Week 9 Metabolism Of The Carbon Skelteton

Question 1

WHAT IS THE CARBON SKELETON

Answer 1

Carbon skeleton
α-keto acids (different kinds – depends on the side chain)
Converted into metabolic intermediates:
• Acetyl-CoA
• Acetoacetyl-CoA
• Pyruvate
• Krebs cycle intermediates
Source of energy

Question 2

SUMMARY OF AMINO ACID METABOLISM

Answer 2

The catabolic pathways of each amino acid are different, but they converge on only six compounds.
For some amino acids different parts of the carbon skeleton are used to make different compounds.
Amino acids are glucogenic or ketogenic (or both).
• Glucogenic AA’s can be used to make glucose via gluconeogenesis
• Ketogenic AA’s can be used to make acetyl-CoA

Question 3

REACTIONS IN AMINO ACID CATABOLISM: 1-CARBON TRANSFERS

Answer 3

Different coenzymes involved in transferring a carbon from amino acid substrates:

Biotin transfers carbon as CO2 (highly oxidised). Involved in removal of o2

S-Adenosylmethionine transfers carbon as -CH3 (highly reduced). Transfer carbon alongside hydrogen

Tetrahydrofolate transfers carbon in several oxidation states. Break down all other amino acids that aren’t highly oxidised or reduced
• Note: The oxidised form of tetrahydrofolate is folate (folic
acid), which is vitamin B9.

Question 4

PLP CAN ACT AS A COFACTOR IN SOME 1-C TRANSFER REACTIONS

Answer 4

PLP = can also be used in one carbon metabolism, able to remove co2 from different compounds

Question 5

CATABOLISM OF SIX AMINO ACIDS CONVERGES ON PYRUVATE

Question 6

CATABOLISM OF SEVEN AMINO ACIDS CONVERGES ON ACETYL-COA

Answer 6

The catabolism of tryptophan is the most complex of all the amino acids.
Some parts of the molecule are used in the biosynthesis of other important compounds.

Question 7

CATABOLISM OF FIVE AMINO ACIDS CONVERGES ON A-KETOGLUTERATE

Question 8

CATABOLISM OF FOUR AMINO ACIDS CONVERGES ON SUCCINYL-COA

Question 9

ASPARAGINE AND ASPARTATE ARE OXIDISED TO OXALOACETATE

Answer 9

Asna>Asp is a deamination reaction catalysed by asparaginase.
Asp>aoxaloacetate is achieved through transamination, with α-ketoglutarate being aminated to glutamate at the same time.
In mammals oxaloacetate is converted to malate then transported into the mitochondria, where it can enter the citric acid cycle.