Week 9 Metabolism Of The Carbon Skelteton Flashcards
WHAT IS THE CARBON SKELETON
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
SUMMARY OF AMINO ACID METABOLISM
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
REACTIONS IN AMINO ACID CATABOLISM: 1-CARBON TRANSFERS
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.
PLP CAN ACT AS A COFACTOR IN SOME 1-C TRANSFER REACTIONS
PLP = can also be used in one carbon metabolism, able to remove co2 from different compounds
CATABOLISM OF SIX AMINO ACIDS CONVERGES ON PYRUVATE
CATABOLISM OF SEVEN AMINO ACIDS CONVERGES ON ACETYL-COA
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.
CATABOLISM OF FIVE AMINO ACIDS CONVERGES ON A-KETOGLUTERATE
CATABOLISM OF FOUR AMINO ACIDS CONVERGES ON SUCCINYL-COA
ASPARAGINE AND ASPARTATE ARE OXIDISED TO OXALOACETATE
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.