Cellular Respiration Biology 112

Chemical Energy and Food  Food can be broken down into fats, sugars, and proteins  All food is composed of calories – a unit of energy that is needed to raise the temperature of 1g of water 1 o C  Cells use this energy to carry out life activities  This beginning of this process is called glycolysis

The Beginning of the Breakdown of Food - Glycolysis  Releases only a small amount of energy  When oxygen is present, glycolysis leads to two other pathways that release a great deal of energy  If oxygen is not present, it leads to another pathway

Cellular Respiration  The process of breaking down glucose and other food molecules in the presence of oxygen 6O 2(g) + C 6 H 12 O 6(g) → 6CO 2(g) + 6H 2 O (g) + energy  Energy must be released gradually by cells  The release of ATP allows this to happen

The 3 Stages of Respiration  All three stages release ATP from the breakdown of food molecules  Glycolysis takes place in the cytoplasm  Krebs cycle and the electron transport chain takes place in the mitochondria

Glycolysis  One molecule of glucose is broken in half, producing two molecules of pyruvic acid, a 3- carbon compound  this requires two molecules of ATP  Although this is an investment with ATP energy, the cell will release 4 molecules of ATP  A net gain of 2 ATP results – available energy  NADH is also used to release energy for the electron transport chain  It does not require oxygen

What Happens When There is no Oxygen  Glycolysis follows a different pathway  Fermentation releases energy from food molecules by producing ATP in the absence of oxygen  Pyruvic acid is formed, then NADH releases e- to the molecules  ATP can continue being produced  This is an anaerobic process

Alcoholic Fermentation  Yeast undergoes anaerobic fermentation, releasing alcohol, CO 2 and NAD + as products  CO 2 causes bread dough to rise  The alcohol burns off when the bread is baked

Lactic Acid Fermentation (Mammals)  Pyruvic acid may be converted to lactic acid with the release of the NAD +  This can be built up in human muscle when there is not enough oxygen being provided to the tissues  ATP is being produced by the NAD +  This causes a burning sensation and muscles get sore 