Question

1. What are the different oxidation states of carbon?

2. How is the hydogen electrode used as the reference half -cell?

3. Which has the higer (more positive) reduction potential, NADH or cytochrome b (Fe³⁺)? In which direction will electrons flow in a system that contains these two compounds?

4. Why is it important to have a universal standard for measuring reduction potentials?

5. Calculate approximately how many molecules of ATP could be synthesized from the complete oxidation of glucose( delta G'^o = -2840 kJ/mol). Revisit this estimate later.

6. what is the significance of the various categories of electron carriers (water-soluble vs. lipid-soluble; mobile vs. bound; associated with peripheral vs. integral membrane proteins) in terms of an electron carrier's functions?

7. How do the normal concentration ratios of NAD⁺/NADH and NADP⁺/NADPH in cells reflect the different metabolic roles of these electron carriers?

Answer 1

1.

Carbon forms an extensive number of compounds due to its catenation property.

Its oxidation state may vary from +4 to -4 in the compounds.

Remember, it is a formal charge as most of the carbon compounds are covalent in nature.

2.

A standard hydrogen electrode is used as the reference electrode for all the metals.

Its reduction potential is set to zero.

It is formed by bubbling hydrogen gas at 25C and 1 atm through an inert electrode.

Half reaction:

2H+ + 2e- -----> H2

3.

A positive reduction potential means that the given compound has a higher affinity for electrons compared to hydrogen.

NADH is a strong electron donor.

Redox potential of NADH = -.032 V

Redox potential of Cyt b3 = +0.22 V

So, electrons flow from NADH to Cyt b3.

4.

It is important to have a standard to compare the reduction potentials of two different compounds.

Generally, H2 is used as the standard whose redox potential is set to zero.

Electrons flow to high positive redox potential from low positive/negative redox potential.

Flow of electrons:

Glucose ---> NADH ---> GSH ---> Cyt b ---> Cyt c ---> Cyt a ---> Fe+2