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1.8 ${\displaystyle E_{cell}=E_{cell}^{\circ }-{\frac {RT}{nF}}\ln(Q)}$

1.9

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Topics/Subtopics for Assignment

• Iron-Sulfur Clusters - there is little information of the topic of Iron-Sulfur Clusters, I aim to find more information and add/expand on the article
  • Find specific enzymes/proteins that contain Iron-Sulfur clusters
  • Add internal Wikilinks to other wiki articles for related topics
  • Explore possible biochemical processes
  • Find/Create new figures that show different structure or interactions with other compounds/systems

Article providing info on structure, function, formation of Fe-S Clusters

Article Title: Structure, Function, and Formation of Biological Iron-Sulfur Clusters

Subtopic: Occurrences of Iron-Sulfur Clusters In Biology

Notes (Not To Be Marked):

• Have ability to delocalize electron density over Fe and S atoms, ideal for electron transport^[1]
• Major components in photosynthetic, respiratory electron transport chains, e- transport pathways of membrane bound enzymes, and redox-active centers in ferredoxins^[1]
• Found in Rubredoxin (electron transfer protein) (textbook)^[2]
• Found in the cytochrome bc1 complex III of electron transfer chain of animals
• Found in Cytochrome b6f complex of photosynthetic electron transfer chains in plants, cyanobacteria, and green algae
• Redox inactive 4Fe-4S clusters have structural roles in DNA repair enzymes^[1][3]

Occurrences of Iron-Sulfur Clusters in Biology (250 Word Contribution) (REVISED)

Iron-Sulfur clusters occur in many biological systems as part of electron transfer proteins and enzymes due to their ability to aid in the transport of electrons over large distances. This property of the Fe-S clusters plays a crucial role in the proteins as they are used for the transportation of electrons in many biological processes.^[1]

The Rieske proteins contain Fe-S clusters that coordinate as a 2Fe-2S structure and can be found in the membrane bound cytochrome bc1 complex III in the mitochondria of animals and bacteria (eukaryotic cells). They are also a part of the proteins of the chloroplast such as the cytochrome b₆f complex in photosynthetic organisms. These photosynthetic organisms include plants, cyanobacteria, and green algae (prokaryotic cells). Both are part of the electron transport chain of their respective organisms which is a crucial step in the energy harvesting for many organisms.^[2]

High potential iron-sulfur proteins occur in photosynthetic anaerobic bacteria and contain Fe-S clusters that coordinate in a 4Fe-4S cuboidal structure within the protein. ^[2]

The ferredoxin protein is a protein that contain within it either a coordinated 2Fe-2S cluster or a coordinated 4Fe-4S cuboidal cluster. The ferredoxin proteins that have the 2Fe-2S cluster can be found naturally occurring in a wide variety of eukaryotic cells whereas the ones containing the 4Fe-4S coordinated clusters usually only occur in bacteria.^[2]

There have also been some instances where proteins contain redox-inactive 4Fe-4S clusters and are proposed to have structural roles. Such enzymes as endonuclease III and MutY, which are important for repair of damaged DNA in many organisms, are said to contain these redox-inactive clusters that do not act toward catalytic properties but contribute to structure and positioning of the enzyme.^[1][3]

https://commons.wikimedia.org/wiki/File:Photosystem_1_-_Crystal_Structure.png https://commons.wikimedia.org/wiki/File:Ferredoxin_4Fe-4S_Metal_Center_Coordination.png

https://commons.wikimedia.org/wiki/File:Rubredoxin_from_Pyrococcus_Furiosus.png

https://commons.wikimedia.org/wiki/File:Rieske_Protein_from_Cytochrome_BC1-Complex.png

https://commons.wikimedia.org/wiki/File:HiPIP_(Fe4S4)2%2B.png

Iron-Sulfur Proteins - Second 250 Word Contribution

Covalency of Iron-Sulfur Proteins (New Addition to Article)

Experimental data shows that iron ions and sulfur ions have a tendency to form stable metal-ligand coordination bonds and have higher covalency. Being that Fe2+/3+ are considered a hard metal ion and a sulfur ion is considered a soft ligand one would not assume that the two ions would coordinate very well. When a molecule with a sulfur group coordinates to Fe2+/3+ ion, they have a high effective nuclear charge that increases the covalency of the iron sulfur bond. Data collected using X-ray Absorption Spectroscopy (XAS) shows that the covalency of an iron metal complex is greater when the metal is coordinated to sulfur ion as opposed to a chloride ion for both 2Fe-2S and 4Fe-4S complexes.^[3] (Lecture e- transfer P2a)

Structural Motifs (Adding to Addition Information)

The protein backbone provides a rigid structure that holds the iron and sulfur atoms at certain bond distances and bond angle that closely resemble some model complexes however, small differences in geometry help enforce an entatic state.^[3]

4Fe-4S Clusters (Re-wording and Adding Additional Info to Article)

The most stable form of the 4Fe-4S cluster contained within bacterial ferredoxin and HiPIP occur when the iron ions in the cluster are have two iron atoms in the 2+ oxidation state and two iron atoms in the 3+ oxidation state. In this state one electron is delocalized between the two mixed valence pair Fe2+ and Fe3+ ions making the resulting metal ions exist in an Fe2.5+ oxidation state.

For the bacterial ferredoxin, the [2Fe2+, 2Fe3+] cluster exists as the oxidized form and is reduced when an electron is added to one of the Fe3+ ions.

For the HiPIP, the [2Fe2+, 2Fe3+] cluster exists as the reduced form and is oxidized when an electron is removed from one of the Fe3+ ions.^[3]