Krebs Cycle (Citric Acid Cycle)

Biology Pathways Complexity: high
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Description

Citric acid cycle: acetyl-CoA condenses with oxaloacetate and is oxidized through eight steps that release two CO2, three NADH, one FADH2 and one GTP per turn, regenerating oxaloacetate, with isocitrate dehydrogenase gated by the NADH/ATP level.

Process Flowchart

graph TD N1["Acetyl-CoA enters"] N2["Citrate synthase: citrate"] N3["Aconitase: isocitrate"] N4{"NADH / ATP high?"} N5["Isocitrate DH: aKG + NADH"] N6["aKG DH: succinyl-CoA"] N7["Succinyl-CoA -> GTP"] N8["Succinate DH: FADH2"] N9["Fumarase: malate"] N10["Malate DH: OAA + NADH"] N11["OAA regenerated"] N1 --> N2 N2 --> N3 N3 --> N4 N4 -->|proceed| N5 N4 -->|NADH high: slow| N3 N5 --> N6 N6 --> N7 N7 --> N8 N8 --> N9 N9 --> N10 N10 --> N11 N11 -->|next turn| N2 style N1 fill:#ff6b6b,color:#fff style N2 fill:#51cf66,color:#fff style N3 fill:#51cf66,color:#fff style N4 fill:#74c0fc,color:#fff style N5 fill:#51cf66,color:#fff style N6 fill:#51cf66,color:#fff style N7 fill:#51cf66,color:#fff style N8 fill:#51cf66,color:#fff style N9 fill:#51cf66,color:#fff style N10 fill:#51cf66,color:#fff style N11 fill:#b197fc,color:#fff

Node provenance

Each step below is grounded in a cited source (hover a citation for the full title).

StepRoleSource
Acetyl-CoA entersTriggers & InputsBerg, J. M. et al. 2002
Citrate synthase: citrateProcessing & OperationsBerg, J. M. et al. 2002
Aconitase: isocitrateProcessing & OperationsBerg, J. M. et al. 2002
NADH / ATP high?Intermediates & StatesOwen, O. E. et al. 2002
Isocitrate DH: aKG + NADHProcessing & OperationsBerg, J. M. et al. 2002
aKG DH: succinyl-CoAProcessing & OperationsBerg, J. M. et al. 2002
Succinyl-CoA -> GTPProcessing & OperationsBerg, J. M. et al. 2002
Succinate DH: FADH2Processing & OperationsBerg, J. M. et al. 2002
Fumarase: malateProcessing & OperationsBerg, J. M. et al. 2002
Malate DH: OAA + NADHProcessing & OperationsBerg, J. M. et al. 2002
OAA regeneratedProducts & OutputsKrebs, H. A. et al. 1980

🎨 Color Scheme (5-Color System)

Red
Triggers & Inputs
Yellow
Structures & Objects
Green
Processing & Operations
Blue
Intermediates & States
Violet
Products & Outputs

Process Statistics

  • Nodes: 11
  • Edges: 12
  • Conditionals: 1
  • AND Gates: 2
  • OR Gates: 1
  • Total Gates: 3

Keywords

  • citric acid cycle
  • krebs
  • acetyl-coa
  • nadh
  • oxaloacetate

Sources & References

  • Biochemistry, 5th ed. — The Citric Acid Cycle
    Berg, J. M.; Tymoczko, J. L.; Stryer, L. , W. H. Freeman (NCBI Bookshelf, Chapter 17) (2002)
    View Source
  • The key role of anaplerosis and cataplerosis for citric acid cycle function
    Owen, O. E.; Kalhan, S. C.; Hanson, R. W. , Journal of Biological Chemistry (2002)
    DOI: 10.1074/jbc.R200006200
  • The role of citric acid in intermediate metabolism in animal tissues
    Krebs, H. A.; Johnson, W. A. , FEBS Letters (reprint) (1980)
    DOI: 10.1016/0014-5793(80)80029-2