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

2 Respiration involves three stages: Glycolysis تحلل الجلوكوز harvests تحصد chemical energy الطاقة الكيميائية by oxidizing glucose to pyruvate ()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 ) 3.Electron transport نقل الاليكترونات chain to synthesisATP ( 3.Electron transport نقل الاليكترونات chain to synthesis ATP ( inner mitochondrial membrane ). Cellular respiration generates ينتج many ATP molecules. For each sugar molecule جزيء سكر () Cellular respiration generates ينتج many ATP molecules. For each sugar molecule جزيء سكر ( 38 ATP molecule )

3 1.glucose () is 1.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). 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. 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. 1- Glycolysis ( splitting glucose ): harvests chemical energy by oxidizing glucose to 2-pyruvate حصاد الطاقة الكيميائية عن طريق اكسدة الجلوكوز الى بيروفات Fig. 9.8

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

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

7 Pre Krebs cycle

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