Lecture 9 - Amino Acid Catabolism 2 Flashcards

1
Q

What does high levels of glutamate cause?

A

Increased water in brain cells through osmosis, causing swelling of the brain leading to a coma

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2
Q

What is NH3 converted to and where does the conversion take place?

A
  • Urea

- Liver

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3
Q

What do organisms need to have to produce urea from arginine?

A

Arginase

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4
Q

What are the 2 compartments of the urea cycle?

A

1) Carbamoyl phosphate acts as a carrier in the mitochondrial matrix
2) NH2 enters the urea cycle in the cytosol through the conversion of ornithine to citrulline

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5
Q

What is required to make urea?

A

2 NH3; one from glutamate and one from aspartate

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6
Q

Describe the asparate-argininosuccinate shunt

A

Argininosuccinate is split into arginine (which continues the urea cycle) and fumarate (which is converted to malate and then enters TCA cycle)

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7
Q

What can deficiencies in urea cycle enzymes lead to?

A
  • Mental retardation (partial deficiency)
  • Early death (mutation in both genes)
  • NH3 build up
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8
Q

What can an NH3 buildup cause?

A
  • Activation of glutamate dehydrogenase and glutamine synthetase
  • Loss of ATP (decreases TCA cycle intermediates)
  • Increase in glutamate
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9
Q

What is the treatment for a deficiency in urea cycle enzymes?

A

Low protein diet

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10
Q

What happens to alpha-keto acids?

A

They are ultimately converted in acetyl CoA that is used in TCA cycle

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11
Q

Generally describe the threonine/glycine/serine/alanine pathway

A
  • Threonine is converted to acetyl CoA by 2 pathways
    1) Threonine -> glycine -> serine -> pyruvate -> acetyl CoA
    2) Threonine -> acetaldehyde -> acetate -> acetyl CoA
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12
Q

What can a deficiency in acetaldehyde dehydrogenase cause?

A

Alcohol intolerance

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13
Q

Which enzymes can convert alanine to pyruvate?

A

Alanine transaminase and alanine dehydrogenase

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14
Q

What is FH4?

A
  • Tetrahydrofolate

- Can transfer one carbon in many oxidation states

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15
Q

What are the 3 oxidation states of tetrahydrofolate?

A

1) N5, N10-methenyl FH4
2) N5, N10-methylene FH4
3) N5-methy FH4

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16
Q

What enzyme converts N5, N10-methenyl FH4 and N5, N10-methylene FH4 between each other and what is the cofactor?

A
  • Methenyl FH4 reductase

- NADH + H+ -> NAD+

17
Q

What enzyme converts N5, N10-methylene FH4 and N5-methy FH4 between each other and what is the cofactor?

A
  • Methylene FH4 reductase

- NADH + H+ -> NAD+

18
Q

What is the function of N5, N10-methenyl FH4?

A

Purine biosynthesis

19
Q

What can N5, N10-methylene FH4 act on?

A

Purines, pyrimidines, and amino acids

20
Q

What can N5-methy FH4 act on?

A

Amino acids

21
Q

Generally describe the phenylalanine/tyrosine pathway

A

Phenylalanine is converted to tyrosine, which is then converted to acetyl CoA by either acetoacetate or fumarate

22
Q

How is fumarate converted to acetyl CoA?

A

Fumarate -> malate -> oxaloacetate -> pyruvate -> acetyl CoA

23
Q

What is phenylketonuria?

A

A genetic disease in which phenylalanine hydroxylase enzyme is absent, therefore the body is unable to metabolize phenylalanine to tyrosine

24
Q

What occurs in phenylketonuria instead of phenylalanine metabolism?

A

Phenylalanine is transaminated to phenylpyruvate, which accumulates in the blood and is excreted in the urine

25
Why are phenylalanine and phenylpyruvate harmful?
- They interfere with normal brain and nerve cell development - Phenylalanine competes with other amino acids for uptake in the brain
26
What can elevated phenylalanine levels cause?
Lighter skin colour because the increased phenylalanine inhibits melanin synthesis from tyrosine
27
Which enzyme converts tyrosine to melanin?
Tyrosinase
28
What can phenylpyruvate be converted to?
Phenylacetate or phenyllactate