Amphibolic nature of kreb's cycle

in this video we are discuss about citric acid cycle catabolic phase and anabolic phase

2. Cells are constantly carrying out thousands of chemical
reactions needed to keep the cell, and your body as a
whole, alive and healthy. These chemical reactions are
often linked together in chains, or pathways. All of the
chemical reactions that take place inside of a cell are
collectively called the cell’smetabolism.
Overview of metabolism

3. Metabolicpathwayscanbebroadlydividedintotwocategoriesbasedon
theireffects.Photosynthesis,whichbuildssugarsoutofsmaller
molecules,isa"buildingup,"oranabolic,pathway.Incontrast,cellular
respirationbreakssugardownintosmallermoleculesandisa"breaking
down,"orcatabolic,pathway.
ATP
ATP
+
+

4. •Containsbothcatabolicandanabolicreactions.
•Catabolic–EnergyfromoxidationofacetylCoAisstoredin
reducedcoenzymes.
•Anabolic–Severalintermediatesareprecursorsin
biosyntheticpathways
Krebs Cycle is Amphibolic

5. Thecitricacidcycle(Krebscycle,Tricarboxylicacidcycle)
includesaseriesofoxidation-reductionreactionsin
mitochondriathatresultintheoxidationofanacetylgroupto
twomoleculesofcarbondioxideandreducethecoenzymesthat
arereoxidizedthroughtheelectrontransportchain,linkedto
theformationofATP
AnoverviewofTCAcycle

6. Citrate
Isocitrate
α
ketoglutarateSuccinylCoA
Succinate
Fumarate
malate
Oxlaoacetate
Acetyl CoA
Pyruvate CO2
Fatty acid
Cholesterol
Amino
Porphyrin
Isoleusine
methionine
valine
Odd chain fatty acid
Aspartate
phenylalanine
tyrosine
Glucose
Acids
•anabolic pathways (red arrows)
•anapleroticreactions replenish depleted
cycle intermediates (dark green arrows).
• Catabolic –Energy from oxidation of
acetyl CoA is stored in reduced coenzymes.
• Anabolic –Several intermediates
are precursors in biosynthetic
pathways.

7. Anaplerosisisaseriesofenzymaticreactionsinwhichmetabolic
intermediatesenterthecitricacidcyclefromthecytosol.
Cataplerosisistheopposite,aprocesswhereintermediatesleave
thecitricacidcycleandenterthecytosol.Inmuscle,anaplerosisis
importantforincreasingcitricacidthroughputduringperiodsof
exercise.
Anaplerosisand Cataplerosis

8. •Thereactioncatalyzedbypyruvatecarboxylasethatreplenishes
oxaloacetatetotheTCAcycleisagoodexampleofananaplerotic,or
“fillingup,”reaction.
•pyruvate+CO2+ATP+H2O→oxaloacetate+ADP+Pi+2H+
•Thisreactionassuresthatthereissufficientoxaloacetatefor
condensationwithacetylCoA.Infact,acetylCoAstimulatespyruvate
carboxylase.
•Thisreactionismostimportant,especiallyinliverandkidney.

9. There is some evidence that anaplerosisis required for a glucose-induced rise in
mitochondrial ATP production. Some amino acids (the building blocks of proteins)
enter and leave the citric acid cycle through anaplerosisand cataplerosis.
Reactions Enzymes Tissue /organism
Pyruvate +HCO3̄̄̄̄̄
+ ATP Pyruvatecarboxylase oxaloacetate + ADP+Pi
Lever, kidney
Phosphoenolpyruvate+CO2+GDP PEPcarboxylase oxaloacetate+GTP Heart,skeletal muscles
Phosphoenolpyruvate+HCO3
PEPcarboxylase oxaloacetate+Pi
Higher plant, yeast,bacteria
Pyruvate +HCO3
+ NADPH malic enzyme malate+NADPH+
Eukaryotes and prokaryotes
AnapleroticReactions

11. Protein may serve an excellent sources of nutrient energy
Catabolism of amino acids provides: succinate, oxaloacetate, fumarate,
αketoglutarate.
Pyruvate (from glycolysis) • acetyl CoA stimulates pyruvate carboxylase
Proteins can also be broken down to feed into the citric acid cycle and generate
energy
Under extreme starvation in animals or during senescence in plants
polypeptides are cleaved to amino acids, amino group is cleaved off of amino
acid forming an organic acid that can enter the citric acid cycle

12. Oxaloacetic
acid
Fumaric
acid Succinic
acid
α
ketoglutarate
Pyruvic
acid
Acetyl
CoA
Alanine, cysteine,
glycine, serine,
threonine, tryptophan
Tryptophan,
leucine, isoleucine
Arginine, Glutamine,
Histidine, Proline
Isoleucine,
methionine,
valine
Phenylalanine,
Tyrosine
Asparagine,
aspartate
NH3 Urea
NH3 Urea
NH3 Urea
NH3 Urea
NH3 Urea
NH3 Urea