MCB 229 Spring 2000 Study Guide 7 Prof.
Terry
Covers Lecture for Feb. 22
This study guide is intended for you to use while you are
doing the assigned text reading. Quiz questions will be made with reference to
topics in this study guide. Quiz #7, based on questions from this study guide,
must be completed by midnight before the class on Tuesday, Feb. 22. You will
need to create your "myWebCT" account and visit the MCB 229 WebCT page in order
to access this quiz.
Chapter 9 (p. 169-174; 176-179); also see Appendix Fig.
AII.4 (p. A16)
- Pyruvate is the end product of glycolysis (or Entner-Doudoroff) pathways.
If an external electron acceptor is available (respiration), then pyruvate can
be further oxidized by the TCA cycle. But pyruvate must first be decarboxylated
(CO2 removed) and oxidized. What is the name of the multienzyme
system that carries out this reaction? What product is produced? What redox
carrier is involved?
- The TCA cycle (a.k.a. Krebs cycle, citric acid cycle)
can works as an "oxidation superburner". It allows electrons to be removed at
several points. Using Fig. 9.7 and/or Fig. AII.4, identify the oxidation
reactions in the TCA pathway (hint: there are 4 of them). What redox carriers
are involved? For one complete cycle, which reduced redox carriers are produced
and in what amounts?
- Do decarboxylation reactions also occur in the TCA
cycle? If so, where?
- I don't require you to memorize the compounds or the
enzymes involved in the TCA cycle, but I do suggest that you spend a couple of
minutes comparing the diagram in Fig. AII.4 with the text on p. 169 (upper right
column).
- Do strictly fermentative organisms use the TCA cycle? Logically
no, since they need to use their pyruvate as an electron acceptor. But most of
the enzymes of the TCA cycle are found in many non-respiring microbes, because
this cycle also serves anabolic needs.
- The electron transport system (ETS)
makes possible respiration, an alternative way to get rid of electrons
produced in oxidation reactions. In fermentation, _________ served as the
acceptor for electrons. In respiration, what serves as the electron acceptor?
___________.
- Where is the electron transport chain located in eucaryotic
cells? ___________ In bacterial cells? ______________ .
- The components of
the ETS include several protein complexes and a couple of electron carriers that
move between the complexes. The identity of these carriers differs between
different organisms. What are the names of principal ETS electron carriers used
in mitochondria (see Fig. 9.8)? (hint: there are 7 of them).
- What does the
chemiosmotic hypothesis predict?
- What is protonmotive force (PMF)? In
bacteria, which side of the membrane has more protons? How do bacteria use the
energy of PMF?
- Compare the structure of ATP synthase with other enzymes;
what is unusual about it? (see Fig. 9.12) Where is this enzyme located? Which
way does the head face in bacterial cells? What does this enzyme do? How does it
get its energy?
- How do chemicals such as cyanide or azide affect
respiration? How do uncouplers such as dinitrophenol or valinomycin affect
respiration?
- What is the maximum theoretical ATP yield from the aerobic
respiration of glucose in mitochondria? Do bacteria obtain the same yields? How
does this compare to the ATP yield from glycolysis?
- Although we usually
equate "respiration" with the consumption of oxygen, some bacteria use other
electron acceptors with a modified ETS; this is called anaerobic respiration.
What electron acceptors are used in anaerobic respiration? What are the reduced
products formed in each case?
- So far, we have looked only at glucose
as an energy source. Microbes can degrade other materials, including a
variety of carbohydrates, lipids, and proteins. In each case, cells need
specific enzymes to activate appropriate catabolic pathways. The remaining few
questions direct your attention to a few of these catabolic reactions, as
described and diagrammed on pp. 178-179. Fear not, the end is near!
- Suppose
the substrate growth is not glucose but some other monosaccharide such as
galactose or fructose. What modifications must the cell make in its catabolic
machinery?
- Suppose the substrate for growth is a disaccharide such as
lactose or sucrose. What modifications must the cell make in its catabolic
machinery?
- Suppose the substrate for growth is a polysaccharide such as
starch. What modifications must the cell make in its catabolic machinery? Are
most bacteria equally able to make adaptations for growth on cellulose? Agar?
- When cells attempt to use lipids as their growth substrate, they must shift
gears dramatically. Fatty acids are often the most abundant energy source in
lipids. What pathway handles fatty acid oxidation? (hint: see Fig. 9.17) What is
the product that enters into central metabolism via the TCA cycle? (hint: it has
2 C-atoms).
- If proteins are used as growth substrates, how are they broken
down? What is the first step in catabolism of amino acids? What major catabolic
pathways subsequently oxidizes these products?
- Whew!!! You're done! I'll try
to be especially kind in writing the quiz questions on this stuff – I know
there's a lot of material here.