GLYCOLYSIS (“Sugar-breaking”) **During Glycolysis, 1 molecule of Glucose (which has 6 carbons), is transformed into 2 molecules of Pyruvic Acid (which has 3 carbons). **As the bonds in glucose are broken and rearrange, energy is release. GLUCOSE PYRUVIC ACID PYRUVIC ACID

1. Glycolysis takes a little energy to get started. 2 ATP molecules ATP PRODUCTION: 1. Glycolysis takes a little energy to get started. 2 ATP molecules are used up. 2. Glycolysis produces 4 ATP. This gives the cell a net gain of 2 ATP for each molecule of glucose. NADH PRODUCTION: Glycolysis removes 4 electrons from the molecule. 2. The electrons are passed to NAD+ (electron carrier) NAD+ can carry a pair of electrons. 2 NAD+ are required to carrier the 4 electrons to the electron transport chain (3rd stage) where the electrons are used to produce ATP.

Summary of Glycolysis -4 ATP molecules are made from 4 ADP molecules. -There is a net gain of 2 ATP since 2 ATP are used to start glycolysis. -2 ATP is not a lot BUT glycolysis happens very fast so a cell can produce thousands of ATP in a few milliseconds. -It does not require oxygen (anaerobic). -Pyruvic acid moves to the Krebs Cycle (2nd Stage). -NADH moves to the Electron Transport Chain (3rd Stage).

THE KREBS CYCLE (Citric Acid Cycle) The Krebs Cycle is the second stage of cellular respiration which operates only when oxygen is available. The Krebs cycle is a series of energy-extracting reactions.

Summary of The Krebs Cycle: 1. Pyruvic acid produced by glycolysis enters mitochondria. In the innermost compartment of a mitochondrion, or the matrix, pyruvic acid molecules are broken down into carbon dioxide and acetyl-CoA molecules. 2. Acetyl-CoA combines with a 4-carbon compound, producing a 6-carbon molecule—citric acid. Energy released by the breaking and rearranging of carbon bonds is captured in ATP, NADH, and FADH2. 3. The Krebs cycle produces four types of products: -high-energy electron carriers (NADH and FADH2) -carbon dioxide -2 ATP molecules (per glucose molecule) -the 4-carbon molecule needed to start the cycle again