Chapter19

Chapter19 - BCH 4054 Chapter 19 Lecture Notes Slide 1...

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Chapter 19, page 1 BCH 4054 Chapter 19 Lecture Notes Slide 1 Chapter 19 Glycolysis Slide 2 Overview of Glycolysis aka The Embden-Meyerhoff Pathway • First pathway discovered • Common to almost all living cells • Occurs in cytoplasm of Eukaryotes • Overall reaction: Glucose + 2 NAD + + 2 ADP + 2 P i 2 Pyruvate + 2 NADH + 2 ATP aka = “also known as” Slide 3 Glycolysis Overview, con’t. • Ten reactions overall • Same in all cells, but relative rates and regulation varies among species and even between tissues (i.e. liver and muscle). • Intermediates all bound to phosphate • Membrane impermeable • Important in energy conversion to ATP • Occurs in two stages (or phases)
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Chapter 19, page 2 Slide 4 Phases of Glycolysis • Phase 1 – Preparatory Phase • Glucose converted to equilibrium mixture of triose phosphates • Investment of 2 ATP’s required • Phase 2 – Energy Yielding Phase • Triose phosphates converted to pyruvate • An oxidation step occurs • Yield of 4 ATP’s, two for each triose phosphate Slide 5 Reactions of Glycolysis (Summary) • Overall Pathway (Figure 19.1) • List of Enzymes (Table 19.1a) • Energetics of Reactions (Table 19.1b) • Intermediate structures, first phase • (Figure 19.2) Slide 6 Phosphorylation of Glucose Energetics: “Driven” by ATP hydrolysis G o ’ kJ/mol glucose + P i glucose-6-P + H 2 O 13.9 ATP + H 2 O ADP + P i -30.5 glucose +ATP glucose-6-P +ADP -16.7 At Q of cell, G can be much larger, -33.9 for erythrocytes, for example (Table 19.1b). The reaction is removed from equilibrium . (Review discussion of phosphate transfer energetics, Table 3.3, pp.67-69) Remember induced fit mechanism, Figure 15.1.
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Chapter 19, page 3 Slide 7 Hexokinase and Glucokinase • Phosphorylation “traps” glucose in the cell. • Figure 19.4 • Transport systems vary. Some cells require insulin. Liver is freely permeable to glucose. • Enzyme in most cells and organisms is hexokinase. Some isozymes exist. Muscle enzyme has Km = 0.1 mM. • Liver has glucokinase, with Km = 10 mM. Hexokinases have a broad specificity as the name implies, phosphorylating a variety of hexoses. They are also inhibited by the product, glucose-6-phosphate, presumably a regulatory function that prevents further phosphorylation if there is no demand for the product. Glucokinase is specific for glucose and is not inhibited by glucose-6- phosphate. The Km of glucokinase is near the normal blood concentration, so that the enzyme becomes more active when blood glucose increases, such as after a meal. Slide 8 Phosphoglucoisomerase • aka glucose phosphate isomerase and hexose phosphate isomerase • Isomerization of an aldose and a ketose . • (We
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This note was uploaded on 05/22/2011 for the course BCH 4054 taught by Professor Logan/gilmer during the Spring '06 term at FSU.

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Chapter19 - BCH 4054 Chapter 19 Lecture Notes Slide 1...

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