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CHEM203: Bioinorganic Chemistry

Unit 4: Electron Transfer in Biological Systems   Electrons are continuously supplied and removed during the course of biological processes.  Because transition metals can take on multiple oxidation states, they are particularly suitable for these electron-transfer tasks.  The most common metal centers for electron-transfer reactions are based on copper and iron cations.  Metal ions also play an essential role in photosynthesis and other processes in plant and algal systems.  In this unit, you will learn about the role and importance of metal ions that are involved in the electron traffic of biological systems – including, in particular, those that are crucial to the processes of plant and algal systems.

Unit 4 Time Advisory
This unit should take you approximately 18 hours to complete.

☐    Subunit 4.1: 6 hours   

☐    Subunit 4.2: 2 hours   

☐    Subunit 4.3: 10 hours

Unit4 Learning Outcomes
Upon successful completion of this unit, the student should be able to: - Explain electron-transfer kinetics and long-range electron-transfer mechanisms. - Discuss the importance of the protein control of redox potentials. - Describe the most common copper- and iron-based electron-transfer systems. - Discuss the importance of inorganic compounds in energy capture and synthesis in plant-based systems, specifically during the process of photosynthesis.

4.1 Electron-Transfer Kinetics and the Marcus Theory of Electron Transfer   - Reading: Bioinorganic Chemistry: Dr. Harry B. Gray and Dr. Walther R. Ellis, Jr.’s “Chapter 6: Electron Transfer” Link: Bioinorganic Chemistry: Dr. Harry B. Gray and Dr. Walther R. Ellis, Jr.’s “Chapter 6: Electron Transfer” (PDF)
 
Instructions: Please click on the link above to access the online textbook.  Then, scroll down the webpage and click on the link for chapter 6 to open a PDF version of the chapter, which you should read in its entirety.  You may also choose to download the PDF for the entire book and navigate to chapter 6, which begins on page 315.
 
As you read, keep in mind that, in biological systems,oxidation refers to the addition of oxygen bonds or the removal of hydrogen, while reduction refers to a decrease in the number of bonds to oxygen or an increase in hydrogen.  Also consider the structural effects of biological molecules in terms of long-range and short-range electron transfer.  Note that this chapter also discusses the Marcus theory of electron transfer, beginning in section III, on page 336.  Marcus theory helps explain the probability of outer-sphere (long-range) and inner-sphere (short-range) electron transfer.
 
Please note that this reading also covers material you need to know for subunit 4.2, found below.  When you reach that subunit, you may find it helpful to refer back to this material for review.
 
This reading, including note-taking, should take you approximately 6 hours to complete.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

4.2 Photosynthesis   Note: Some of the material you need to know for this subunit is covered in the textbook reading assigned beneath subunit 4.1, found above.  You may find it helpful to refer back to that material as you complete the reading below; in particular, focus on the discussion of photosynthesis that occurs on pages 327-330 of the textbook.

  • Reading: The College of Saint Benedict/St. John’s University: Dr. Henry Jakubowski’s Lecture Notes: “Chapter 8 – Oxidation/Phosphorylation” Link: The College of Saint Benedict/St. John’s University: Dr. Henry Jakubowski’s Lecture Notes: “Chapter 8 – Oxidation/Phosphorylation” (HTML)
     
    Instructions: Please click on the link above to access and read the entire webpage.  This material covers the mechanisms of photosynthesis I and II.  Spend some time looking over the illustrated models throughout the text.  These models allow you to visualize light-harvesting molecules, as well as their protein structures and internal hydrogen bonding.
     
    This reading should take you approximately 2 hours to complete.
     
    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

4.3 Bio-Redox Agents and Electron-Transfer Mechanisms   - Reading: Bioinorganic Chemistry: Dr. Edward I. Stiefel and Dr. Graham N. George’s “Chapter 7: Ferredoxins, Hydrogenases, and Nitrogenases: Metal-Sulfide Proteins” Link: Bioinorganic Chemistry: Dr. Edward I. Stiefel and Dr. Graham N. George’s “Chapter 7: Ferredoxins, Hydrogenases, and Nitrogenases: Metal-Sulfide Proteins” (PDF)
 
Instructions: Please click on the link above to access the online textbook.  Then, scroll down the webpage and click on the link for chapter 7 to open a PDF version of the chapter, which you should read in its entirety.  You may also choose to download the PDF for the entire book and navigate to chapter 7, which begins on page 365. This reading deals with iron-based electron-transfer mechanisms.  Ferredoxins refer to iron-sulfur clusters; hydrogenases utilize other metals, specifically nickel, with iron; and nitrogenase is an iron-based enzyme used in nitrogen fixation. 
 
Please note that this reading also covers the material you need to know for sub-subunits 4.3.1-4.3.4, found below.  When you reach those sub-subunits, you may find it helpful to refer back to this reading for a review of specific topics.
 
This reading, including note-taking, should take you approximately 8 hours to complete.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

4.3.1 Iron-Sulfur-Cluster Electron-Transfer Sites   Note: The material you need to know for this sub-subunit is covered in the textbook reading assigned beneath subunit 4.3, found above.  Information pertaining specifically to iron-sulfer-cluster electron-transfer sites can be found in section I, on pages 365-400 of the textbook.  Spend approximately 45 minutes reviewing this material before moving on to the next sub-subunit of this course.

4.3.2 Iron Hydrogenases   Note: The material you need to know for this sub-subunit is covered in the textbook reading assigned beneath subunit 4.3, found above.  Information pertaining specifically to iron hydrogenases can be found in section II.B.3, on pages 405-409 of the textbook.  (Pages 401-405 cover hydrogenases in general.)  Spend approximately 15 minutes reviewing this material before moving on to the next sub-subunit of this course.

4.3.3 Nickel-Iron Hydrogenases   Note: The material you need to know for this sub-subunit is covered in the textbook reading assigned beneath subunit 4.3, found above.  Information pertaining specifically to nickel-iron hydrogenases can be found in section II.B.4, on pages 409-411 of the textbook.  Spend approximately 15 minutes reviewing this material before moving on to the next sub-subunit of this course.

4.3.4 Nitrogenases   Note: The material you need to know for this sub-subunit is covered in the textbook reading assigned beneath subunit 4.3, found above.  Information pertaining specifically to nitrogenases can be found on pages 412-444.  Spend approximately 45 minutes reviewing this material before moving on to the next unit of this course.