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cellular respiration review

cellular respiration review - Bio 211 Intro Molecular and...

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Bio 211 Intro Molecular and Cell Biology Lecture 14 "Krebs Cycle" Reading: Campbell Chap. 9 pp. 156-166 Homework: Write out sequence of steps in glycolysis for class In the last lecture, we introduced you to some of the processes of energy metabolism. Today we will look at two of these processes in some depth, glycolysis and the Krebs cycle. In these pathways, glucose is broken down into pyruvate, then further into carbon dioxide and water. If you have your homework with you, please have at hand for the first part of today’s class. Outline: 1. Glycolysis (full pathway) 2. Fermentation 3. Krebs cycle 1. Glycolysis: In the first part of the period today, we will review the process of glycolysis. Let’s try to summarize some of the key features of glycolysis . a. What is the starting material? Glucose b. Where does glycolysis occur? Cytosol c. What is glucose broken down into? 2 Pyruvate d. What are the other products formed from glycolysis? ATP and NADH + H + e. What is meant by the energy-requiring and energy pay-off phases? In the first phase ATP is used up, in the second phase ATP is produced. f. What is substrate-level phosphorylation? Production of ATP from ADP by transfer of a phosphate from a glycolytic intermediate. g. What happens next to the pyruvate? In the presence of oxygen, it is oxidized further and enters the Krebs cycle. h. What happens next to the NADH? In the presence of oxygen, it passes its electrons to the electron transport chain, ultimately yielding additional ATP. Remember that the end result of glycolysis is: Glucose ----> 2 Pyruvate + 2 H 2 O 2 ADP + 2 P i ----> 2 ATP 2 NAD + ----> 2 NADH + H + 1
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Using Fig. 9.9 or your homework notes, we will next take a closer look at glycolysis. On the exam, you won’t need to know all the details such as all of the chemical structures and the names of the enzymes. However, I do want you take at least one look at what’s really happening. Step 1: Glucose + ATP ----> glucose-6-phosphate + ADP Glucose enters the cell and is phosphorylated by the enzyme hexokinase, which transfers a phosphate group from ATP to the sugar. You may remember that I used this example in the lecture on thermodynamics. Adding phosphate to glucose is an energetically unfavorable reaction. By coupling the breakdown of ATP to the phosphorylation of glucose, the reaction now becomes energetically favorable. Step 2: glucose-6-phosphate ----> fructose-6-phosphate In this reaction catalyzed by an isomerase , one sugar is converted into its isomer.
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