This question relates to The role of metal-containing proteins in biological processes and Molecular orbital theory of transition-metal complexes sections. a) Nitro genases catalyse the reduction of dinitrogen to ammoniain bacteria. These enzymes are comprised of a complex oftwo proteins, with the Fe-protein transferring electrons to the FeMo protein, where dinitrogen reduction occurs. The precise mechanism for the reduction of dinitrogen is still poorly understood so the behaviour of other small molecule or ion substrates, such as CO and CN- have been studied to improve understanding. i. The protein consists of four polypeptide chains, with each chain marked by a different colour (when the polymer is shown as a cartoon, as it should be when you enter the page). Take a screen grab of the protein and state which chain corresponds to which colour. You can identify the chains by hovering over them. You may need to rotate the structure to identify all the chains.(2 marks) ii. On the tab on the right-hand side of the page titled"Structure", remove the polymer atoms (the polypeptidechain) from the view by clicking on the dustbin symbol adjacent to the polymer option. Then, screen grab the image and upload to your answer. iii. The structure contains two pairs of clusters. By referring to the information given in the Visualising molecules and proteins document, measure the distance between the metal-sulfur clusters in either of these pairs. Note, you will lneed to select the "Residue" option, rather than the"Atom/coarse element" option described in the visualisation document, from the Residue drop-down menu. This is because the clusters are classed as residues in the PDB. iv. Examine, the metal-sulfur clusters in the protein. Describe how each pair of clusters meets the criteria for a good electron transport system. v. For one of the pair of metal-sulfur clusters, identify whichis the cluster is the P-cluster and which is the FeMo-cofactor and upload an annotated screengrab whichshows your choice. vi. Based on your knowledge of nitrogenases, which of the P-cluster or the FeMo-cofactor would you expect to have thelower electrode potential? Explain your answer. vii. One of the clusters in each pair has CO bound to it.Describe coordination mode of the CO including a sketch of how the CO interacts with the metal atoms (you don't need to include the whole cluster in your sketch).

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