BC 16 Citric Acid Cycle

Cellular Respiration

Process where pyruvate from glycolysis is further oxidized to H2O and CO2.

Citric Acid Cycle

Also called TCA or Krebs cycle; generates 2CO2, 3NADH, FADH2, and one A/GTP.

Coenzyme A

has reactive thiol (--SH) group that carries acyl groups.

Mitochondrial Pyruvate Carrier (MPC)

Moves only pyruvate with H+ across the inner mitochondrial membrane.

Pyruvate Dehydrogenase (PDH) Complex

organized group of enzymes & cofactors in mitochondrial matrix that oxidizes pyruvate to acetyl-CoA and CO2

E1 Enzyme

Pyruvate dehydrogenase; active site has noncovalently bound TPP.

E2 Enzyme

Dihydrolipoyl transacetylase; has an attached lipoate long arm.

E3 Enzyme

Dihydrolipoyl dehydrogenase; contains tightly bound FAD.

Five Coenzymes of PDH

TPP, lipoate, CoA, FAD, and NAD.

Thiamine Pyrophosphate (TPP)

Vitamin B1 / thiamine coenzyme.

Coenzyme A (CoA-SH)

Vitamin B5 / pantothenate coenzyme.

flavin adenine dinucleotide (FAD)

Vitamin B2 / riboflavin coenzyme.

Nicotinamide Adenine Dinucleotide (NAD)

Vitamin B3 / niacin coenzyme.

Substrate Channeling

Passing intermediates directly between enzymes without release.

Nucleoside Diphosphate Kinase

Catalyzes the reversible conversion of GTP and ATP.

Amphibolic Pathway

A pathway that serves in both catabolic and anabolic processes.

Glyoxylate Cycle

Converts acetate to carbohydrates in bacteria, plants, fungi, and protists.

Anaplerotic Reactions

Reactions that replenish intermediates. Enzymes for TCA include pyruvate carboxylase, PEP carboxykinase, PEP carboxylase, and malic enzyme.

Pyruvate Carboxylase

Carboxylates pyruvate by HCO3- to form oxaloacetate; allosterically activated by acetyl-CoA.

Biotin

Vitamin acting as a specialized 1C group carrier in carboxylation.

Biological Tethers

Include lipoate, biotin, and pantothenate.

Regulation Sites in Respiration

PDH, citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase.

Oncometabolites

Stimulate tumor growth by acting through plasma membrane GPCRs.

Metabolons

Multienzyme complexes held together by noncovalent interactions.

Malate dehydrogenase, citrate synthase, and aconitase likely are one together.