The document discusses the tricarboxylic acid (TCA) cycle, also known as the Krebs cycle or citric acid cycle. It provides three key points:
1. The TCA cycle involves the oxidation of acetyl-CoA to carbon dioxide and water and is the final common pathway for carbohydrates, fats, and amino acids.
2. The cycle generates energy in the form of ATP, NADH, and FADH2 and provides precursors for biosynthesis.
3. The cycle occurs in the mitochondrial matrix and is tightly regulated by enzymes and cellular energy levels to integrate major metabolic pathways.
The citric acid cycle, also known as the tricarboxylic acid cycle (TCA cycle) or the Krebs cycle—is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate—derived from carbohydrates, fats, and proteins—into carbon dioxide.
Pentose phosphate pathway is also called Hexose monophosphate pathway/ HMP shunt/ Phosphogluconate pathway.
It is an alternative route for the metabolism of glucose.
It is more complex pathway than glycolysis.
It is more anabolic in nature.
It takesplace in cytosol.
The tissues such as liver, adipose tissue, adrenal gland, erythrocytes,testes and lactating mammary gland are highly active in HMP shunt.
It concern with the biosynthesis of NADPH and pentoses.
Glycogenolysis, process by which glycogen, the primary carbohydrate stored in the liver and muscle cells of animals, is broken down into glucose to provide immediate energy and to maintain blood glucose levels during fasting. These slides will provide you detail explanation of Glycogenolysis.
The citric acid cycle, also known as the tricarboxylic acid cycle (TCA cycle) or the Krebs cycle—is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate—derived from carbohydrates, fats, and proteins—into carbon dioxide.
Pentose phosphate pathway is also called Hexose monophosphate pathway/ HMP shunt/ Phosphogluconate pathway.
It is an alternative route for the metabolism of glucose.
It is more complex pathway than glycolysis.
It is more anabolic in nature.
It takesplace in cytosol.
The tissues such as liver, adipose tissue, adrenal gland, erythrocytes,testes and lactating mammary gland are highly active in HMP shunt.
It concern with the biosynthesis of NADPH and pentoses.
Glycogenolysis, process by which glycogen, the primary carbohydrate stored in the liver and muscle cells of animals, is broken down into glucose to provide immediate energy and to maintain blood glucose levels during fasting. These slides will provide you detail explanation of Glycogenolysis.
The citric acid cycle – also known as the TCA cycle or the Krebs cycle – is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA
citric acid cycle or TCA cycle.
krebs cycle is amphibolic in nature and its important reactions.
occurs in mitochondrial matrix in close proximity to ETC.
5 types of vitamins are involved in this cycle. also inhibitors are present . regulation of TCA cycle is governed by mainly 3 enzymes
and there is mention the energies of every step that takes place in citric acid cycle.
citric acid cycle produces 24 molecules of ATP in every cycle
1. INTRODUCTION
TCA cycle (tricarboxylic acid cycle) or the Krebs cycle is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins which oxidizes to CO2 and H2O.
TCA cycle is used by organisms that respire to generate energy, either by anaerobic respiration or aerobic respiration.
Site : Mitochondrial matrix
2.Reactions
1. Condensation of acetyl CoA and oxaloacetate to citric acid.
2a. Dehydration of citric acid to cis-aconitate.
2b. Hydration of cis-aconitate to isocitrate.
3. Oxidative decarboxylation of isocitrate to α-ketoglutarate.
4. Oxidative decarboxylation of α-ketoglutarate to succinyl CoA.
5. Substrate level phosphorylation of succinyl CoA to succinate.
6. Dehydrogenation of succinate to fumarate.
7. Hydration of fumarate to malate.
8. Dehydrogenation of malate to oxaloacetate.
3. Significance of TCA cycle
Complete oxidation of acetyl CoA.
ATP generation.
Final common oxidative pathway.
Integration of major metabolic pathways.
Fat is burned on the wick of carbohydrates.
Excess carbohydrates are converted as neutral fat
No net synthesis of carbohydrates from fat.
Carbon skeleton of amino acids finally enter the TCA cycle.
4. Energetics of TCA Cycle
Oxidation of 3 NADH by ETC coupled with oxidative phosphorylation results in the synthesis of 9 ATP.
FADH2 leads to the formation of 2ATP.
One substrate level phosphorylation.
Thus, a total of 12 ATP are produced from one acetyl CoA.
5. Regulation of TCA Cycle
Three regulatory enzymes
Citrate synthase
Isocitrate dehydrogenase
α-ketoglutarate dehydrogenase
Citrate synthase is inhibited by ATP, NADH, acyl CoA & succinyl CoA. Isocitrate dehydrogenase is activated by ADP & inhibited by ATP and NADH α-ketoglutarate dehydrogenase is inhibited by succinyl CoA & NADH. Availability of ADP is very important for TCA cycle to proceed.
6. Inhibitors of TCA Cycle
Aconitase is inhibited by fluoro-acetate. This is a non-competitive inhibition.
Alpha ketoglutarate is inhibited by Arsenite. This is also a non-competitive.
Succinate dehydrogenase is inhibited by malonate. This is competitive inhibition.
7. Amphibolic nature of the TCA cycle
TCA cycle is both catabolic & anabolic in nature, called as amphibolic.
Since various compounds enter into or leave from TCA cycle, it is sometimes called as metabolic traffic circle.
8. References
Textbook of Biochemistry-U Satyanarayana
Textbook of Biochemistry- DM Vasudevan
1. The citric acid cycle (CAC) – also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle– is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.
2. For each turn of the cycle, three NADH, one ATP( through GTP) and one FADH2 are created.
The all the content in this profile is completed by the teachers, students as well as other health care peoples.
thank you, all the respected peoples, for giving the information to complete this presentation.
this information is free to use by anyone.
