1. Glycolysis

2. Glycolysis Overview The Glycolytic pathway describes the oxidation of glucose to pyruvate with the generation of ATP and NADH Glycolysis is a universal pathway; present in all organisms: from yeast to mammals. In eukaryotes, glycolysis takes place in the cytosol Glycolysis is anaerobic; it does not require oxygen. In the presence of O2, pyruvate is further oxidized to CO2. In the absence of O2, pyruvate can be fermented to lactate or ethanol.

3. Glycolysis Eric Niederhoffer SIU-SOM Glucose Pyruvate Lactate 10 steps No O 2 Energy (ATP) and metabolites 3 regulated steps Net Reaction: Glucose + 2NAD+ + 2 Pi + 2 ADP = 2 pyruvate + 2 ATP + 2 NADH + 2 H2O

7. Glycolysis summary Inputs: Glucose 2 NAD+ 2 ATP 4 ADP + 4P Outputs: 2 pyruvate 2 NADH 2 ADP 2 ATP (net gain)

9. Regulation of Glycolysis Steps 1, 3 and 10 are regulatory 1.First regulatory enzyme – Hexokinase (Step 1) Hexokinase catalyses phosphorylation of Glucose > G-6-P First reversible step of glycolysis Glucose >>>>>>> G-6-P (lots) (rate of glycolysis low) so Hexokinase inhibited (Feed back inhibition) Glucose enters cell but since the hexokinase inactive it can readily diffuse back to the blood through the glucose transporter in the plasma membrane. This step uses ATP so prevent wastage.

10. Step 2 Phosphofructokinase Is the rate limiting enzyme Is inhibited by [H+] Production of lactate leads to an increase in [H+] so Phosphofructokinase is inhibited. During vigorous exercise all the lactate can not be removed by the blood leading to a increase in [H+] causing muscle pain. Is inhibited by ATP but stimulated by AMP and Pi This shows that this enzyme is stimulated when the cell needs energy. Is inhibited by citrate Is an early intermediate in the TCA cycle. When the TCA cycle rises citrate is transported out of the mitochondria into the cytosol and inhibits Phosphofructokinase and so slows glycolysis.

11. Step 10 Pyruvate Kinase

12.  Summary of 10 steps StepImportanceEnzymeType 1  Traps glucose inside cell  ATP investment  Regulated 1 HexokinasePhosphoryl transfer 2  Rearrangement Phosphoglucose isomerase Isomerization 3  Rate limiting step ie committed step  ATP investment (second)  Major regulation 2 PhosphofructokinasePhosphoryl transfer 4  Get two, 3 carbon compounds AldolaseAldol cleavage 5  Freely - interconversion Triose phosphate isomerase Isomerization 6  NADH formed i.e. first energy trapping reaction. Glyceraldehyde 3- phosphate dehydrogenase Phosphorylation coupled to oxidation 7  ATP generation (2)  Substrate level Phosphorylation Phosphoglycerate kinase Phosphoryl transfer 8  Phosphoryl shift Phospoglyceromutas e Phosphoryl shift 9  Energy trapping reaction – in the form of PEP. (used to generate ATP in the next rxn) EnolaseDehydration 10  ATP generation (2)  Regulated 3 Pyruvate kinasePhosphoryl transfer

13.  Regulation StepEnzymeInhibitorsStimulators 1HexokinaseEpinephrine + Glucagon (low blood glucose) Insulin 3PhosphofructokinaseATP [H + ] citrate AMP F-2,6-BP(learn in detail) 10Pyruvate kinaseATP Glucagon F1,6-BP (remember is product of Phosphofructokinase)