Cellular respiration is a catabolic pathway done by animals and humans that produce ATP, by consuming oxygen and organic fuel. The oxygen then powers the mighty mitochondrion.
Glucose is the simple sugars which are an important energy source for living organisms, it is taken from the food we eat.
Glucose has to be broken down in order to form pyruvate, this happens because of glycolysis which, occurs in the cytosol. There is a total of 10 steps!
In the first step, when glucose enters the cell and phosphorylated by an enzyme, hexokinase it uses one molecule of ATP. In step two, glucose- 6 phosphates are rearranged to convert it into fructose-6-phosphate. In the 3rd step, Phosphofructokinase transfers a phosphate group from ATP to the sugar, which uses another ATP molecule.
In step 4 the sugar molecule is split into two different 3-carbon sugars: glyceraldehyde-3 phosphate and dihydroxyacetone phosphate. In step 5 isomerase catalyzes the reversible conversion between the two three-carbon sugars
In the second half of glycolysis, G3P is oxidized by transfer of electrons and H+ to NAD+, forming NADH. Since this reaction is very exergonic, the enzyme uses the released energy to attach a phosphate group to the oxidized substrate. ATP is finally being produced, because of the previous step is transferred to ADP.