Introduction
Glycolysis
Figure AV.1: The Glycolytic Pathway.
Now that we have a general understanding of the broad topics of
metabolism and respiration, we will turn our discussion to more specific metabolic
pathways that lead to the derivation of ATP. In this SparkNote we will look
at glycolysis, the metabolism of glucose, a digestive product of
carbohydrates found in many food products that we ingest.
Taking place in the cell
cytoplasm, glycolysis
actually comprises a series of nine steps involving a number of intermediate
structures and specific enzymes that help catalyze each reaction. In this
section, we will go through each of these reactions, learning the roles of the
associated intermediates and enzymes. (Note: specific knowledge of the
nine steps of glycolysis is not necessary for the AP Biology test. In regard to
that test, this summary presents all information necessary about glycolysis and
the first two sections of this SparkNote can be skipped. The third section on
fermentation, however, will be covered on the AP test).
Over the course of glycolysis' nine steps, the 6-carbon molecule glucose is
broken down to two 3-carbon pyruvate molecules. The reaction does not occur
spontaneously: 2 ATP molecules must be broken down to drive the splitting of
glucose into the 2 pyruvates. However, in the course of the breakdown of
glucose, the glycolysis reaction produces four ATP, resulting in a net gain of
two ATP for the entire process. Glycolysis also results in the production of 2
NADH molecules, which eventually play an important role in the production of
additional ATP in the electron transport
chain. Glycolysis itself is
an anaerobic process. After a cell has completed glycolysis, and depending on
the circumstances in which the cell finds itself, that cell can either move into
the process of aerobic respiration and commence the citric acid
cycle or continue with less efficient
aneorobic respiration in a process called
fermentation, covered in
the third section of this SparkNote on glycolysis.
In the first two sections of this SparkNote, we will look at glycolysis in two
major stages. The first involves the phosphorylation of the glucose ring in
preparation for an eventual breakdown into two 3-carbon molecules. In the
second stage, the two 3-carbon molecules are converted into pyruvate.
