Cellular Respiration Ch. 9

Overview Respiration has three metabolic stages: Glycolysis Krebs Cycle Electron Transport Phosphorylation Glycolysis and Krebs Cycle decompose glucose and other organic fuels 90% of ATP is produced in Electron Transport Phosphorylation step

Glycolysis Glycolysis means “splitting of sugar” Glucose (6 carbon sugar) is split into two 3-carbon sugars These smaller sugars are oxidized and rearranged to form two molecules of pyruvate Ten total steps in glycolysis First set of steps is “energy investment” Second set of steps is “energy payoff” Net energy gain for every glucose molecule is 2 ATP and 2 NADH

Some energy is made with “substrate-level phosphorylation” Transfer of a phosphate from substrate creates ATP Produces small amount of energy

Krebs Cycle Glycolysis only releases a small amount of the energy in glucose Most of the energy is still stored in the pyruvate If O 2 is present, pyruvate enters mitochondrion where the Krebs Cycle will complete the oxidation of the fuel First thing the mitochondrion will do is convert the pyruvate into acetyl CoA

Step 1: Carboxyl group removed (CO 2 given off) Step 2: Oxidized to form acetate (loses electrons) Step 3: Coenzyme A attached to the acetate

FADH 2 and NADH created by Krebs Cycle will relay electrons to the electron transport chain Also a small amount of ATP created by substrate-level phosphorylation (just like glycolysis)

Electron Transport Phosphorylation Electrons delivered to transport systems of inner mitochondrial membrane As electrons move through the system, they set up H+ gradients, which drive ATP production This is the real “money maker” of ATP production

ATP synthase is powered by the flow of hydrogen ions Like active transport in reverse Can be found in the mitochondrial and chloroplast membranes of eukaryotes Can also be found in plasma membrane of prokaryotes.

Fermentation Anaerobic pathway (does not require O 2 ) Extension of glycolysis that can generate ATP by substrate-level phosphorylation ONLY as long as there is enough NAD+ to accept electrons Pyruvate (end product of glycolysis) serves as an electron acceptor for oxidizing NADH back to NAD+ which can then be reused in glycolysis One example is alcohol fermentation