Cellular Respiration

Chemical Pathways

Essential Questions What is cellular respiration? What happens during the process of glycolysis? What are the two main types of fermentation?  

Organisms use food 1. as the chemical building blocks they need to grow and reproduce 2. as a source of raw materials from which the cells of the body can synthesize new molecules 3. as a SOURCE OF ENERGY

Organisms release the energy in glucose and other compounds gradually, in a series of reactions

The process of releasing energy from glucose begins with GLYCOLYSIS; 1. if oxygen is present this leads to a two-step pathway releasing a great deal of energy 2. if oxygen is not present, glycolysis is followed by a different pathway

CELLULAR RESPIRATION is the process that releases energy by breaking down glucose (GLYCOLYSIS) in the presence of oxygen, followed by the KREBS CYCLE and the ELECTRON TRANSPORT CHAIN   Equation is 6O2 + C6H12O6 → 6CO2 + 6H2O + energy

3 Main Stages of Cellular Respiration 1. GLYCOLYSIS-process in which 2 ATPs are used to break down one molecule of glucose is broken to produce 2 molecules of pyruvic acid, and 4 molecules of ATP (for a net gain of 2 ATP) Note that glycolysis does not require oxygen; if oxygen is not present, NAD+ may run out, stopping glycolysis (NAD+ is an electron carrier to a later step) is very fast occurs in the cytoplasm

The energy released during cellular respiration is used to form ATP

2. KREBS (CITRIC ACID) CYCLE-to be discussed in Sect. 9.2

3. ELECTRON TRANSPORT CHAIN-to be discussed in Sect. 9.2

When oxygen is not present, glycolysis is followed by FERMENTATION, an ANAEROBIC (without oxygen) process occurs in which NADH passes high energy electrons back to pyruvic acid, so that glycolysis can continue producing ATP; two types of fermentation

1. ALCOHOLIC FERMENTATION-yeasts and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol and carbon dioxide as wastes pyruvic acid + NADH → alcohol + CO2 + NAD+ occurs in rising bread dough, alcoholic beverages

LACTIC ACID FERMENTATION-occurs in animal muscles, some unicellular organisms as pyruvic acid is converted to lactic acid during rapid exercise when sufficient oxygen cannot be supplied; produces muscle burning and soreness; also occurs to produce cheese, yogurt, buttermilk, sour cream, pickles, sauerkraut, kimchi