This document summarizes key aspects of metabolic pathways involving glucose-6-phosphate, pyruvate, acetyl CoA, and the tricarboxylic acid (TCA) cycle. It discusses the fates and oxidation of glucose-6-phosphate, pyruvate, and acetyl CoA through glycolysis, gluconeogenesis, glycogenolysis, the HMP shunt, the Cori cycle, and the TCA cycle. It also describes the enzymes, regulation, energetics, anabolic and amphibolic roles of the TCA cycle. The complete oxidation of one glucose molecule through these pathways produces a total of 32 ATP molecules.

1. Metabolic fate of
Glu-6-P, Pyruvate & Acetyl CoA.
TCA cycle/ Krebs cycle / Citric acid cycle
Dr. Santhosh Kumar N
Associate Professor of Biochemistry
“Believe yourself ”
Have a great day to all

2. 2
Glycogenesis
Glycolysis Gluconeogenesis
HMP
shunt
Glycogenolysis 1
2
3
4a
4b
Fate of Glu-6-P

3. Gly, Ala, val, Pro, Ser, Asp, Arg ,
Glu, Cys, Thr, His, Met , Gln, Asp
Glucose
Cori cycle
Acetaldehyde
Ethanol
TCA
Cycle
1
2 3
4
5
6 7
Fate of Pyruvate

4. Pyruvate Dehydrogenase Complex
E1. Pyruvate dehydrogenase
E2: Dihydrolipoamide transacetylase
E3: Dihydrolipoamide dehydrogenase

5. PDH Complex

6. Tri-carboxylic acid (TCA cycle) /
Krebs cycle
/ Citric acid cycle

7. • The citric acid cycle is the central metabolic hub of the cell.
• It is the gateway to the aerobic metabolism of any molecule that can be
transformed into an acetyl group or dicarboxylic acid.
• The aerobic processing of glucose starts with the complete oxidation to CO2.
• This oxidation takes place in the citric acid cycle, a series of reactions known as
the “tricarboxylic acid (TCA) cycle” or the “Krebs cycle”.

8. TCA cycle is the final common pathway for the oxidation
of fuel molecules – amino acids, carbohydrates & fatty
acids that enter the cycle as acetyl CoA
The enzymes of citric acid cycle are located in the
mitochondrial matrix.

9. Fluoro acetate
NADH, Arsenate,
Succinyl-CoA
10ATPs ADP
Malonate
+Pi

10. Energetics of TCA cycle
Isocitrate dehydrogenase (NADH+H+ =2.5ATPs) +2.5 ATP
α-Ketoglutarate Dehydrogenase (NADH+H+) + 2.5ATP
Succinyl Thiokinase [1GTP = 1ATP)] + 1 ATPs
Succinate Dehydrogenase [FADH2 = 1.5 ATP)] + 1.5 ATPs
Malate Dehydrogenase (NADH+H+) +2.5 ATP
one molecule of acetyl CoA produced no. of ATPs in TCA cycle 10 ATPs

11. Regulation of TCA cycle
• α-ketoglutarate dehydrogenase is inhibited by NADH, Succinyl-CoA and
Arsenate.
• Aconitase enzyme is inhibited by fluoro acetate
• The key enzymes of the TCA cycle are also regulated allosterically by Ca2+, ATP
and ADP.

12. Significance of the TCA Cycle
• Final common oxidative pathway and integration of major metabolic
pathways
• It is the source of reduced coenzymes that provide the substrate for the
respiratory chain
• Provides the precursors for the building blocks of many molecules such as
amino acids, Nucleotide bases (Purines & Pyrimidines) and Porphyrin
• It act as a link b/w catabolic & anabolic pathways (amphibolic role)

13. Anabolic role of TCA cycle
It provides the intermediates for the synthesis of many compounds

14. Anaplerotic reaction of TCA cycle
• filling up reactions which supply intermediates of TCA cycle .
1
2
3
4
5
6

15. Malate DH
Amphibolic nature of TCA cycle

16. ATPs
Fatty Acids
Amino Acids
Glucose
Conversion of food to energy to run cellular processes
ATP servers as the energy currency of the cells

17. Pathways Total ATPs
A. Glycolysis 7 ATPs
B. Oxidative decarboxylation of 2 pyruvate to 2 Acetyl CoA [2 x NADH] 5 ATPs
C. TCA cycle (2 moles of acetyl CoA involved 2x10) 20ATPs
one molecule of glucose produced total ATPs 32 ATPs
Energetics on complete oxidation of glucose:

18. Acetyl CoA
Synthesis of
Cholesterol
Acetylation reactions
(Detoxification)
Synthesis of Melatonin
Formation of Acetylcholine
Formation of
Ketone Bodies
Oxidation of TCA cycle
Denovo synthesis of FA
HMG -CoA
PYRUVATE
Acetylation of amino- sugars ,
glycoprotein
Ketogenic
a.a’s
β-Oxidation
of FA
Cytoplasmic
Synthase &
Reductase
Mitochondrial
Synthase &
lyase
Fate of Acetyl CoA

19. Dreams Don’t’ work,
Unless YOU DO