Video Transcript
Which of the following best describes the first major reaction that takes place in
glycolysis? (A) A glucose molecule is converted to reduced glucose by the addition of two
hydrogen ions, catalyzed by the oxidation of reduced NAD. (B) A phosphorylated fructose molecule is split into two three-carbon molecules,
known as glyceraldehyde 3-phosphate. (C) A glucose molecule reacts with oxygen to form an unstable six-carbon compound,
which then breaks down into two molecules of glyceraldehyde 3-phosphate, catalyzed
by the hydrolysis of ATP. Or (D) a glucose molecule is converted to phosphorylated fructose by the addition of
two phosphate molecules, catalyzed by the hydrolysis of ATP.
Glycolysis is the term used to describe the first stage of cellular respiration. Cellular respiration is incredibly important for organisms. It is the process by which sugars are broken down to release energy. You may recall the overall chemical equation for cellular respiration: glucose plus
oxygen produces carbon dioxide and water. In this process, energy is released in the form of ATP. Glycolysis takes place in the cytoplasm of cells. The cytoplasm is the jellylike fluid that fills the inside of the cell and contains
most of the cell’s organelles.
Here we have a simple flowchart outlining the major reactions that take place in
glycolysis. The primary reactant of glycolysis is glucose. In the first major reaction of glycolysis, glucose is sequentially phosphorylated by
two molecules of ATP. When a molecule of ATP donates its phosphate group to a different molecule, it is
converted from ATP to ADP. To form ADP, the bond between the second and third phosphate group in ATP breaks. The breaking of this bond using water is known as hydrolysis. The compound that is formed from this reaction is a phosphorylated sugar, more
accurately called phosphorylated fructose or fructose 1,6-bisphosphate.
In the second major reaction of glycolysis, the molecule of phosphorylated fructose
is broken down into two three-carbon compounds called glyceraldehyde 3-phosphate, or
G3P. And in the final major reaction, these three carbon compounds are then converted into
pyruvate, which is the final product of glycolysis. So looking back at our answer choices, we can see that the correct option is (D). In the first major reaction of glycolysis, a glucose molecule is converted to
phosphorylated fructose by the addition of two phosphate molecules, catalyzed by the
hydrolysis of ATP.
