Concept 7.2 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
There are 2 important roles of glycolysis!
1. To produce energy molecules for the cell to use in its life processes.
2. To produce pyruvate, which can feed the citric acid cycle in the mitochondria of eukaryotes and the cytosol of prokaryotes and ultimately into the electron transport chain where most of the ATP in cellular respiration is produced.
o In glycolysis
(which occurs in the cytosol of all cells with or without oxygen), the degradation of glucose begins as it is broken down into 2 pyruvate molecules. The six-carbon glucose molecule is split into 2 three-carbon sugars through a long series of enzymatically controlled steps.
o In the course of glycolysis, there is an ATP-consuming phase Energy Investment) and an ATP-producing phase (Energy Payoff). In the investment phase, 2 molecules of ATP are consumed which helps destabilize glucose and make it more reactive. Later in the payoff phase 4 ATP molecules are produced resulting in a net gain of 2 ATP molecules during glycolysis. In addition to a net gain of 2 ATP molecules 2 NADH s are produced which will be utilized later in the electron transport system.
o Most of the potential energy of the glucose molecule remains in the two produced pyruvate molecules. If oxygen is present these molecules will be further degraded during the "grooming of pyruvate" (pyruvate oxidation) and the citric acid cycle.
• It is important to note that the staring material for the Citric Acid Cycle is produced during glycolysis!!!!
EVOLUTION CONNECTION
It is presently theorized that glycolysis was the first ATP-producing metabolic pathway to evolve.
There are 3 convincing reasons as to why this theory is probably true!
1. Long ago, Earth's atmosphere contained almost no oxygen, and only relatively recently have the current atmospheric levels of gases come to be what they are.
Glycolysis does not require oxygen, so it is possible that prokaryotes (which evolved before eukaryotes) used this method for making ATP.
1. Glycolysis is a very common method for making ATP; in fact, almost all living organisms use it. This commonality implies that it originated very early in the evolution of metabolic pathways.
2. Glycolysis takes place in the cytosol of all cells not in an organelle Prokaryotic cells, which evolved first, are much simpler than eukaryotic cells, and they contain no membrane-bound organelles. Therefore, if glycolysis were to take place in an early prokaryotic cell, it would have to evolve such that it was capable of taking place in the cytosol-for instance, it would have to evolve such that it did not rely on a specialized membrane in order to function.
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