Biochemistry: Energy Storage and Citric Acid
Cycle (CAC) - Exam Q&A
Citric Acid cycle - ANSWERAlso known as Krebs cycle after its discoverer Sir
Hans Krebs, and as the tri-carboxylic acid (TCA) cycle based on the structure
of citric acid
-The CAC oxidizes a 2C acetyl group completely to CO2, producing energy
directly as GTP, and indirectly as NADH and FADH2
-Central biochemical pathway, and is amphibolic (meaning in participates in
Anabolism and Catabolism)
Stage 1 - ANSWER-Production of acetyl CoA from pyruvate
-3C pyruvate changed into 2C acetyl by complex enzyme known as pyruvate
decarboxylase by an oxidative decarboxylation
-Energy is derived from the PDHase reaction in the form of NADH. The
reaction combines with the acetyl product with a carrier, Coenzyme A, to
make acetyl coA for entry into the CAC
Pyruvate Dehydrogenase - ANSWERPDH is made of three enzyme units:
-E1: Pyruvate dehydrogenase
-E2: a transacetylase
-E3: another dehydrogenase
The PDH complex is made of multiple copies of each enzyme plus associated
cofactors to form an assembly line
, PDH Reaction - ANSWERPyruvate + CoASH + NAD+ ---> Acetyl-CoA + CO2 +
NADH
-Decarboxylation + Redox rxn
-Produces 1 NADH molecule and CO2
1. Citrate synthase - ANSWERCondensation reaction
-Adds 2C Acetyl CoA to 4C oxaloacetate to form 6C citrate
-Citrate synthase enzyme
-Acetyl CoA added to the alpha-carbon of oxaloacetate
2. Aconitase - ANSWERIsomerization Reaction
-Citrate isomerized to isocitrate
-Aconitase is enzyme
-Occurs between C2 and C3: OH and H of C2 and C3 respectively switch
positions with one another
-Dehydration followed by rehydration
3. Isocitrate Dehydrogenase - ANSWERFIRST oxidative decarboxylation
-Reduces number of C's by 1
-Isocitrate converted to alpha-ketoglutarate by removing carbonyl group
-Isocitrate dehydrogenase is enzyme
-decarboxylation + Redox, as seen in production of Acetyl CoA
4. Alpha-ketoglutarate dehydrogenase - ANSWERSECOND oxidative
decarboxylation
Cycle (CAC) - Exam Q&A
Citric Acid cycle - ANSWERAlso known as Krebs cycle after its discoverer Sir
Hans Krebs, and as the tri-carboxylic acid (TCA) cycle based on the structure
of citric acid
-The CAC oxidizes a 2C acetyl group completely to CO2, producing energy
directly as GTP, and indirectly as NADH and FADH2
-Central biochemical pathway, and is amphibolic (meaning in participates in
Anabolism and Catabolism)
Stage 1 - ANSWER-Production of acetyl CoA from pyruvate
-3C pyruvate changed into 2C acetyl by complex enzyme known as pyruvate
decarboxylase by an oxidative decarboxylation
-Energy is derived from the PDHase reaction in the form of NADH. The
reaction combines with the acetyl product with a carrier, Coenzyme A, to
make acetyl coA for entry into the CAC
Pyruvate Dehydrogenase - ANSWERPDH is made of three enzyme units:
-E1: Pyruvate dehydrogenase
-E2: a transacetylase
-E3: another dehydrogenase
The PDH complex is made of multiple copies of each enzyme plus associated
cofactors to form an assembly line
, PDH Reaction - ANSWERPyruvate + CoASH + NAD+ ---> Acetyl-CoA + CO2 +
NADH
-Decarboxylation + Redox rxn
-Produces 1 NADH molecule and CO2
1. Citrate synthase - ANSWERCondensation reaction
-Adds 2C Acetyl CoA to 4C oxaloacetate to form 6C citrate
-Citrate synthase enzyme
-Acetyl CoA added to the alpha-carbon of oxaloacetate
2. Aconitase - ANSWERIsomerization Reaction
-Citrate isomerized to isocitrate
-Aconitase is enzyme
-Occurs between C2 and C3: OH and H of C2 and C3 respectively switch
positions with one another
-Dehydration followed by rehydration
3. Isocitrate Dehydrogenase - ANSWERFIRST oxidative decarboxylation
-Reduces number of C's by 1
-Isocitrate converted to alpha-ketoglutarate by removing carbonyl group
-Isocitrate dehydrogenase is enzyme
-decarboxylation + Redox, as seen in production of Acetyl CoA
4. Alpha-ketoglutarate dehydrogenase - ANSWERSECOND oxidative
decarboxylation
