Chapter 5_3 Cellular Respiration

Bell Ringer In your notebook, answer the following questions (You may use your Biology Textbook): How are the products of photosynthesis and respiration related? What kinds of organisms undergo cellular respiration?

Cellular Energy The transfer of energy in organic compounds to ATP through a process called Cellular Respiration. Aerobic Respiration – metabolic processes that requires oxygen. Anaerobic Respiration – metabolic process that do not require oxygen.

Stages of Cellular Respiration C6H12O6 + 6O2 __enzymes__> 6CO2 + 6H2O + energy ATP Glucose is converted to pyruvate, producing a small amount of ATP and NADH. Cellular Respiration BEGINS with a Biochemical Pathway called GLYCOLYSIS, that takes place in the Cells Cytosol, YIELDS a relatively Small amount of ATP and does not require oxygen In the presence of oxygen, pyruvate and NADH are used to make a large amount of ATP. The Second Stage of Cellular Respiration is called AEROBIC RESPIRATION, and follows Glycolysis. Aerobic Respiration takes place within the Mitochondria.  This is far more effective than Glycolysis at recovering energy from food molecules.

Because they operated in the Absence of Oxygen, the THERE ARE TWO TYPES OF CELLULAR RESPIRATION:  AEROBIC (PRESENCE OF OXYGEN) AND ANAEROBIC (ABSENCE OF OXYGEN) RESPIRATION OR FERMENTATION. Because they operated in the Absence of Oxygen, the products of Glycolysis ENTER the FERMENTATION PATHWAYS are said to be ANAEROBIC PATHWAYS. If OXYGEN is PRESENT, the products of Glycolysis ENTER thePATHWAYS of AEROBIC RESPIRATION. Aerobic Respiration produces a much Larger Amount of ATP, UP TO 20 TIMES MORE ATP PRODUCED.

Stage One: Glycolysis In a series of three reactions, phosphate groups from two ATP molecules are transferred to a glucose molecule. In two reactions, the resulting six-carbon compound is broken down to two three-carbon compounds, each with a phosphate group. Two NADH molecules are produced, and one more phosphate group is transferred to each three-carbon compound. In a series of four reactions, each three-carbon compound is converted to a three-carbon pyruvate, producing four ATP molecules in the process.

Stage Two: Production of ATP When oxygen is present Pyruvate (produced during glycolysis) enters a mitochondria. Pyruvate converted to a two-carbon compound. Reaction produces 1 Carbon dioxide molecule 1 NADH molecule 1 Two-carbon acetyl group. Acetyl group attaches to molecule of coenzyme A (CoA) forming a compound called acetyl-CoA.

Krebs Cycle Named after Hans Krebs, 1937. Steps: Acetyl-CoA combines with a four-carbon compound, forming a six-carbon compound and releasing coenzyme A. Carbon dioxide is released from the six-carbon compound, forming a five-carbon compound. Electrons are transferred to NAD+, making a molecule of NADH. Carbon dioxide released from the five-carbon compound, resulting in a four-carbon compound. One molecule of ATP is made, and one molecule of NADH is produced. Existing four-carbon compound is converted to a new four-carbon compound. Electrons transferred to the electron acceptor, FAD, making a molecule of FADH2, another type of electron carrier. The new four-carbon compound is converted back to the four-carbon compound that began the cycle. Another molecule of NADH is produced.

After Krebs Cycle NADH and FADH2 now contain much of the NRG previously stored in glucose and pyruvate. Four-carbon compound recycled. Acytel-CoA enters the cycle again.

Respiration in the Absence of Oxygen Fermentation – the breakdown of carbohydrates by enzymes, yeasts, or mold in the absence of oxygen. Two types: Lactic Acid Fermentation – 3-carbon pyruvate is converted to a 3-carbon lactate. Lactate – ion of organic acid called lactic acid. When muscles need to function w/o enough oxygen, pyruvate is converted to lactate. Fermentation allows glycolysis to continue to produce ATP. Muscle soreness due to build up of lactic acid in muscle cells. Alcoholic Fermentation – the 3-carbon pyruvate broken down to ethanol (ethyl alcohol), a 2-carbon compound.

Alcoholic Fermentation: Two-step Process. Pyruvate converted to 2-carbon compound, releasing CO2. Electrons transferred from NADH to the 2-carbon compound, producing ethanol. NAD+ recycled, and glycolysis continues to produce ATP. Alcoholic Fermentation by yeasts and fungus used in preparation of foods and beverages: cheese, wine, beer, bread, etc. CO2 produced by yeasts add to carbonation of drinks (i.e. beer) and the rising of bread. See Fig. 16, pg. 110 for ATP production through glycolysis. HW Section 3 Review 1-6, page 110.