Biology 123 SI- Dr. Raut’s Class
Session Nine-2/16/2015
1. What are the two different types of enzyme inhibitors? How do they work?
The two different types of enzyme inhibitors are competitive and noncompetitive inhibitors.
Competitive inhibitors compete with the substrate by binding to the active site. Noncompetitive
inhibitors bind to the enzyme at a spot other than the active site, modifying the shape of the active site
and making it impossible for the substrate to bind.
2. Define allosteric regulation.
Allosteric regulation is any case where the proteins function at an active site is affected by the binding of
a regulatory molecule at another site. This can be done either through an activator or an inhibitor. Most
enzymes have two forms, an active form and an inactive form, which the protein tends to oscillate
between the two without regulation. An activator will bind to a regulatory site and will cause the
enzyme to be locked in the active form. An inhibitor will bind to a regulatory site and will cause enzyme
to be locked in the inactive form.
3. What is cooperativity?
Cooperativity is the mechanism in which the binding of one substrate molecule primes the enzyme to
make it easier for additional substrate molecules to bind. Hemaglobbin is an example of this. One
hemaglobbin molecule can hold four O2 molecules. The first O2 molecule binds and locks the enzyme in
a stabilized active form and makes it easier for the other three O2 molecules to bind.
4. What does enzyme regulation have to do with feedback pathways?
Many feedback pathways, particularly negative feedback, will use allosteric binding to affect the
production of a product.
5. List and describe the three types of major catabolic processes.
The three major catabolic processes are fermentation, anaerobic respiration, and aerobic respiration.
Fermentation is the partial breakdown of sugars or other organic fuel without the use of O2 or another
electronegative molecule. In fermentation, an organic molecule typically acts as the final electron
acceptor. Anaerobic respiration harvests chemical energy without oxygen. Anaerobic respiration will use
another electronegative molecule like SO42- or NO3-. Aerobic respiration uses oxygen as the final electron
receptor. Both aerobic and anaerobic respiration are considered cellular respiration.
6. What are oxidation, reduction, an oxidizing agent, and a reducing agent?
Oxidation is the loss of electrons. Reduction is the gain of electrons. An oxidizing agent is the electron
acceptor. A reducing agent is the electron donor. The oxidizing agent is being reduced, and the reducing
agent is being oxidized.
7. What is being oxidized and reduced in the following equation? What is the oxidizing agent, and what
is the reducing agent?
Mg + 2 Cl → Mg2+ + 2 Cl-
Mg is giving electrons to Cl. Therefore, Mg is being oxidized and is the reducing agent. Cl is accepting
electrons from Mg. Therefore, Cl is being reduced and is the oxidizing agent.
8. What is the equation for cellular respiration? What is being oxidized, and what is being reduced?
C6H12O6 + 6 O2 → 6 H2O + 6 CO2
C6H12O6 is being oxidized and is the reducing agent. O2 is being reduced and is the oxidizing agent.
9. Why is cellular respiration a step-wise process instead of occurring all at once?
If the reaction was uncontrolled, then it would be impossible for our cells to capture all of the energy
that is released during the breakdown of organic molecules. By releasing the energy slowly, cell can use
substrate-level phosphorylation and electron acceptors to extract more of the energy, making the
process more efficient.
10. What are the two main oxidizing agents in cellular respiration? What is the oxidized form and
reduced form of these oxidizing agents?
The two main oxidizing agents used in cellular respiration are NAD+ and FADH. These molecules function
in much of the same way. During the reaction, two protons and two electrons, so two H atoms, are
produced. FADH and NAD+ capture one proton and both electrons, which are then carried into the
electron transport chain to produce ATP. The oxidized form of these compounds are NAD+ and FADH.
This is the form they are in before they accept electrons. After they accept electrons, they are turned
into their reduced forms which are NADH and FADH2.
11. True or false: Glycolysis requires oxygen.
False. Glycolysis does not require oxygen, and therefore, by itself glycolysis is considered anaerobic
respiration.
12. Where does glycolysis occur?
While most of cellular respiration occurs in the mitochondria, glycolysis actually occurs in the cytoplasm.
13. What is substrate-level phosphorylation?
Substrate-level phosphorylation is the process by which ATP is directly produced during glycolysis and
the citric acid cycle. During the process, an enzyme take a phosphate group off of a substrate molecule
and move it onto an ADP, creating ATP.
14. What are the four parts of cellular respiration? Which one produces the most ATP?
The four parts of cellular respiration are glycolysis, the oxidation of pyruvate, the citric acid cycle, and
oxidative phosphorylation through the electron transport chain and chemiosmosis. Oxidative
phosphorylation is the addition of an inorganic phosphate onto an ADP and is powered by the redox
reactions of the electron transport chain. Chemiosmosis is the process in which energy is stored through
the use of a hydrogen ion gradient across a membrane, which in the electron transport chain drives ATP
production. Oxidative phosphorylation by far produces the most ATP directly. Glycolysis and the citric
acid cycle will produce a small amount of ATP through substrate-level phosphorylation; however, most
ATP will be produced by using all of those electrons stored in NADH and FADH2.
15. What are the two phases of glycolysis?
The two phases of glycolysis are the energy investment phase and the energy pay off phase. Two ATP
are put in to get the process started (energy investment). Four ATP are produced by substrate-level
phosphorylation (energy pay off). Additionally, 2 NADH are produced and pyruvate is made which will
continue on through the process.
16. Draw out glycolysis. Understand what is happening at each step. You will not have to memorize the
entire process, but you should be able to tell Dr. Raut exactly what is happening at each step if she gives
you the information to do so.
17. In an experiment, changing the pH from 7 to 6 resulted in an increase in product formation. From
this we could conclude that
a. the enzyme became saturated at pH 6.
b. the enzyme’s optimal pH is 6.
c. this enzyme works best at a neutral pH.
d. the temperature must have increased when the pH was changed to 6.
e. the enzyme was in a more active shape at pH 6.
18. Some prokaryotes us anaerobic respiration, a process that
a. does not involve an electron transport chain.
b. produces ATP solely b substrate-level phosphorylation.
c. uses a substance other than oxygen as the final electron acceptor.
d. does not rely on chemiosmosis for the production of ATP.
e. Both a and b are correct.