This document discusses the tricarboxylic acid (TCA) cycle and the glyoxylate cycle. It defines the TCA cycle as a series of reactions that forms a key part of aerobic respiration. The cycle was discovered by Hans Krebs in 1937 and involves the oxidation of acetyl-CoA derived from carbohydrates, fats, and amino acids. The glyoxylate cycle is a variation that occurs in plants, bacteria, and fungi and allows the conversion of acetyl-CoA into carbohydrates from acetate. It bypasses two decarboxylation steps in the TCA cycle using the enzymes isocitrate lyase and malate synthase. The document outlines the reactions and significance of both cycles

1. TCA CYCLE AND GLYOXYLATE CYCLE
Presented By..
Patel Rinku D.
M.sc (sem-3)Botany.
CBO-501.
Department of life sciences,
H.N.G.U.,PATAN.

2. CONTENTS
• TCA CYCLE
 DEFINITION
 INTRODUCTION
 REACTION OF CITRIC ACID CYCLE
 SIGNIFICANCE OF TCA CYCLE
• GLYOXYLATE CYCLE
DEFINITION
INTRODUCTION
SIGNIFICANCE OF GLYOXYLATE CYCLE
 NET REACTION
CONCLUSION

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 krebs cycle and the
Citric acid cycle.

4. INTRODUCTION
The citric acid cycle was discovered by Hans
Krebs in 1937 and was also called tricarboxylic
acid (TCA) cycle.
Krebs 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 molec-
ule 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. GLYOXYLATE CYCLE
• DEFINITION :-
 The glyoxylate cycle, a variation of the tricarboxy-
lic acid cycle, is an anabolic pathway occuring in
plants, Bacteria, protists and fungi. The glyoxylate
cycle centers on the conversion of acetyl-CoA to
succinate for the synthesis of carbohydrates.

18. INTRODUCTION
Glyoxylate cycle occur in some micro-organisms
When acetate is sole source of carbon.
This cycle has two unique enzyme-isocitrate lyase
and malate synthase which bypass some of the
reaction of TCA cycle.

20.  Glyoxylate cycle is absent in higher organism.
 The Glyoxylate cycle utilizes five of the eight enzy-
mes associated with the tricarboxylic acid cycle :-
• Citrate synthase, aconitase,succinate dehydrogen-
ase ,fumarase and malate dehydrogena.
The bypass consists of 2 reactions, namely :-
(a) Splitting of isocitrate into Succinate and glyoxylate, and
(b) Conversion of glyoxylate into malate.

21.  This bypasses the decarboxylation steps that
place in the TCA cycle, allowing simple carbon
compounds to be used in the later synthesis of
macromolecules, including glucose.
Malate is also formed in parallel from succinate
by the action of succinate dehydrogenase and
fumarase.

22. SIGNIFICANCE OF GLYOXYLATE CYCLE
1. It is Bypass reaction of TCA cycle.
2. It occurs in bacteria when they are cultured in
acetate rich carbon source.
3. When Higher fatty acids are oxidized into acetyl
CoA without forming pyruvate acids, then acetyl
CoA enters into glyoxylate cycle.

23. NET REACTION
• Net Reaction of TCA Cycle :-
Acetyl CoA + 3 NAD+ + FAD + GDP + Pi + 2 H2O
2 CO2 + CoA + 3 NADH + FADH2 + GTP
2H+
• Net Reaction of Glyoxylate Cycle :-
2 acetyl CoA + NAD+ Succinate + 2 CoA +
NADH + H+

24. CONCLUSION
TCA CYCLE :-
ATP Generation
Total ATP = 12 ATP
3 NAD+ = 9 ATP
1 FAD = 2 ATP
1 GDP = 1 ATP
GLYOXYLATE CYCLE :-
ATP Generation
Total ATP = 5 ATP
1 NAD+ = 3 ATP
1 FAD = 2 ATP

25. REFERENCE
 Plant physiology
V.verma.
 Fundamental of Biochemistry
By , Dr. J. L. Jain
Dr. Sanjay Jain
Nitin Jain
 Principles of Biochemistry
By , ALbert-Leningher
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