The tricarboxylic acid (TCA) cycle is a series of enzyme-catalyzed reactions that forms a key part of aerobic respiration in cells. It was discovered by Hans Krebs in 1937 and is also known as the Krebs cycle or citric acid cycle. The cycle occupies a central position in metabolism, using acetate to generate carbon dioxide, reducing agents like NADH, and ATP through oxidative phosphorylation. It provides precursors for amino acid and nucleotide biosynthesis. The cycle is critical for generating the majority of a cell's energy needs through the complete oxidation of carbohydrates, fatty acids, and amino acids.

1. TCA CYCLE
PRESENTED By;
JOSHI UTSAV
MSC SEM-1
ENVIRONMENTAL SCIENCE
HNGU PATAN

2. CONTENT
• TCA CYCLE
DEFINITION
INTRODUCTION
REACTION OF CITRIC ACID CYCLE
SIGNIFICANCE OF TCA CYCLE

3. TCA CYCLE
• Definition:-
 The tricarboxylic acid cycle (TCA CYCLE) is
a series of enzyme catalyzed chemical reactions
that form a key part of aerobic respiration in
cells.
This cycle is also called the Kreb’s cycle and the
Citric acid cycle.

4. INTRODUCTION
The citric acid cycle was discovered by Hans
Kreb’s in 1937 and was also called tricarboxylic
acid (TCA) cycle.
Kreb’s received the Nobel prize in physiology
or medicine in 1953 for his discovery.

5. The TCA cycle Occupies a central position in
metabolism and meet most of cell energy
Requirement by complete oxidation of acetyl-
Co A a key product in the catabolism of
Carbohydrates ,Fatty acid and amino acid to
carbon
dioxide and chemical energy in the form of
guanosine-triphosphate(GTP).
In addition, the cycle provides precursors of
Certain amino acids as well as the reducing agent
NADH that is used in numerous other
biochemical
Reactions.

6. The cycle consumes acetate(in the form of
acetyl-CoA) and water, reduces NAD± to NADH
and produces Co2 as a waste by product. The
NADH generated by the TCA cycle is fed into the
oxidative phosphorylation (electron transport)
pathway.
 In eukaryotic cells, the citric acid cycle occurs in
the matrix of the mitochondrion.

8. REACTION OF CITRIC ACID CYCLE
1) Citrate synthase :- Formation of citroyl CoA
intermediate.

9. 2) Aconitase :- This enzyme catalyses the isomeriz-
ation reaction by removing and then adding back
the water to yield isocitric acid.

10. 3) Isocitrate dehydrogenase :- In the first oxidation
Step of the krebs cycle isocitric acid is oxidatively
Decarboxylated to ∝-ketoglutaric acid.

11. 4) ∝-Ketoglutarate dehydrogenase :- This is a
complex Of different enzymatic activities similar
to the Pyruvate dehydrogenase.

12. 5) Succinyl CoA synthatase :- succinyl CoA like acet-
yl CoA has a thioester bond with very negative free
energy of hydrolysis.
GTP + ADP ----> GDP + ATP.

13. 6) Succinate Dehydrogenase :- oxidation of
succinate to fumarate. This is the only citric acid
cycle enzyme that is tightly bound to the inner
mitochondrial membrane.
It is an FAD dependent enzyme.

14. 7) Fumarase :- The fumaric acid reacts with
molecule of water to form malic acid in the
presence of the enzyme fumarase .

15. 8) L-Malate dehydrogenase :- Oxidation of malate
to oxaloacetate. It is an NAD+ dependent enzyme.

16. SIGNIFICANCE OF TCA CYCLE
1. Intermediate compounds formed during Krebs
cycle are used for the synthesis of biomolecules
like amino acids, nucleotides, chlorophyll,
cytochromes and fats etc.
2. Intermediate like succinyl CoA takes part in the
formation of chlrophyll.
3. Amino Acids are formed from α-Ketoglutaric acid,
pyruvic acid and oxaloacetic acid.
4. Krebs cycle releases plenty of energy required for
various metabolic activities of cell.
5. By this cycle, carbon skeleton are got, which are
used in process of growth and for maintaining the
cells.

17. CONCLUSION
TCA CYCLE :-
ATP Generation
Total ATP = 12 ATP
3 NAD+ = 9 ATP
1 FAD = 2 ATP
1 GDP = 1 ATP

18. REFERENCE
• U. Satyanarayana, Biochemistry, Books and Allied (P) Ltd.,
Calcutta, Latest Edition.
• Frederiksen,M.S. et al (2006), Oxygen dynamics in the
rhizosphere of Zostera marina: A two-dimensional planar
optode study, Limnol Oceanography, vol. 51, 1072 – 1083.
• Gacia,E. et al (2005), Light-dependence of the metabolic
balance of a highly productive Philippine seagrass community,
Experimental Marine Biology and Ecology, vol. 316, 55 – 67.