PROBLEM SET 7B. Electron Transport and Ox. Phos. (coninued)


This problem set continues with principles electron transport. It focuses on the structure of oxygen and transition metal complexes.

1. Electrons are passed one at a time through the electron transport system to oxygen. Using the MO diagram for oxygen you developed in Problem Set 6, predict the types of molecules that will form when electrons are added to molecular oxugen one at a time.

2. Iron is a transition metal. It has 26 electrons. Two of the eight valance electrons are in the 4s orbital. The remainder are in the 3 d orbitals. Show the orbital distribution of the valance electrons of Fe, Fe+2 and Fe+3.
Hint: The 4s electrons are lost first.

3. Explain how Fe+2 can have coordination numbers of either 4 or 6.

4. Desulforedoxin type proteins, which occur in complex I, and rubredoxin type proteins, which are found in complex II, form transition complexes with either ferrus or ferric ions and four sulfhydryl groups from cysteine residues in the proteins.
a. Show what these complexes look like.
b. What do the roman numerals in FeII and FeIII mean?
c. What are the charges on the ferrus and ferric complexes?
d. Explain how oxidation/reduction can occur without disturbing the coodination complex.

5.Some of the iron-sulfur proteins in the electron transport system are of the general type Fe2S2. They use an inorganic sulfide ion and four sulfhydryl groups of cysteine residues in the protein to form coordination complexes. Show what a typical complex look like.

6. Cytochrome c is an iron porphyrin protein. It uses methionine 80, histidine 18 and the porphyrin ring of protophorphyrin IX to form a transition complex. Disregarding the side chains of protoporphyrin IX, show what the complex looks like.

7. Copper is a transition metal. It has 29 electrons. Eleven are valance electrons. Show the electron distributions of Cu, Cu+ and Cu++.

8. Cytochrome oxidase uses His 181 and 224, Met 221, the carbonyl oxygen of peptide bond Glu 218, CyS 216 and 220 to form a Cu2CyS2 type coordinate complex with either Cu+ or Cu++. Show what the complex looks like. [Hint: HIs181 and Met 221 go together].

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