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Intro to Biochemistry > 29 - Amino Acid Metabolism > Flashcards

29 - Amino Acid Metabolism Flashcards

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1
Q

is alanine essential or non-essential? Glucogenic, ketogenic or both?

A

Non-essential

glucogenic

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2
Q

Is asparagine essential or non-essential? Glucogenic, ketogenic or both?

A

non-essential

glucogenic

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3
Q

Is aspartic acid essential or non-essential? Glucogenic, ketogenic or both?

A

non-essential

glucogenic

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4
Q

Is cysteine essential or non-essential? Glucogenic, ketogenic or both?

A

non-essential

glucogenic

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5
Q

is glutamic acid essential or non-essential? Glucogenic, ketogenic or both?

A

non-essential

glucogenic

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6
Q

is glutamine essential or non-essential? Glucogenic, ketogenic or both?

A

non-essential

glutogenic

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7
Q

is glycine essential or non-essential? Glucogenic, ketogenic or both?

A

non-essential

glutogenic

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8
Q

is proline essential or non-essential? Glucogenic, ketogenic or both?

A

non-essential

glutogenic

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9
Q

is serine essential or non-essential? Glucogenic, ketogenic or both?

A

non-essential

glucogenic

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10
Q

is tyrosine essential or non-essential? Glucogenic, ketogenic or both?

A

non-essential

both

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11
Q

is ornithine/taurine essential or non-essential? Glucogenic, ketogenic or both?

A

non-essential

both

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12
Q

is arginine essential or non-essential? Glucogenic, ketogenic or both?

A

essential (but insufficient synthesis)

glucogenic

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13
Q

is histidine essential or non-essential? Glucogenic, ketogenic or both?

A

essential

both

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14
Q

is isoleucine essential or non-essential? Glucogenic, ketogenic or both?

A

essential

both

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15
Q

is leucine essential or non-essential? Glucogenic, ketogenic or both?

A

essential

ketogenic

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16
Q

is lysine essential or non-essential? Glucogenic, ketogenic or both?

A

essential

ketogenic

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17
Q

is methionine essential or non-essential? Glucogenic, ketogenic or both?

A

essential (but insufficient synthesis)

glucogenic

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18
Q

is phenylalanine essential or non-essential? Glucogenic, ketogenic or both?

A

essential (but insufficient synthesis)

both

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19
Q

is threonine essential or non-essential? Glucogenic, ketogenic or both?

A

essential

both

20
Q

is tryptophan essential or non-essential? Glucogenic, ketogenic or both?

A

essential

both

21
Q

is valine essential or non-essential? Glucogenic, ketogenic or both?

A

essential

glucogenic

22
Q

Which amino acids can be broken down in the human body?

A

all

23
Q

When amino acids are degraded, where do their components go?

A

The carbon skeleton is converted into energy metabolites and the amino group goes into urea (in the liver) for excretion

24
Q

What are transaminases? What are transaminations?

A

These convert the amino group on an amino acid with a keto group on a ketoacid (like alpha-ketoglutarate)

For example, alanine and alpha-ketoglutarate can be converted to glutamate and pyruvate with transaminase.

This is a transaminatino reaction.

All transaminases have pyridoxal phosphates as a prosthetic group,

pyridoxal phosphates are derived from pyridoxine (vitamin B6)

Transaminases are also called aminotransferases.

25
Q

What ensures that transaminations of aspartate/oxaloacetate continue?

A

Antiporters for glutamate and aspartate. This way aspartate is stuck in the cytosol to react with glutarate and form oxaloacetate (transamination) to feed into gluconeogenesis.

26
Q

What is important about aspartate aminotransferase?

A

The transamination of alpha-ketoglutarate + aspartate to glutamate + oxaloacetate

This is a step to make oxaloacetate that will be used in gluconeogenesis. This must happen in the cytosol, because oxaloacetate can’t be transported into cytosol form mitochondria, but aspartate can.

27
Q

What is the malate aspartate shuttle?

A

Import of NADH into mitochondria for use in oxidative phosporylation achieved by converting between aspartate/glutamate and oxaloacetate/malate (converting from malate to oxaloacetate in mitochondria generates an NADH)

28
Q

What enzyme catalyzes oxidative deamination and reductive amination of glutamate/alpha-ketoglutarate in mitochondrial matrix?

