The TCA Cycle is a series of chemical reactions which helps aerobic organisms to release their energy by oxidation Acetyl CoA to ATP and H20

1. Submitted By:
Name : TRISHNA DAS
Roll No.: 160104016
B.tech 6th Semester
Dept. Of Bioengineering &
Technology

2. • Several of the components and reactions of the citric acid cycle were established
in the 1930s by the research of Albert Szent-Györgyi
received the Nobel Prize in
Physiology or Medicine in 1937
specifically for his discoveries
pertaining to fumaric acid, a key
component of the cycle
• He was able to make this discovery successful
with the help of pigeon breast muscle
• The Citric Acid (TCA) cycle
was finally identified in 1937
by Hans Adolf Krebs and
William Arthur Johnson while
at the University of Sheffield
• Hans Adolf Krebs received the Nobel
Prize for Physiology or Medicine in
1953, and for whom the cycle is
sometimes named (Krebs cycle). Hans Adolf Krebs

3. Overview of The Citric Acid
Cycle
• Also known as Krebs's Cycle
• TheTCA Cycle is the central metabolic hub of the cell
• TheTCA Cycle is the final common oxidative pathway for
carbohydrates, fats, amino acids.
• TCA Cycle supplies energy and also provides many intermediates
required for synthesis of amino acid, heme, etc.
Citric Acid Cycle or The TCA Cycle or Tricarboxylic
Acid cycle essentially involves the oxidation of
acetyl CoA to CO2 and H2O

4. Prokaryotes Eukaryotes
The TCA Cycle occurs in
the cytoplasm
The TCA cycle takes
place in the matrix of the
mitochondria.

5. The overall reaction for
the citric acid cycle is:
2 acetyl groups + 6
NAD+ + 2 FAD + 2 ADP
+ 2 Pi
yields 4 CO2 + 6 NADH
+ 6 H+ + 2 FADH2 + 2
ATP
3C
2C
6C
5C
2C
4C

6. • The first reaction of the cycle is the
condensation of acetyl-
CoA with oxaloacetate to form citrate,
catalyzed by citrate synthase.
Reaction 1: Formation of Citrate
• Once oxaloacetate is joined with acetyl-
CoA, a water molecule attacks the acetyl
leading to the release of coenzyme A
from the complex

7. Reaction 2: Formation of Isocitrate
• The citrate is rearranged to form an
isomeric form, isocitrate by an
enzyme acontinase.
• In this reaction, a water molecule is
removed from the citric acid and then
put back on in another location. The
overall effect of this conversion is that
the –OH group is moved from the 3′
to the 4′ position on the molecule.
This transformation yields the
molecule isocitrate.

8. Reaction 3: Oxidation of Isocitrate to α-
Ketoglutarate
• In this step, isocitrate dehydrogenase
catalyzes oxidative decarboxylation
of isocitrate to form α-ketoglutarate.
In the reaction, generation of NADH
from NAD is seen. The
enzyme isocitrate
dehydrogenase catalyzes the oxidation
of the –OH group at the 4′ position of
isocitrate to yield an intermediate which
then has a carbon dioxide molecule
removed from it to yield alpha-
ketoglutarate.

9. Reaction 4: Oxidation of α-Ketoglutarate to
Succinyl-CoA
• Alpha-ketoglutarate is oxidized,
carbon dioxide is removed, and
coenzyme A is added to form the 4-
carbon compound succinyl-CoA.
• During this oxidation, NAD+ is reduced
to NADH + H+. The enzyme that
catalyzes this reaction is alpha-
ketoglutarate dehydrogenase.

10. Reaction 5: Conversion of Succinyl-CoA to
Succinate
• CoA is removed from succinyl-
CoA to produce succinate.
• The energy released is used to make
guanosine triphosphate (GTP) from
guanosine diphosphate (GDP) and Pi
by substrate-level phosphorylation.
GTP can then be used to make
ATP. The enzyme succinyl-CoA
synthase catalyzes this reaction of the
citric acid cycle.

11. Reaction 6: Oxidation of Succinate to
Fumarate
• Succinate is oxidized to fumarate.
• During this oxidation, FAD is reduced
to FADH2. The enzyme succinate
dehydrogenase catalyzes the removal
of two hydrogens from succinate.

12. Reaction 7: Hydration of Fumarate to Malate
• The reversible hydration
of fumarate to L-malate is catalyzed
by fumarase (fumarate hydratase).
Fumarase continues the rearrangement
process by
adding Hydrogen and Oxygen back into
the substrate that had been previously
removed.

13. Reaction 8: Oxidation of Malate to
Oxaloacetate
• Malate is oxidized to
produce oxaloacetate, the starting
compound of the citric acid
cycle by malate dehydrogenase.
During this oxidation, NAD+ is
reduced to NADH + H+.

14. ATP Generation:
• 3 NAD+ = 9 ATP
• 1 FAD = 2 ATP
• 1 ATP = 1 ATP
Total ATP = 12 ATP

15. The Uses of Citric Acid in the Food Industry
Citric Acid is found in
• Citrus fruits like Oranges, lemons and grapefruits.
• Peppers, tomatoes and most berries.
The food industry utilizes citric acid in a much different fashion, with its
marvelous acid fermenting, catalyzing, preserving, and flavoring foods
and beverages.
• Cheese Manufacturing: – The cheese industry uses citric acid,
particularly with mozzarella. It utilizes citric acid as a catalyst to
quickly ferment milk. Faster fermentation means large-scale
operations can create cheese more rapidly

16. • Shelf Life: Because citric acid reduces the pH to levels too low for most bacteria, the
shelf life of processed foods increases dramatically for jams and jellies, canned foods,
meat products, and other foods.
• Taste: Along with preserving carbonated beverages, teas, and juices, citric acid adds the sour or
acidic flavor consumers enjoy.
• Emulsifier: Citric acid acts as a vegetable fat emulsifier.
• Effervescence:When coupled with sodium bicarbonate, citric acid effervesces. Fizzy candies,
carbonated beverages, and powdered drinks, as well as antacid tablets and powders, owe their
effervescence to this chemical reaction. In fact, approximately 50% of citric acid production is
utilized in beverages.
Beer &Wine: Because citric acid is a weak acid, it is often utilized to create an acidic
environment in beer and wine production.

17. Citric Acid in carbonated drinks
Citrc acid is used in Jams to increase Shelf Life
Fizzy candies

18. References:
1. http://nobelprize.org/nobel_prizes/medicine/laureates/1937/
2. Biochemistry Textbook by Lubert Stryer
3. Lehninger Principles of Biochemistry. 5th Edition. Chapter 15 :The Citric Acid Cycle.
4. THE CITRIC ACID (KREBS) CYCLE Learning Objectives for this Section
http://faculty.ccbcmd.edu/biotutorials/cellresp/cac.html
5. https://sciencing.com/cytoplasm-function-and-facts-13714432.html (Image)
6. Krebs (Citric Acid) Cycle Steps by Steps Explanation
https://microbiologyinfo.com/krebs-citric-acid-cycle-steps-by-steps-explanation/
7. http://www.bellchem.com/news/the-uses-of-citric-acid-in-the-food-industry