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MBOD Week 13 > Urea Cycle; Synthesis of Amino Acids > Flashcards

Urea Cycle; Synthesis of Amino Acids Flashcards

1
Q

What is the byproduct of amino acid degradation in the fasting state?

A

Lots of Nitrogen

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2
Q

Where does glutamine go to get deanimated?

A

The liver

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3
Q

What liver enzymes turn glutamate to alpha-ketoglutarate?

- Reaction type?

A
  • Glutaminase - Deanimation

- Glutamate Dehydrogenase - Deanimation

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4
Q

What enzyme deaminates alanine in the liver?

A

ALT

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5
Q

The amino group from what amino acid is used in the Urea Cycle?

A
  • Alanine

* Note: this comes from deamination via ALT

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6
Q

What is the point of the Alanine cycle?

A

To convert Alanine to pyruvate for Gluconeogenesis

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7
Q

What tissues are nourished by glucose made in the Alanine cycle during the fasting state?

A
  • Brain

- Red Blood Cells

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8
Q

What amino acid collects the amino groups that are taken from Alanine and other amino acids during the urea cycle?

A

Glutamate

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9
Q

What are the 3 key amino acids in the urea cycle?

A
  1. Glutamine
  2. Glutamate
  3. Alanine
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10
Q

Although NH4+ is the predominant form of ammonia following decarboxylation, why is NH3 also important?

A

Because it can cross membranes such as the BBB

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11
Q

What are some of the consequences of having too much ammonia in the blood (normal = 30-60 um)?

A
  1. Ammonia can cross the BBB (high levels are toxic)
  2. Alpha Ketoglutate (important in TCA) and glutamate (Neurotransmitter) are depleted as they get converted to Glutamine

**Overall it affects neurotransmitter and TCA

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12
Q

Where does most nitrogen disposal take place?

A

Urea Cycle in LIVER

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13
Q

Where does the Urea cycle occur?

A
  • In mitochondria and cytoplasm

* ALL of it occurs in the liver

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14
Q

How many nitrogens are disposed of with each urea?

A

2

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15
Q

T or F: the urea cycle results in a net gain of energy in the cell

A

False, Making Urea is an Energetically Expensive process

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16
Q

What is the source of the first and seconds nitrogens in the urea cycle?

A
  1. Carbomoyl Phosphate

2. Aspartate

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17
Q

What is BUN a measure of?

A

The amount of Urea in the blood

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18
Q

When would a patient of high BUN?

A

Renal Failure

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19
Q

What does low BUN mean?

A

There is probably some type of deficiency

in enzyme or substrate

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20
Q

What is the most common urea cycle defect?

A
  • OTC deficiency
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21
Q

What is the physiologic result from OTC deficiency?

A
  • Blood ammonia levels are really high, NO detectable Citrulline, and HIGH Oroate
  • Result is mental retardation
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22
Q

What is the treatment for OTC deficiency?

A
  1. Low-protein diet

2. Drugs that react with amino acids

23
Q

What drugs react with amino acids do to help treat OTC deficiency?
- why does it work?

A
  • Benzoic acid and phenylbutyrate
  • These bind amino acids then are peed out
  • New nitrogen is used to make amino acids , thus pulling it out of the blood
24
Q

What are the 2 possible fates of oroate when there is an OTC deficiency?

A
  1. Could be used to make pyrimidines

2. Excreted in urine (this is how it is detected)

25
Q

What enzyme is responsible for turning ammmonia into Carbamoyl Phosphate?

A

CPSI

26
Q

How would you distinguish a CPSI deficiency from an OTC deficiency?

A
  • The type of breakdown product

- Carbamoyl Phosphate will not be present in CPSI deficiency (oroate probably won’t be present either)

27
Q

What enzyme is responsible for making citrulline?

A

OTC

28
Q

What disease results from defective phenylalanine hydroxylase enzyme?

A

Phenylketoneuria (PKU)

29
Q

What intermediate would be expected to be elevated in PKU?

A

Phenylalanine

30
Q

What kind of diet would someone with PKU need?

A
  • Diet Low in Phenylalanine and high in tyrosine
31
Q

What type of coefactor is used in most aminotransferases?

A

PLP

32
Q

What is the coefactor for Tyrosine Aminotransferase?

A

PLP

33
Q

What disease results from deficient Tyrosine Aminotransferase?

A

Tyrosinemia II

34
Q

What products build up in tyrosinemia II?

A
  • Tyrosine and Phenylalanine

- That’s why you treat these patients with low tyrosine and low Phenylalanine diet

35
Q

What disease results from Homogentisate Oxidase deficiency?

A

Alcaptonuria

36
Q

What are the side effects and symptoms of alcaptonuria?

A
  1. Urine turns dark when exposed to air

2. Arthritis may develop later in life due to pigment build up

37
Q

What is the precursor for Serine?

A
  • 3-Phosphoglycerate

* THIS IS A GLYCOLYTIC INTERMEDIATE*

38
Q

What is the precursor for Alanine?

A

Pyruvate

39
Q

What is the precursor for Glycine?

A

Serine

40
Q

T or F: The reaction of Serine —> Glycine catalyzed by Serine Hydroxymethyl Transferase is reversible

A

True

41
Q

What coefactors are needed to convert Serine to glycine?

A

PLP and Tetrahydrofolate (FH4)

42
Q

What is the most common purpose of FH4 (tetrahydrofolate) in enzymes?

A
  • It moves 1 carbon groups
43
Q

Where is folate obtained and what is the most common form in the body?

A
  • Obtained from leafy vegetable, fruits, and legumes

- FH4 the fully reduced form is most common

44
Q

Why does folate deficiency lead to neural tube defects?

A
  • It inhibits DNA synthesis
45
Q

What metabolic disorder results from inability to make Cysteine?

A

Homocysteinemia - High Homocysteine in blood

46
Q

What enzyme is likely deficient in Homocysteminemia?

A
  • Enzyme converting Homocysteine to Cystathione

- Enzyme = CBS (don’t have to know name)

47
Q

What are two possible causes of Homocysteinemia?

A
  1. CBS (enzyme deficiency preventing Homocysteine –> Cystathione)
  2. FH4 or B12 deficiency (prevents homocysteine —> Methionine)

**Two possible causes means you can’t pinpoint the problem just by having high levels of homocysteine in the urine

48
Q

T or F: homocysteine can be used as a marker of Cardiovascular Disease

A

True

49
Q

Is Homocysteinuria observed when someone has Homocysteinemia?

A

NO, homocystinuria IS though

50
Q

What is classical homocysteinemia?

A
  • Results from an enzyme deficiency
51
Q

How can classical homocyteinemia be differentiated from that which results from B12 or Folate insufficiency?
-would blood or urine testing be better for diagnosis?

A

Methionine will build up indicating B12 and FH4 are still working

  • YOU HAVE TO TEST BLOOD, methionine will not show up in urine
52
Q

What are two symptoms of Homocysteinemia?

A
  1. Dislocated Optic Lenses

2. Abnormal Blood Clotting - tissues have infarcts

53
Q

How shoul classic homocysteinemia be treated?

A
  • Diet Low in Met

- Oral B6 works for about 50% of people

54
Q

Where does the source of Arginine in the cell come from?

A

The urea cycle

MBOD Week 13 (7 decks)

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