Cellular respiration takes place in three phases. We have glycolysis, the tricarboxylic acid (TCA) cycle (or fermentation of there is limited oxygen), and then the electron transport chain where the bulk of ATP is produced. I will discuss glycolysis here.
The word glycolysis comes from ‘glyco’ which refers to glucose and ‘lysis’ which means to break up. Therefore, glycolysis is the breakdown of glucose to produce energy and energy-producing molecules. The process takes place in the cytosol of the cell. Glycolysis can be divided into two phases. There is an energy investment phase and an energy payoff phase. Let’s take a look at each of these phases.
The Energy Investment Phase
In this phase, ATP is invested (see sections in green) to get more ATP later in the process. Glycolysis, like many biochemical reactions is highly dependent on enzymes. See enzymes responsible at each step written in red. Notice that glyceraldehyde-3-phosphate and dihydroxyacetone phosphate can be interconverted. However the production of glyceraldehyde-3-phosphate is favored in the reaction since it is constantly being removed to ultimately produced pyruvate.
The Payoff Phase
In this phase, the ATP that was invested yields four more. NADH is also produced, which will be used in another process to produce ATP.
Net Products of Glycolysis
Lets now take a look at the net yield of glycolysis. Put the inputs on the left and the outputs on the right.
Based on the table above, we can write this summary equation.
The two pyruvate molecules made in glycolysis moves on to the TCA cycle where they are converted to generate more ATP and NADH in the energy production process. I will talk about that process next.
To prepare for biochemistry exams it is good to have a visual of the metabolic pathway of glycolysis in your head, including the enzymes involved. Create a mnemonic to help you memorize it.
