6 QUESTIONS ALONG WITH THEIR ANSWER THESE QUESTIONS ARE TAKEN FROM 13 AND 14 CHAPTER OF "LEHNINGER PRINCIPLES OF BIOCHEMISTRY" BOOK 6TH EDITION

1. Case study
Presented by:
 Ayesha Kabeer
University of Gujrat Sialkot sub campus

2. Question no. 1
 Once I was sitting in doctor lounge and he was saying his friend who was
quite obese, not to work hard otherwise the fats would come in your blood
and would make you a cardiac patient. I was quite surprised by his advice.
Do you? If yes then please justify the statement.
Answer: The doctor was joking.
Justification on next slide…

4. Question no. 2
• A “pulse-chase“ experiment using 14C-labeled carbon sources is carried out on a yeast
extract maintained under strictly anaerobic conditions to produce ethanol. The
experiment consists of incubating a small amount of 14C-labeled substrate (the pulse)
with the yeast extract just long enough for each intermediate in the fermentation pathway
to become labeled. The label is then “chased” through the pathway by the addition of
excess unlabeled glucose. The chase effectively prevents any further entry of labeled
glucose into the pathway.

5. (a) If [1-14C]glucose (glucose labeled at C-1 with 14C) is used as a substrate, what is the location of 14C in the
product ethanol? Explain.

6. (b) Where would 14C have to be located in the starting glucose to ensure
that all the 14C activity is liberated as 14CO2 during fermentation to
ethanol? Explain
 If all the labeled carbon
from glucose is converted
to 14CO2 during ethanol
fermentation, the original
label must have been on
C-3 and/or C-4 of
glucose, because these
are converted to the
carboxyl group of
pyruvate.

7. Question no. 3
 In working skeletal muscle under anaerobic conditions, glyceraldehyde 3-
phosphate is converted to pyruvate (the payoff phase of glycolysis), and the
pyruvate is reduced to lactate. Write balanced biochemical equations for all
the reactions in this process, with the standard free-energy change for each
reaction. Then write the overall or net equation for the payoff phase of
glycolysis (with lactate as the end product), including the net standard free-
energy change.

8. The pay off phase of glycolysis
 The payoff phase of glycolysis produces ATP, and thus is exergonic. This phase
consists of five reactions, designated 6 to 10:

9. Question no. 4
 Large-scale industrial fermenters generally require constant, vigorous
cooling. Why?
Fermentation releases energy,
some conserved in the form of
ATP but much of it dissipated
as heat. Unless the fermenter
contents are cooled to
counterbalance this heat
production, the temperature
would become high enough to
kill the microorganisms.

10. Question no. 5
 Soy sauce is prepared by fermenting a salted mixture of soybeans
and wheat with several microorganisms, including yeast, over a
period of 8 to 12 months. The resulting sauce (after solids are
removed) is rich in lactate and ethanol. How are these two
compounds produced? To prevent the soy sauce from having a strong
vinegar taste (vinegar is dilute acetic acid), oxygen must be kept out
of the fermentation tank. Why?
Soybeans and wheat contain starch, a polymer of glucose, which is broken down to
glucose by the microorganisms. The glucose is then degraded to pyruvate via
glycolysis. Because the process is carried out in the absence of oxygen (i.e., it is a
fermentation), pyruvate is reduced to lactic acid and ethanol. If oxygen were present,
pyruvate would be oxidized to acetyl-CoA and then to CO2 and H2O. Some of the
acetyl-CoA, however, would also be hydrolyzed to acetic acid (vinegar) in the
presence of oxygen.

12. Question no. 6
 14C-Labeled glyceraldehyde 3-phosphate was added to a yeast extract. After
a short time, fructose 1,6-bisphosphate labeled with 14C at C-3 and C-4 was
isolated. What was the location of the 14C label in the starting
glyceraldehyde 3-phosphate? Where did the second 14C label in fructose 1,6-
bisphosphate come from? Explain.