河南师范大学：《生物化学》课程PPT教学课件（英文版）Section L Respiration and Energy

Section L Respiration and Energy L1 Citric acid cycle L2. Electron transport and oxidative hosphorylation L3. Photosynthesis

L1. Citric acid cycle L2. Electron transport and oxidative hosphorylation L3. Photosynthesis Section L Respiration and Energy

Citric acid cycle Role Location The cycle Energy yield Regulation Biosynthetic pathways

• Role • Location • The cycle • Energy yield • Regulation • Biosynthetic pathways Citric acid cycle

Role The Citric acid柠檬酸 cycle, also known as the TcA( (tricarboxylic acid三羧酸) cycle or Krebs cycle (after its discover in 1993), is used to oxidize the pyruvate formed during the glyco lytic breakdown of glucose into CO2 and H2o The cycle is a major energy source in the form of ATP and also produces precursors for many biosynthetic pathways

Role • The citric acid柠檬酸cycle ,also known as the TCA (tricarboxylic acid三羧酸) cycle or Krebs cycle (after its discover in 1993), is used to oxidize the pyruvate formed during the glyco￾lytic breakdown of glucose into CO2 and H2O. The cycle is a major energy source in the form of ATP and also produces precursors for many biosynthetic pathways

Location The citric acid cycle occurs within the mitochondria of eukaryotes and the cytosol of prokaryotes

Location • The citric acid cycle occurs within the mitochondria of eukaryotes and the cytosol of prokaryotes

The cycle Step 1. Oxidation of fuel molecules to acetyl CoA A major source of energy is glucose which is converted by glycolysis into pyruvate. Pyruvate dehydrogenase(a complex of three enzymes and five coenzymes)then oxidizes the pyruvate(using NAD which is reduced to NADH) to form acetyl CoA and Co. since the reaction involves both an oxidation and a loss of CO2, the process is called oxidative decarboxylation

The cycle • Step 1 .Oxidation of fuel molecules to acetyl CoA • A major source of energy is glucose which is converted by glycolysis into pyruvate. Pyruvate dehydrogenase (a complex of three enzymes and five coenzymes ) then oxidizes the pyruvate (using NAD+ which is reduced to NADH ) to form acetyl CoA and CO2 since the reaction involves both an oxidation and a loss of CO2 , the process is called oxidative decarboxylation

E Acetyl-CoA CHc oxidized lipoyllysine TPP FAD TPP FAD cO E NADH+H+ O HS FAD TPPE1 Ez NAD oxidized Hipoyllysine reduced lipoyllysine oA-SH TPPE EFAD用 HS HA E E CHa SCoA TPP FAD AcetyI-CoA

Acetyl-CoA

The citric acid cycle The cycle carries out the oxidation of acetyl groups from acetyl CoA to cO, with the production of four pairs of electrons, stored initially in the reduced electron carriers NadH and FAdH

• The cycle carries out the oxidation of acetyl groups from acetyl CoA to CO2 with the production of four pairs of electrons, stored initially in the reduced electron carriers NADH and FADH2 The citric acid cycle

Cvcle mode Acetyl-COA Oxaloacetate Isocitrate NADH cO 2 H NADH Malnte a-Ketoglutarate 2 NAD Fumarate L-COA FADH? GTP CATP)

Cycle mode

EIGHT STAGES The citric acid cycle has eight stages: (1)Production of citrate from oxaloacetate(7 酰乙酸) and acetyl CoA( catalyzed by citrate synthase) COoH CH3 H2-COOH co+co→HOC-CooH H2 H2-COOH COOH COA

EIGHT STAGES • The citric acid cycle has eight stages: • (1)Production of citrate from oxaloacetate (草 酰乙酸) and acetyl CoA (catalyzed by citrate synthase) • COOH CH3 CH2-COOH • CO + CO HO-C-COOH • CH2 S CH2-COOH • COOH CoA

Citrate formation HO COA-SH CH4-C+0=C-00 S-CoA CH2-000 Citrate AG=-822 k I/mol

Citrate formation