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Chapter18 - BCH 4054Chapter 18 Lecture Notes Slide 1...

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Chapter 18, page 1 BCH 4054—Chapter 18 Lecture Notes Slide 1 Chapter 18 Metabolism Overview Slide 2 Metabolism Metabolism is the sum of all the chemical changes occurring in the cell. Nutrients fi Cellular 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 Links Slide 3 Stages of Metabolism Proteins Nucleic Polysaccharides Lipids Acids I Amino Purines, Sugars Fatty Acids Pyrimidines Acids, pentose Sterols II III Simple Molecules CO 2 , NH 3 Cata bolism: Degradative, Exergonic, Oxidative Anabolism: Synthetic, Endergonic, Reductive Some reactions can be either catabolic or anabolic, depending on the circumstances. Such reactions are called amphibolic reactions. 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. Linear 2. Branched 3. Cyclic 4. Equilibrium pool Linear 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 F 2. Branched Pathway: A B X Y Z C D E Q R S A B C Q R S X Y M N O or Branched 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. A B C D E X Z 3. Cyclic Pathway In 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.
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