STUDY GUIDE
Metabolism and Biochemistry
These practice problems will help you get a better understanding of how
glycolysis, the Krebs/Citric Acid Cycle, and the Electron Transport Chain
(oxidative phosphorylation) produce ATP for the cell. These problems are
optional, but will help you understand the fundamental ideas behind
metabolism!
How to best use this set:
i: First, try to solve the problems from memory.
ii: If that fails, consult your textbook and lecture notes. Internet sources may also
help, but it's best not to just look up the answer. Note down whatever facts seem
relevant, and re-examine the question again.
iii: If that fails, talk to other students or me.
iv: If that fails, check the answer key.
1. Name three proteins that require ATP in order to function properly and their
roles in the cell. You may need to search through your text to find examples.
2. a) What is the difference between the change in free energy associated with a
reaction and the heat release (enthalpy change) associated with a reaction?
b) Which of those values directly tells us whether or not a reaction is
spontaneous?
3. a) Give an example of a reaction that is spontaneous, yet would proceed slowly
at room temperature if there were no catalysts present.
b) What do we call proteins that cells use as catalysts to speed up chemical
reactions?
4. a) Are all of the steps of glycolysis spontaneous? If not, name one nonspontaneous step.
b) Is the entire process of glycolysis spontaneous as a whole? Why or why not?
5. a) How much free energy is released (per molecule or per mole, your choice),
when converting ATP into ADP and phosphate? You may need to look online to
find this.
b) Assuming that our metabolism can produce 38 moles or molecules of ATP
(some books say 36) out of every mole/molecule of glucose, estimate how much
energy we harvest from each mole/molecule of glucose. (Use your result from
part a).
c) How much free energy is released, in theory, when you light glucose on fire,
converting it into carbon dioxide and water? (You will need to look up the delta G
for glucose combustion online. Do NOT use the enthalpy change!)
STUDY GUIDE
Metabolism and Biochemistry
d) What percentage of the available free energy of combustion in sugar (answer to
c) is actually used to make ATP (answer to b)? Given that the rest of this energy is
lost as waste heat (or used to heat the body), this will tell you the efficiency of
energy conversion in our cells!
6. Draw a simplified diagram illustrating the steps of the citric acid cycle. Instead
of drawing the molecules in detail, however, draw them as carbon chains,
ignoring any attached atoms. This will give you a better idea of how carbon enters
and leaves the citric acid cycle. This diagram of glycolysis is a useful model to
follow when deciding how to depict the reactions, but of course you will be
showing different reactions occurring in a cycle:
http://adapaproject.org/images/biobook_images/Glycolysis_overview.gif
7: How does fermentation differ from aerobic respiration? What is one advantage
of fermentation? What is one disadvantage of fermentation? Name two different
waste products that can be produced by fermentation.
8: Choose one of the enzymes involved in glycolysis and explain the logic behind
their naming. Here is an example to get you started:
"Phosphofructokinase is a kinase enzyme - one that adds/removes phosphate
groups from a molecule. It adds a phosphate group to fructose-6-phosphate to
turn it into fructose-1,6-bisphosphate. The fructo- in its name refers to its target
being fructose. The phospho- in its name means that the fructose that it targets
already has one phosphate added."
9: a) "Uncoupling proteins" can be embedded in the inner mitochondrial
membrane, allowing protons (H+) to cross the membrane without driving the
ATPase enzyme. What effect would this have on the ability of the mitochondrion
to maintain a proton gradient? What effect would this have on ATP production?
b) Energy cannot be created or destroyed, so any energy harvested via the
electron transport chain must go somewhere. What happens to energy harvested
from glucose when uncoupling proteins are present? How might this be useful to
some organisms?