A

glutamate dehydrogenase

Reversible reaction: direction determined by reactant concentrations (including ammonium and pH)

29
Q

How is glutamine synthesized?

A

Glutamine acts as an amino group carrier
- Glutamine synthetase converts glutamate + ammonium to glutamine (costs ATP) which forms an amide bond

This is an irreversible reaction

30
Q

What enzyme catalyzes the conversion of glutamine to glutamate?

A

Glutaminase

31
Q

What happens to carbon skeletons from the degradation of glucogenic amino acids?

A

Used for pyruvate or TCA cycle intermediates

Useful for anaplerosis and gluconeogenesis

32
Q

What happens to carbon skeletons form degradation of ketogenic amino acids?

A

Converted to acetyl-CoA (energy substrate), but not for gluconeogenesis or anaplerotic reactions

33
Q

What is the transsulfuration pathway?

A

Breakdown of methionine. It is important for the generation of S-adenosyl methionine (SAM)

Linked to tetrahydrofolate metabolism

Methionine metabolism is connected to :one-carbon metabolism” transmethylations

34
Q

What is the precursor for tetrahydrofolate (THF)?

A

Vitamin B9, folic acid, synthesized by microorganisms.

Synthesis from folate is catalyzed by dihydrofolate reductase

35
Q

What does tetrahydrogolate (THF) do?

A

Transfers C1 groups in several oxidation states

Used for

  • Amino acid synthesis
  • Purine synthesis
  • Thymidine monophosphate synthesis
36
Q

What happens if there is a folate deficiency?

A

Unable to make THF, used in amino acid synthesis, purine synthesis and thymidine monophosphate synthesis

Results in
- Neural tube defects and anemia

Deficiency is usually due to increased demand and poor absorption or drugs that inhibit dihydrofolate reductase

37
Q

What does vitamin B12 (cobalamine) do?

A

Can convert various amino acids (valine, isoleucine and threonine) as well as odd chain fatty acids which have been converted to methylmaalonyl-CoA to succinyl CoA

Also can convert homocysteine to methionine, homocysteine has a role in methylgroup transfer reactions.

38
Q

How are branched chain amino acids broken down?

A

Transamination to a ketoacid and then decarboxylation with BCKD (using NAD+ and CoASH)

39
Q

What does a defect in BCKD cause?

A

BCKD catalyzes the decarboxylation of branched chain amino acids (after they’ve been transminated)

A defect leads to maple syrup urine disease. This eventually leads to brain damage and death

40
Q

What does the glucose-alanine cycle do?

A

Gets rid of excess nitrogen:

  1. Alanine is transported to the liver and transminated with alpha-ketoglutarate to glutamate and pyruvate
  2. Part of the glutamate is oxidatively deaminated by glutamate dehydrogenase to alpha-ketoglutarate and ammonium
  3. part of the glutamate is transaminated to aspartate
  4. aspartate and NH4 go into urea synthesis
41
Q

What is the urea cycle?

A

Where aspartate and ammonium from the glucose-alanine cycle in converted to urea for excretion.

In terrestrial vertebrates most nitrogen must be excreted (a little is used in biosynthetic reactions)

Urea cycle is in liver

42
Q

Where do the two amino groups of urea come from?

A

One comes from Ammonium and the other comes from aspartate

43
Q

What are the steps of the urea cycle?

A
  1. Synthesis of carbamoyl phosphate
  2. Entry into cycle:transer of carbamoyl group to ornithine
  3. Second aminogroup from aspartate
  4. Fumarate formation
  5. Formation of urea, regeneration of ornithine
44
Q

The urea cycle is linked to what other cycle and how?

A

The urea cycle is linked to the citric acid cycle. Fumarate made in the urea cycle enters the citric acid cycle and is converted to oxaloacetate needed for transamination.

45
Q

What is usually happening when there is a negative nitrogen balance (more nitrogen going out than in)?

A
  • Starvation
  • Serious illness
  • Insufficient essential amino acids
46
Q

What is usually happening when there is a positive nitrogen balance (more nitrogen going in than out)?

A
  • Growth
  • Pregnancy
  • Recovery from illness or starvation
47
Q

What can alpha-keto acids from transamination of amino acids (in their degradation) be precursors for?

A

CO2 and H2O
GLucose
Ketones and fatty acids

Intro to Biochemistry (28 decks)

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