The citric acid cycle (also known as the Krebs cycle or TCA cycle) is a series of oxidation-reduction reactions in mitochondria that oxidizes acetyl groups and reduces coenzymes, which are then reoxidized to generate ATP. The cycle takes place in the mitochondrial matrix and is the primary step of aerobic processing in eukaryotic cells. It oxidizes glucose, fatty acids, and amino acids to carbon dioxide while collecting electrons to produce NADH and FADH2, which power the electron transport chain to generate ATP. The cycle was discovered by Hans Krebs in 1937 and is the central metabolic hub of the cell.

1. CITRIC ACID
C
Citric acid cycle
(CAC) can be also be
called Krebs cycle or
even Tricarboxylic
Acid cycle (TCA)
CYCLE
By
Joel Sau Paul

2. Overview of the citric
acid cycle
The citric acid cycle includes a series of
oxidation-reduction reactions in mitochondria
that results in the oxidation of acetyl group
to two molecule of carbon dioxide and
reduce the coenzymes that are reoxidized
through the electron transport chain , linked
to the formation of ATP.

3.  The Krebs cycle can also be called the citric acid cycle (
CAC) or the Tricarboxylic Acid (TAC) cycle.
 The citric acid cycle is the central metabolic hub of the cell
 This cycle takes place in MITOCHONDRIAL MATRIX and is the
primary step of aerobic processing within a cell .
 In eukaryotes the reaction of the citric acid cycle takes
place inside mitochondria ,in contrast with those of
glycolysis ,which take place in cystol.
 The process oxidizes glucoses glucose derivatives fatty acids
and amino acids to carbon dioxide through a series of
enzyme controlled steps.

4.  The purpose of the Krebs cycle is to collect high energy
electrons from these fuels by oxidizing them which are
transported by activated carriers NADH and FADH2 to the
electron transport chain.
 It is the final common pathway for the oxidation of fuel
molecule such as amino acids, fatty acids and
carbohydrates.
 The Krebs cycle is also a source of many other molecules
and is and is therefore an amphibolic pathway ( anabolic
and catabolic).

5. HISTORY
Citric acid cycle was discovered by Hans
Krebs in 1937
He received the Nobel Prize in
physiology or medicine in 1953 for his
discovery
He was Forced to leave Germany prior to
WWII because he was Jewish

6. KERBS CYCLE

7. FULL FORMS OF TERMS
 NAD - Nicotinamide adenine dinucleotide
 NADH- Nicotinamide adenine dinucleotide
hydrate
 FADH - Flavin adenine dinucleotide hydrate
 FAD - Flavin adenine dinucleotide
 GDP – guanosine di phosphate
 GTP – guanosine tri phosphate

8. Step 1
Pyruvate Acetyl CoA
• 3 carbon pyruvate converted to 2 carbon
acetyl CoA
• PYRUVATE is derived from the glycolysis of
glucose which is a 6 carbon compound
• here the pyruvate is oxidized into a acetyl
CoA IN the presence of pyruvate
dehydrogenase complex as a catalyst
• The by product is 1 molecule of co2 and also
NADH gets oxidized to NAD+

9. Step 2 ACETYL CoA + OXALOACETATE
CITRATE
• 2 carbon acetyl CoA (along +
with) 4 carbon oxaloacetate
combines to give 6 carbon
citrate
• The reaction happens in the
presence of catalyst Citrate
Synthase .

10. Step 3 Citrate Isocitrate
In this step
6 Carbon citrate is directly
converted into 6 carbon
ISOCITRATE in the presence of
catalyst
ACONITASE

11. Step 4 Isocitrate ALFA-
KETOGLUTARATE
• The 6C isocitrate is oxidized to
5C Alfa- Ketoglutarate in the
presence of
isocitrate
dehydrogenase
• in this reaction NAD+ is reduced
to NADH
and 1 carbon is lost as
byproduct CO2 is liberated.

12. Step 5 ALFA-KETOGLUTARATE SUCCINYL CoA
• The 5C Alfa- Ketoglutarate is
oxidized to 4C SUCCINYL CoA
in the presence of
Alfaketoglutrate
Dehydrogenase.
• in this reaction like wise in
previous reaction NAD+ is
reduced to NADH
and 1 carbon is lost as
byproduct CO2 is liberated
forming 4C SUCCINYL CoA.

13. Step 6 SUCCINYL CoA SUCCINATE
In this step
• 4C Succinyl CoA is converted
into 4C Succinate in the
presence of
Succinyl CoA synthase
• in this reaction GDP
( guanosine di
phosphate)becomes GTP
(guanosine tri phosphate )

14. Step 7 SUCCINATE FUMARATE
• 4C Succinate is converted
into 4C fumarate in the
presence of
Succinyl dehydrogenase
• in this reaction FAD is
reduced to FADH2
and hence maintaining
the number of carbons

15. Step 8
FUMARATE MALATE
• 4C fumarate is
converted into
4C Malate in
the presence of
Fumrase

16. Step 9 MALATE OXALOACETATE
• The 4C MALATE is
converted to 4C
OXALOACETATE in the
presence of
MALATE
Dehydrogenase.
• in this reaction like wise
in previous reaction
NAD+ is reduced to NADH
HENCE THE CYCLE
CONTINUES ……… !

17. THANK YOU