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

The Krebs Cycle is a chemical pathway that produces only a few ATP but produces a lot of NADH.

The pathway is illustrated in your text, Fig. 9.11 A closer look at the Krebs cycle.  Look at the pathway and answer the following questions.  Notice that the enzymes that catalyze each step are not listed as they were in glycolysis.  I assume the authors knew there was already a lot of information in the Figure. 

At what steps are carbon dioxide molecules given off?  _____
How many ATP are produced? _____
How many NADH* are produced? _____
At what steps is NAD+ reduced to NADH? __________
At what step is ADP phosphorylated? _____
Write an input-output formula for Step 1.
What does the enzyme at Step 2 do to Citrate to produce Isocitrate?
At Step 4, how many carbons are in the substrate molecule, alpha-Ketoglutarate? ____
At Step 4, how many carbons are in the product molecule, Succinyl CoA? ____
What happened to the missing carbon? ___________________________.

*Notice the FADH at step 6.  FADH is similar to NADH and serves a similar function.  For these questions, assume that FADH is NADH.

It is called a cycle because the starting substrate (oxaloacetate) is the same chemical as the final product.