8.2.pdf

Glycolysis Overview: Common pathway for breaking down glucose in bacteria, eukaryotes, and archaea. Produces energy, electron carriers, and building blocks for cell metabolism. An ancient and universal process found in all living organisms. Oxygen Use: Glycolysis doesn’t r...

Glycolysis Overview: Common pathway for breaking down glucose in bacteria, eukaryotes, and archaea. Produces energy, electron carriers, and building blocks for cell metabolism. An ancient and universal process found in all living organisms. Oxygen Use: Glycolysis doesn’t require oxygen but can work with oxygen or without (aerobic or anaerobic processes). Location: Occurs in the cytoplasm of both prokaryotic and eukaryotic cells. Process: Starts with one six-carbon glucose molecule. Ends with two three-carbon pyruvate molecules. Pyruvate can be further broken down for more energy; some organisms rely only on glycolysis for ATP production. Types of Glycolysis: The most common type in animals and many microbes is the Embden-Meyerhof-Parnas (EMP) pathway. Phases of Glycolysis: 1. Energy Investment Phase: ○ Uses 2 ATP to modify glucose, splitting it into two three-carbon molecules (G3P). 2. Energy Payoff Phase: ○ Converts G3P to pyruvate, producing 4 ATP and reducing 2 NAD+ to NADH. ATP Production: ATP is generated through substrate-level phosphorylation, where a phosphate is transferred directly to ADP to form ATP. Net Gain from Glycolysis: 2 ATP molecules 2 NADH molecules 2 pyruvate molecules Other Glycolytic Pathways  Glycolysis usually refers to the EMP pathway in animals and many bacteria. Some bacteria (prokaryotes) use different glycolytic pathways: ○ Entner-Doudoroff (ED) Pathway: Discovered by Nathan Entner and Michael Doudoroff. Used by some bacteria like Pseudomonas aeruginosa. E. coli can use either ED or EMP pathways. Pentose Phosphate Pathway (PPP): ○ Found in all cells, different from the EMP and ED pathways. ○ Considered one of the oldest glycolytic pathways. ○ Provides intermediates for making nucleotides and amino acids. ○ Important for cells that need to produce nucleic acids or proteins. Glycolysis produces pyruvate, which can be further broken down to release more energy. Transition Reaction (Bridge Reaction): Pyruvate is converted into a two-carbon acetyl group by the enzyme pyruvate dehydrogenase. This process also produces NADH from NAD+. Acetyl group must attach to Coenzyme A (CoA) to proceed. Occurs in the mitochondrial matrix in eukaryotes and in the cytoplasm in prokaryotes. Krebs Cycle (Citric Acid Cycle or TCA): Takes place in the mitochondrial matrix of eukaryotes and the cytoplasm of prokaryotes. Electrons from the acetyl group are transferred to electron carriers. Named after Hans Adolf Krebs. Closed loop cycle; the end regenerates the starting compound. Produces: ○ 2 CO2 molecules ○ 1 ATP (or GTP) ○ 3 NADH ○ 1 FADH2 The acetyl group combines with a four-carbon compound to form citric acid. Function: Used in glucose metabolism. Intermediates can synthesize various important molecules like amino acids, fatty acids, and nucleotides. The cycle is both anabolic (building up) and catabolic (breaking down).