanine hydroxylase requiring tetrahydrobiopterin as a cofactor

49
Q

Why is tetrahydrobiopterin important?

A

No vitamin precursor

cofactor for phenylalanine hydroxylase converting phenylalanine into tyrosine

50
Q

What are phenylalanine and tyrosine catabolized to and through what?

A

fumarate and acetoacetate by tyrosine aminotransferase (TAT)

51
Q

How is TAT induced?

A

tyrosine aminotransferase

by high concentrations of tyrosine and glucocorticoid hormones

52
Q

How is TAT induced?

A

tyrosine aminotransferase

by high concentrations of tyrosine and glucocorticoid hormones

53
Q

What is the first enzyme of the tryptophan pathway and how is it induced?

A

tryptophan oxygenase

induced by high concentrations of tryptophan and glucocorticoid hormones

54
Q

What does tryptophan form during catabolism?

A

alanine
quinolinic acid (used for synthesis of NAD in the liver)
acetyl CoA

55
Q

What is the initial step in the Lysine pathway? and what does it produce?

A

removal of the epsilon amino group

producing acetoacetyl CoA

56
Q

Phenylketonuria (PKU)

A

group of disorders, deficiency of phenylalanine hydroxylase, small percentage are deficient in tetrohydrobiopterin metabolism
phenylpyruvate excreted in large quantities
toxic to CNS, IQ of 50
controlled diet low in phenylalanine
supplement tetrathydrobiopterin
female prego still need to restrict diet bc can get to fetus

57
Q

Tyrosinemia type 2 (oculocutaneous tyrosinemia)

A 
deficiency of tyrosine amino transferase
corneal opacity (tyrosine crystals in cornea), skin lesions, variable mental retardation
control diet low in tyrosine and phenylalanine
58
Q

Neonatal tyrosinemia

A

maturitional delay in activity of p-hydroxyphenylpyruvate oxidase
usually benign and resolves in one month

59
Q

Alcaptonuria

A

deficiency of homogentisate oxidase
homogentisate excreted in urine, exposed to O2 turns black
benign, greater probability of arthritis later in life

60
Q

Tyrosinemia Type 1 (hepatorenal tyrosinemia)

A

deficiency of fumarylactoacetate hydrolase
liver failure, hepatocellular carcinoma
tubular dysfunction, renal failure
painful neurologic crises
porphyria-like sx may develop due to succinylacetone accumulate inhibiting heme synthesis
NTBC or transplant

61
Q

Maple Syrup Urine Disease (MSUD)

A

branched chain alpha ketoacid dehydrogenase deficiency
excretory products produce maple syrup odor
severe mental retardation, shortened lifespan
treatment dietary

Biochemistry (3 decks)

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