Amino Acid Degredation

Question 1

Ketogenic

Answer 1

• Amino acids that are degraded to acetoacetyl-CoA / acetyl-CoA
• Will eventually form ketone bodies.

Question 2

Glucogenic

Answer 2

• Amino acids that are degraded to pyruvate, α-ketoglutarate, succinyl-CoA, fumarate, and oxaloacetate
• Will eventually enter citric acid cycle

Question 3

How many amino acids are ketogenic?

Answer 3

7

Question 4

How many amino acids are glucogenic?

Answer 4

18

Question 5

What are the ketogenic amino acids?

Answer 5

• Leucine
• Lysine
• Tyrosine
• Isoleucine
• Phenylalanine
• Threonine
• Tryptophan

Question 6

What are the glucogenic amino acids?

Answer 6

• Alanine
• Arginine
• Asparagine
• Aspartate
• Cysteine
• Glutamine
• Glutamate
• Glycine
• Proline
• Serine
• Histidine
• Methionine
• Valine

Question 7

What are the 5 amino acids that are both glucogenic and ketogenic?

Answer 7

• Tyrosine
• Isoleucine
• Phenylalanine
• Threonine
• Tyrptophan

Question 8

What are the 2 exclusively ketogenic amino acids?

Answer 8

• Leucine
• Lysine

Question 9

What enzymes play an important role in amino acid catabolism?

Answer 9

• Biotin
• THF
• S-adenosylmethionine (adoMet)
  All specialize in one carbon transfer reaction

Question 10

THF (Tetrahydrofolate)

Answer 10

• Two nitrogen atoms are important
• Carbon group undergoing transfer can be bonded to N5, N10 or both
• Three different forms

Question 11

What are the three different forms of THF

Answer 11

1. N5, N10-Methylene-THF
2. N5-Methyl-THF
3. N5, N10-Methenyl-THF

Question 12

N5, N10-Methylene-THF

Answer 12

• Primary source of one carbon units comes from the breakdown of serine to glycine
• Transfers medium oxidized carbons (CH2OH)
• Is interconverted between N5-Methy-THF and N5, N10-Methenyl-THF

Question 13

N5-Methy-THF

Answer 13

Transfers the most reduced carbon (CH3)

Question 14

N5, N10-Methenyl-THF

Answer 14

Transfers a more oxidized carbon (CHO)

Question 15

What is N10-Formyl-THF

Answer 15

Occurs when carbon atom comes from formate instead of serine

Question 16

S-adenosylmethionine (adoMet)

Answer 16

• Preferred cofactor for transfer reactions involving methyl groups
• Synthesized by adenosine and methionine by THF

Question 17

Describe the synthesis of adoMet

Answer 17

1. Methionine + ATP get linked together to form SAM (S-adenosylmethionine)
2. Methyl group from SAM gets transferred to an acceptor to form S-adenosylhomocysteine intermediate
3. S-adenosylhomocysteine is broken down to homocysteine and adenosine
4. Methyl group is transferred to homocysteine by N5-Methyl-THF in a reaction that is catalyzed by methionine synthase (this regenerates methionine)
5. Methionine gets reconverted back into SAM

Question 18

Biotin

Answer 18

Transfers carbon atoms from bicarbonate (HCO3-) in blood in a two step reaction

Question 19

Describe the two step process that is necessary for the one carbon transfer reaction involving Biotin

Answer 19

Biotin is linked to the enzyme biotin carboxylase
- Step 1: Biotin reacts with bicarbonate + ATP to replace H on Nitrogen with a CO2 moiety
- Step 2: The CO2 moiety is transferred to another molecule
(ex: acetyl-CoA) producing a carboxylate group on that molecule
(ex: acetyl-CoA —> malonyl-CoA)

Question 20

What amino acids are degraded to pyruvate?

Answer 20

• Alanine
• Glycine
• Cysteine
• Serine
• Threonine
• Tryptophan

Question 21

What amino acids are degraded to α-ketoglutarate?

Answer 21

• Arginine
• Glutamate
• Glutamine
• Histidine
• Proline

Question 22

What amino acids are degraded to succinyl-CoA?

Answer 22

• Isoleucine
• Methionine
• Threonine
• Valine

Question 23

What amino acids are degraded to fumarate?

Answer 23

• Phenylalanine
• Tyrosine

Question 24

What amino acids are degraded to oxaloacetate?

Answer 24

• Aspartate
• Asparagine

Question 25

What are the branched chain amino acids?

Answer 25

- Leucine - Isoleucine - Valine

Question 26

Describe the degradation of branched chain amino acids

Answer 26

- 2 Steps: - Step 1: Amino acid form ---> Keto acid form (PLP aminotransferase reaction) - Step 2: Keto acid form ---> Final product (Acetyl-CoA, Succinyl-CoA, Acetoaceate) by BCKDH *This is an oxidative decarboxylation reaction*

Question 27

Maple syrup urine disease

Answer 27

- Defective BCKDH enzyme - You cannot successfully metabolize branched chain amino acids which results in the accumulation of these amino acids and their "spill over" into the urine - Result is thick sweet smelling urine

Question 28

Describe the genetic defect that occurs as a result of the inability to break down phenylalanine

Answer 28

- Phenylalanine hydroxylase = first enzyme in the catabolic pathway for phenylalanine (breakdown of phenylalanine to tyrosine) - A defect in the enzyme = PKU disease - Result = elevated levels of phenylalanine in the blood

Question 29

What happens in individuals who have PKU which results in elevated levels of phenylalanine in the blood?

Answer 29

- A normally little-used pathway is activated in which phenylalanine undergoes transamination with pyruvate to yield phenylpyruvate - Phenylalanine and phenylpyruvate accumulate in blood and tissues impairing the normal development of the brain