TCA cycle overview
Glycolysis converts glucose to pyruvate
Produces 2 molecules of 2ATP per glucose
Large amounts of potential energy from glucose remains unused
Aerobic oxidation of pyruvate ensures that this energy is not lost
The TCA cycle is the final common pathway for the oxidation of fuel molecules such as amino acids, fatty acids and carbohydrates
The cycle is also an important source of precursors, not only for the storage forms of fuel, but also for the building blocks of many other molecules such as amino acids, nucleotides bases and sterols
The citric acid cycle is the central metabolic hub of the cell.
It is the final common pathway for the oxidation of fuel molecule such as amino acids, fatty acids, and carbohydrates.
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2. TCA Cycle
Also known as Krebs cycle
TCA cycle essentially involves the oxidation of
acetyl CoA to CO2 and H2O.
TCA cycle –the central metabolic pathway
The TCA cycle is the final common oxidative
pathway for carbohydrates, fats, amino acids.
3. TCA cycle supplies energy & also provides many
intermediates required for the synthesis of amino
acids, glucose, heme etc.
TCA cycle is the most important central pathway
connecting almost all the individual metabolic
pathways.
4. Definition
Citric acid cycle or TCA cycle or tricarboxylic acid
cycle essentially involves the oxidation of acetyl
CoA to CO2 & H2O.
Location of the TCA cycle
Reactions of occur in mitochondrial matrix, in
close proximity to the ETC.
5. Reactions of TCA cycle
Oxidative decarboxylation of pyruvate to acetyl
CoA by PDH complex.
This step is connecting link between glycolysis and
TCA cycle.
6. Reactions of TCA Cycle
Step:1 Formation of citrate
Oxaloacetate condenses with acetyl CoA to form
Citrate, catalysed by the enzyme citrate synthase
Inhibited by:
ATP, NADH, Citrate - competitive inhibitor of
oxaloacetate.
7. Steps 2 & 3 Citrate is isomerized to isocitrate
Citrate is isomerized to isocitrate by the enzyme
aconitase
This is achieved in a two stage reaction of
dehydration followed by hydration through the
formation of an intermediate -cis-aconiase
8. Steps 4 & 5 Formation of -ketoglutarate
Isocitrate dehydrogenase (ICDH) catalyses the
conversion of (oxidative decarboxylation) of isocitrate
to oxalosuccinate & then to -ketoglutarate.
The formation of NADH & the liberation of CO2
occure at this stage.
Stimulated (cooperative) by isocitrate, NAD+, Mg2+,
ADP, Ca2+ (links with contraction).
Inhibited by NADH & ATP
9. Step: 6 Conversion of -ketoglutarate to
succinyl CoA
Occurs through oxidative decarboxylation,
catalysed by -ketoglutarate dehydrogenase
complex.
-ketoglutarate dehydrogenase is an multienzyme
complex.
At this stage of TCA cycle, second NADH is
produced & the second CO2 is liberated.
10. Step: 7 Formation of succinate
Succinyl CoA is converted to succinate by
succinate thiokinase.
This reaction is coupled with the phosphorylation
of GDP to GTP.
This is a substrate level phosphorylation.
GTP is converted to ATP by the enzyme nucleoside
diphosphate kinase.
11. Step: 8 Conversion of succinate to fumarate
Succinate is oxidized by succinate dehydrogenase
to fumarate.
This reaction results in the production of FADH2.
Step: 9 Formation of malate: The enzyme
fumarase catalyses the conversion of fumarate to
malate with the addition of H2O.
12. Step:10 Conversion of malate to
oxaloacetate
Malate is then oxidized to oxaloacetate by malate
dehydrogenase.
The third & final synthesis of NADH occurs at this
stage.
The oxaloacetate is regenerated which can
combine with another molecule of acetyl CoA &
continue the cycle.
14. Regeneration of oxaloacetate
The TCA cycle basically involves the oxidation of
acetyl CoA to CO2 with the simultaneous
regeneration of oxaloacetate.
There is no net consumption of oxaloacetate or any
other intermediate in the cycle.
15. Significance of TCA cycle
Complete oxidation of acetyl CoA.
ATP generation.
Final common oxidative pathway.
Integration of major metabolic pathways.
Fat is burned on the wick of carbohydrates.
Excess carbohydrates are converted as neutral fat
No net synthesis of carbohydrates from fat.
Carbon skeleton of amino acids finally enter the TCA cycle.
16. Requirement of O2 by TCA cycle
There is no direct participation of O2 in TCA cycle.
Operates only under aerobic conditions.
This is due to, NAD+ & FAD required for the
operation of the cycle can be regenerated in the
respiratory chain only in presence of O2.
Therefore, citric acid cycle is strictly aerobic.
17. Energetics of TCA Cycle
Oxidation of 3 NADH by ETC coupled with
oxidative phosphorylation results in the synthesis of
9ATP.
FADH2 leads to the formation of 2ATP.
One substrate level phosphorylation.
Thus, a total of 12 ATP are produced from one
acetyl CoA.
18.
19. Regulation of TCA Cycle
Three regulatory enzymes
1. Citrate synthase
2. Isocitrate dehydrogenase
3.α-ketoglutarate dehydrogenase
20. Citrate synthase is inhibited by ATP, NADH, acyl
CoA & succinyl CoA.
Isocitrate dehydrogenase is activated by ADP &
inhibited by ATP and NADH
α-ketoglutarate dehydrogenase is inhibited by
succinyl CoA & NADH.
Availability of ADP is very important for TCA
cycle to proceed.
21. Transamination
Transamination is a process where an amino acid
transfers its amino group to a keto group and itself
gets converted to a keto acid.
The formation of Alpha ketoglutarate &
oxaloacetate occures by this mechanism.
