Cellular Respiration

Cells need energy.  To generate this energy they go through several complicated processes in the mitochondria of living cells.  (In the mitochondria of eukaryotic animal cells, that is.  Prokaryotic cells do not have mitochondria.  And eukaryotic plant cells do something else but we haven't talked about that yet.)

The first is glycolysis which occurs in the cytoplasm of cells.  Glycolysis literally means "splitting apart sugar."  That sugar is composed of 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms.  The end products of glycolysis are 2 3-carbon molecules of pyruvic acid and 2 molecules of NADH (NAD+ that has been reduced).  Glycolysis occurs by way of substrate level phosphorylation, which means that a phosphoryl group is added to adenosine diphosphate (ADP) to create adenosine triphosphate (ATP).  Because glycolysis needs 2 ATP to begin and because 4 ATP are created, there is a net gain of 2 ATP.

From glycolysis, pyruvic acid is oxidized to create acetyl CoA.  This means that electrons are taken from pyruvic acid and it loses a carboxyl group.

Then, acetyl CoA moves into the Krebs cycle which occurs in the matrix of the mitochondria.  Here, the carbons in acetyl CoA are released as CO2.  The energy from those released bonds is held as NAD+ and FAD.  Throughout the Krebs cycle NAD+ and FAD are combined with hydrogen electrons to produce NADH and FAD+, respectively.  The added electrons are then passed through the electron transport chain.  A total of 2 ATP are produced by the Krebs cycle.

The electron transport chain is located in the cristae of the mitochondria.  Here, the extra electrons of NADH and FAD+ are passed down a series of transporters.  These transporters are arranged in order from higher affinity for electrons to lower affinity for electrons.  As the electrons are passed from one transporter to another, protons are pumped across the cristae.  This is called a chemiosmotic mechanism.  It creates an energy potential that is collected by ATP synthase and converts ADP to ATP.  The process is called oxidative phosphorylation.  About 32 ATP are created here.

Glycolysis produces 2 ATP, the Krebs cycle produces 2 ATP and the electron transport chain produces 32 ATP for a total of 36 ATP in eukaryotic cells.

At least I hope so, because this is what I'm putting on my first microbiology test in 4 hours.