Cell Structure and Function                                           Name: ________________________

Fall, 2001                                                                     Collaborators: __________________

Homework 1

Due: Wednesday Sept. 19.

 

 

  1. After graduation you have taken a job with a major biochemical company.  During the first week on the job your supervisor notices that you need to brush up on some of the basics of enzyme kinetics.  To bring you up to speed she arranges for you to do an experiment at a local zoo.  When you arrive you discover that you have been assigned to a troop of 10 monkeys trained to shell peanuts.  The monkeys have been herded into a side room next to a large “peanut gallery” where peanuts have been placed on the floor at a concentration of 1 peanut/square meter.  The monkeys are let into the room where they immediately begin to pick up and shell the peanuts.  You follow this process closely and record the following data:

 

 

            Peanut concentration (per meter squared)                                              1

           

            Time required per peanut 

                        To find (sec/peanut):                                                                 9

                        To shell (sec/peanut):                                                                1

                        Total (sec/peanut):                                                                    10

 

            Rate of shelling  

                        Per monkey (peanut/sec)                                                          0.1

                        Total for 10 monkeys (peanut/sec)                                            1

 

Your supervisor is pleased with your attention to detail and suggests that you try another assay at a higher peanut concentration.  So, you herd the monkeys back into the waiting room, triple the peanut concentration, release the monkeys, and record the same parameters:

 

            Peanut concentration (per meter squared)                                              3

           

            Time required per peanut 

                        To find (sec/peanut):                                                                 3

                        To shell (sec/peanut):                                                                1

                        Total (sec/peanut):                                                                    4

 

            Rate of shelling  

                        Per monkey (peanut/sec)                                                          0.25

                        Total for 10 monkeys (peanut/sec)                                            2.5

 

 

To determine if you understand the relationship of this “experiment” to enzyme kinetics, your supervisor asks you to indicate which of the parameters you measured represents:

 

            Substrate concentration, [S] _________________________  (1 point)

            Rate or velocity of the reaction, v _____________________ (1 point)

 

Given the information above your supervisor points out that you can predict the outcome of addition experiments using different peanut concentrations.  Try a few concentrations and make a graph of kinetics (like that discussed in class) in which you plot v on the y-axis (suggested scale: 1-10) and [S] on the x-axis (suggested scale: 0-100).  After completing this exercise use the data to give an estimate of:

 

            vmax _______________________________ (5 points)

            km ________________________________  (5 points)

 

 

  1. Cell biologists often use drugs as inhibitors to study how a particular process works.  Two such compounds used to determine the mechanism of ATP production in mitochondria are oligomycin and sodium azide.

 

Shown below are results obtained by incubating isolated, intact mitochondria in phosphate-buffered saline containing pyruvate, ADP, Pi, and O2.  The control was mitochondria with no drug added. 

 

                                      Control                       Oligomycin                   Sodium azide

ATP produced                 yes                                  no                                  no

O2 consumed                    yes                                  yes                                 no          

CO2 produced                  yes                                  yes                                yes          

NADH produced             yes                                  yes                                yes          

Proton gradient formed   yes                                    yes                                 no

 

Based on your specific knowledge of the structure and function of mitochondria and your analysis of these data what specific part of the energy-generating machinery of mitochondria is inhibited by:

 

a.       oligomycin __________________________ (4 points)

b.      sodium azide _________________________ (4 points)