General ---------Biology---------------------------------------------------- ------------------Online--------------------------------------- Ch. 9 Cellular Respiration: Harvesting Chemical Energy

Glycolysis is the first pathway of cellular respiration. Glycolysis is followed by the Krebs Cycle and then oxidative phosphorylation.  For overview figure, click here.

Glycolysis is a chemical pathway that functions to split glucose into 2, three carbon molecules of pyruvate.  Although fats, proteins and carbohydrates can all be consumed as fuel, it is traditional to learn the steps of cellular respiration by following glucose through the pathways.   Test Fig. 9.19, The catabolism of various food molecules, illustrates where fats, proteins and carbohydrates enter the various pathways of cellular respiration.

Text Fig. 9.9, A closer look at glycolysis, illustrates glycolysis.  Review the Figure and answer the following questions.

In what steps of the pathway does ATP phosphorylate substrate molecules?  _____ &  _____
In what steps is ADP phosphorylated, producing ATP?  _____ & _____
How many ATP are invested in breaking down glucose? _____
How many ATP molecules are produced* by glycolysis? _____
*Notice the little "2" in the upper left hand corner of the white boxes containing molecules on page 155.  This means there are two molecules proceeding through the pathway after step 4.
What is the ATP "profit" of glycolysis? _____

Notice the 2 NADH molecules that are produced in step 6.  NADH is the "electron dump truck" mentioned in the Introduction.  Visualize NADH as shown below.

Where is NADH going to dump its high energy electrons? (Hint)
a.  glycolysis
b.  Krebs Cycle
c.  Electron transport chain of oxidative phosphorylation

Some important features of glycolysis:

• it can proceed with out oxygen
• but cannot proceed for long if the mitochondria lack oxygen
• if mitochondria lack oxygen they will stop processing pyruvate
• pyruvate will then build up outside of the mitochondria
• if oxygen is not present (anaerobic conditions) pyruvate is converted by enzymes into alcohol in yeast cells and to lactic acid in muscle cells, by a pathway called fermentation
• glycolysis produces two pyruvate, two net ATP and 2 NADH
• it occurs outside the mitochondria

___ What is moving through the chemical pathways, giving off energy in short bursts.
a.  electromagnetic radiation
b.  chemical energy, i.e. high energy electrons stored in covalent bonds
c.  heat
d.  kinetic energy stored in the vibrational motion of the molecules

Text Figure 9.18,Pyruvate as a key juncture in catrabolism, illustrates the fermentation pathway that pyruvate takes if conditions are anaerobic (an = no, aero = air, bios = life).  If oxygen is present, pyruvate moves into the mitochondria and proceeds through the Krebs Cycle.