BCH 4054                        HOUR TEST 1          NAME _____________________
 September 27, 1995

Points

(25) 1.   The liver oxidizes fatty acids primarily to
          acetoacetate which then serves as fuel for
          peripheral tissues.  Sketch a pathway by which
          the liver would convert the five-carbon fatty
          acid pentanoic acid (CH3CH2CH2CH2COOH) to
          acetoacetate according to the following overall
          reaction:

          CH3CH2CH2CH2COOH  --->  CH3COCH2COOH + CO2

          Show all the intermediates in the pathway and identify the steps
          producing CoQH2, NADH, and using or producing ATP and GTP.  Based on
          the stoichiometry of oxidative phosphorylation we discussed in class,
          calculate the total net yield of ATP in this process.



























(12) 2.   The alanine cycle is similar to the Cori cycle, except that alanine
          instead of lactate is transported from muscle to liver for further
          metabolism.  In addition to providing fuel for synthesis of more
          glucose in muscle, alanine also serves as a carrier of nitrogen from
          muscle to liver in times of muscle protein degradation.  The
          following conversion must occur in liver:

               alanine  --->  pyruvate  +  NH3  

          Give the reaction steps accomplishing this conversion, including the
          name of the enzyme catalyzing each step, the structure of the
          reactants and products of each step, and the name of any coenzyme
          cosubstrates or coenzyme prosthetic groups involved.  


















(12) 3.   Two steps of the urea cycle require ATP.  Identify them by giving the
          structures of the reactants and products (abbreviations for coenzyme
          cosubstrates are okay) and the name of the enzyme catalyzing each
          step.


     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     4.   Mitochondria that are poisoned by cyanide can still carry out the
          following reaction:

          NADH  +  2 cyt c(ox)  ---->   NAD+  +  2 cyt c(red)

            Given:  Eo' for NAD+/NADH = -0.32 volts  
                    Eo' for cyt c(ox)/cyt c(red) = +0.25
                    R=8.3 x 10-3 kJ mol-1 K-1, T=25oC, F=96.5 kJ V-1 mol-1

(6)       (a)  Calculate delta Go' for this reaction.







(7)       (b)  Circle the intermediate electron carriers in the following list
               that would be involved in this overall reaction, and then place
               them in the proper order in which they function in the electron
               transfer.

               cyt a,     cyt a3,   cyt b,    cyt c1,    FAD,      FMN, 

               Fe/S protein,        Cu,       phycocyanin,         succinate





(6)       (c)  Calculate the proton motive force (delta p) that can be generated by
               this reaction if the reaction were coupled to the transport of:

               (1)  two protons



               (2)  four protons



               (3)  six protons




(6)       (d)  delta Go' for ATP synthesis is + 30 kJ mol-1.  Best current estimates
               are that the above reaction would yield the coupled synthesis of
               1.5 moles of ATP.  Calculate the overall delta Go' for the coupled
               reaction, and give a rationalization for the 1.5 mole
               stoichiometry.
















(15) 5.   In the Z scheme for the light reaction of photosynthesis two pigment
          systems are responsible for the transfer of electrons from water
          (forming oxygen) to NADP+ (forming NADPH).  Outline the scheme,
          placing the following components in their proper location along the
          path of the electrons:  plastoquinone, plastocyanin, manganese,
          ferredoxin, cytochrome b/f complex, P700, P680, pheophytin.






















(6)  6.   Match a component in the list at the right with each statement below
          by placing the appropriate letter in the blank.  

     ___  reduced directly by P680*.          a.  pheophytin a
                                              b.  plastocyanin
     ___  oxidized directly by P680+.         c.  phycocyanin
                                              d.  a tyrosine residue
     ___  oxidized directly by P700+.         e.  Ao, a chlorophyll a

     ___  reduced directly by P700*.

     ___  an accessory pigment.

     ___  chlorophyll a without Mg2+.


(5)  7.   Explain how cyclic photophosphorylation differs from the reaction
          described by the Z scheme in question 5 above.  The overall products
          of the Z scheme are O2, NADPH, and ATP.  What are the overall
          products of cyclic photophosphorylation?