CHAPTER 9 CELLULAR RESPIRATION: HARVESTING CHEMICAL ENERGY

1. CHAPTER 9CELLULAR RESPIRATION: HARVESTING CHEMICAL ENERGY Section B: The Process of Cellular Respiration

2. Section B: The Process of Cellular Respiration • Respiration involves three stages: • Glycolysis تحلل الجلوكوز harvests تحصد chemical energy الطاقة الكيميائية by oxidizing glucose to pyruvate (in cytoplasm) • 2.Krebs cycle دورة كريبس completes the energy-yielding معطي للطاقة oxidation of organic molecules as it It degrades تحلل pyruvate to carbon dioxide. • (in mitochondrial matrix) • Electron transport نقل الاليكترونات chain to synthesisATP (inner mitochondrial membrane). • Cellular respiration generates ينتج many ATP molecules. For each sugar molecule جزيء سكر (38 ATP molecule)

3. 1- Glycolysis (splitting glucose): harvests chemical energy by oxidizing glucose to 2-pyruvateحصاد الطاقة الكيميائية عن طريق اكسدة الجلوكوز الى بيروفات • glucose (a six carbon-sugar سكر سداسي الكربون) is split يتكسر into two molecules of pyruvate. (each is three-carbon sugar سكر ثلاثي الكربون ). 2. These steps can be divided into two phases: A)- Energy investment phase:استهلاك طاقة ATP is consumed يستهلك to provide activation energy by phosphorylation of اضافة الفوسفات glucose (this requires 2 ATP per لكل glucose). B)- Energy payoff phase:إنتاج طاقة 4ATP are produced by reduction اختزال of NAD+ to NADH. 3. Thus, the net yield الناتج النهائي from glycolysis is 2 ATP and 2 NADH per glucose. Fig. 9.8

5. 2. The Krebs cycle completes the energy-yielding oxidation of organic molecules (in mitochondrial matrix): It includes two cycles : Pre-Krebs cycle المرحلة التحضيرية Krebs cycle

6. Fig. 9.10, Page 164 2 NAD+ 2Acetyle-CoA 2Pyruvate CoA Krebs Cycle A)- Pre-Krebs cycle Pyruvate is converted تتحول into acetyle-CoA in the presenceفي وجود of O2 through 3 stepsفيثلاثخطوات a)- C=O- group of pyruvate is released as CO2. b)- The remaining two-C fragments are oxidized (releasing e-) intoacetate and the resulting e- transform NAD+ into NADH. c)- The coenzyme-A (CoA) transform acetate compound into acetyle-CoA, which enter يدخل Krebs Cycle for oxidation. 2 NADH+H+ + CO2 + H2O

7. Fig. 9.10, Page 164

8. Pre-Krebs Cycle Output Flavin Adenine Dinucleotide B)- Krebs cycle It has eight steps starting with 2 acetyle-CoA compunds. They are summarized as in Fig. 9.12: • This cycle begins when acetate from each acetyl-CoA combines with oxaloacetate (4 C atoms) to form citrate (citric acid). • Ultimately, the oxaloacetate is recycled and the acetate is broken down to CO2. • Each cycle produces one ATP, three NADH, and one FADH2 (another electron carrier) per acetyl CoA. Thus, the outcome of the two cycles is (for the 2 Acetyle-CoA molecules): 2 ATP 6 NADH 2 FADH2 Fig. 9.12, Page 166