Chapter 18, page 1 BCH 4054—Chapter 18 Lecture Notes Slide 1 Chapter 18Metabolism OverviewSlide 2 Metabolism•Metabolism is the sum of all the chemical changes occurring in the cell.Nutrients fiCellular Constituents, Energy•Metabolic Maps summarize the intermediates of metabolism, and the reactions connecting them.•See Figure 18.1 •Explore the Boehringer-Mannheim maps under External LinksSlide 3 Stages of MetabolismProteins Nucleic Polysaccharides LipidsAcidsIAmino Purines, Sugars FattyAcids Pyrimidines Acids,pentose SterolsIIIIISimpleMolecules CO2, NH3Cata bolism: Degradative, Exergonic, OxidativeAnabolism: Synthetic, Endergonic, ReductiveSome reactions can be either catabolic or anabolic, depending on the circumstances. Such reactions are called amphibolicreactions. Many of the reactions interconverting the “simple molecules” fall in this category. Catabolic and anabolic pathways are interrelated in three ways: Matter (catabolic pathways furnish the precursor compounds for anabolism0 Energy (catabolic pathways furnish the energy to “drive” anabolism) Electrons (catabolic pathways furnish the reducing power for anabolism)
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Chapter 18, page 2 Slide 4 Topology of Metabolic Pathways•There are four ways that pathways can be organized “topologically”1.Linear2.Branched3.Cyclic4.Equilibrium poolLinear pathways convert one compound through a series of intermediates to another compound. An example would be glycolysis, where glucose is converted to pyruvate. Slide 5 Pathway Topology, con’t.1. Linear Pathway:A B C D E F2. Branched Pathway:A B X Y ZC D EQ R SA B CQ R S X YM N OorBranched pathways may either be divergent (an intermediate can enter several linear pathways to different end products) or convergent (several precursors can give rise to a common intermediate). Biosynthesis of purines and of some amino acids are examples of divergent pathways. There is usually some regulation at the branch point. The conversion of various carbohydrates into the glycolytic pathway would be an example of convergent pathways. Slide 6 Pathway Topology, con’t.ABCDEXZ3. Cyclic PathwayIn a cyclic pathway, intermediates are regenerated, and so some intermediates act in a catalytic fashion. In this illustration, the cyclic pathway carries out the net conversion of X to Z. The Tricarboxylic Acid Cycle is an example of a cyclic pathway.