In silence contemplate the dynamics of dry ice in water.

During the first minute, allow your mind to go where it wants.

The 2002 winter Olympics have just ended which means it is time to start training for the 2006 Olympics in Torino, Italy.

Find a place on the wall, and position yourself as if you were sitting on a chair with your thighs parallel to the floor. Hold this position for 60 seconds. Assign a rating to your comfort level (1= "I could hold a 50 pound weight comfortably in my lap" and 10 = "All I see is a white light")

During exercise your muscles get the energy needed contract and relax from the conversion of adenosine triphosphate (ATP) to adenosine diphosphate (ADP):

ATP g ADP + Energy

Most of the ATP is made by burning (oxidizing) glucose to form ATP and lactic acid (a waste product). In the presence of oxygen, the final products are carbon dioxide and water:

Glucose + ADP g lactic acid + ATP

Lactic acid + O₂ g CO₂ + H₂O

1. Write down the lactic acid (CH₃CHOCOO-H) equilibrium in water:

CH₃CHOCOO-H + H₂O <---> CH₃CHOCOO^- + H₃O⁺

2. What physiological response removes the products during exercise?

3. From your knowledge about acids and bases, describe what happened to the pH in your muscles in the final seconds of the wall sit. (Hint: Energy conversion went from aerobic (with oxygen) to anaerobic (without oxygen)). What causes the "burn?"

The lactic acid is transported to other areas in your body where oxygen is available in your blood stream. Dramatic changes in the pH of your blood must be buffered (compensated for) or you will die.

The buffer system in the blood is based on the carbon-containing product of respiration.

4. What is the carbon product of respiration? CO₂

5. Write the relevant equilibria of the buffer system in blood.

CO₂ + H₂O <==> H₂CO₃

H₂CO₃ + H₂O <==> HCO₃^- (Buffer)

6.The titration plot is for Na₂CO₃. Before proceeding, make sure you can identify what carbonate species predominate in the regions of the titration plot and label the plot if you like.

The attached Graph 18 shows how the concentration of lactic acid in the blood changes with how hard three different people are working. Look at the middle curve for the amateur. There is a region where the concentration of lactic acid in the blood increases slowly then jumps dramatically. If you reached about a 7 during the wall sit you probably hit this region of the graph.

7. Write an equation to show how the blood buffer system neutralizes the acid produced during exercise.

Or

HCO₃^- + CH₃CHOCOO-H <==> CH₃CHOCOO^- + H₂CO₃

8. Look at the blood buffer (carbonate) titration curve. Identify (circle) the region of the plot that corresponds to the slow increase in lactic acid observed in Graph 18 for the amateur. Next, circle the region of the titration plot that corresponds to the sudden, sharp increase in lactic acid concentration that crosses the anaerobic threshold (and causes pain!) in the amateur.

9. There is a very useful formula (biochemists use it a lot) to easily calculate the pH of a buffer solution.

pH = pKa + log( [A-] / [HA] )

where HA is the acid form ( i.e., protonated) of the buffer

and A- is the conjugate base form (i.e., deprotonated).

In blood, [HCO₃^-] = 0.015M. The [H₂CO₃] depends on the amount of CO₂ dissolved in the blood:

CO₂(aq) + H₂O <=> H₂CO₃ K = 0.0031

(a) Calculate the [H₂CO₃] if the concentration of dissolved gas, [CO₂(aq)] = 0.0012M

K = [H₂CO₃]/ [CO₂]

(b) Now, what is the pH of the blood buffer system? K_a = 0.000148

pH = pKa + log([HCO₃^-] / [H₂CO₃] )

1O. What seems to be an incredibly important equilibria system on earth? (Which system have you studied today for the third time this semester?) Carbonic acid/CO₂