CHAPTER 5
MICROBIAL METABOLISM
I.
Catabolic and Anabolic Reactions
A.
Metabolism - The sum of all chemical reactions within a living cell
either releasing or requiring energy. (Overhead) Fig 5.1
1.
2.
II.
Enzymes
A.
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Catabolism - Breaking down complex organic compounds into
simpler ones.
a)
Usually release energy
b)
Released energy is transferred to and trapped in ATP. Some is
given off as heat.
c)
Released energy is used to drive anabolic reactions
Anabolism- The building of complex organic molecules from simpler
ones.
a)
For example: Formation of proteins from amino acids, nucleic
acids from nucleotides, polysaccharides from simple sugars.
These materials are used for cell growth.
b)
Reactions usually require energy from ATP.
Overhead Fig 5.4
Descriptions
1.
Proteins produced by living cells that that use them to catalyze
chemical reactions.
2.
Names usually end in -ase
3.
When enzyme and substrate combine, substrate is transformed and
enzyme is recovered. Fig 5.4
4.
Operate at optimum temperature and pH fig 5.5a,b,c fig 5.6
5.
Reaction is often controlled by feedback inhibition - End product
inhibits an enzyme’s activity somewhere in the pathway. Fig 5.8
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III.
Energy Production
A.
B.
Oxidation-Reduction with transfer of energy
1.
Oxidation is removing electrons; Reduction is gaining. Fig 5.9
2.
Each time a substance is oxidized another is reduced.
3.
Most biological oxidation is by loss of hydrogen atoms (H+ and e-), so
is called dehydrogenation reaction. Fig 5.10 Example: NAD+ is the
oxidized form; NADH is the reduced form (overhead). NADH used to
capture and transfer energy.
4.
Energy is released during a cell’s oxidation of glucose as hydrogens
are removed.
Generation of Adenosine Triphosphate (ATP) for Energy Storage
(see chapter fig 2.18)
1.
IV.
ADP traps energy released by certain metabolic reactions (especially
catabolism of glucose) to form ATP. Stored as ATP until needed.
Biochemical Pathways of Energy Production
A.
Description: Series of enzymatically catalyzed reactions called
biochemical pathways store energy in and release energy from
organic molecules. Ex.: Fig 5.12 Appendix C fig C.2
B.
Carbohydrate Metabolism
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1.
Most of a cell’s energy is produced from the oxidation of
carbohydrate - Most commonly glucose
2.
Two major types of glucose catabolism are:
Fig 5.11
a)
Respiration, in which glucose is completely broken down to CO2
and H20 creating much ATP. The final electron acceptor in this
oxidation is usually 02, but may be other inorganic ions. This
happens in the mitochondria of eukaryotes.
b)
Fermentation in which it is partially broken down producing
small amounts of ATP and using no 02 .
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3.
A common pathway to both respiration and fermentation is glycolysis
(there are alternate pathways). Glucose (6 carbons) is oxidized (using
no 02 ) to 2 pyruvic acids (3 carbons) with production of some ATP
and energy containing NADH. Fig 5.11, fig 5.12
4.
Respiration using 02 is called aerobic respiration. Fig 5.11
Once glycolysis is completed and pyruvic acid is made two other
metabolic pathways are used sequentially: the Krebs cycle and, the
electron transport chain (ETC)
5.
6.
a)
Krebs cycle is the oxidation of a derivative of pyruvate (acetyl
CoA) to CO2 with production of some ATP, and energy
containing NADH and FADH2. 2 ATP are produced. fig 5.13,
Appendix C5.
b)
Electron transport chain where NADH and FADH2 are oxidized
and give up their electrons to a series of carrier molecules in a
membrane. As the electrons come off the last carrier they
combine with O2 and H+ to form H2O water. Fig 5.14 Energy is
released in a stepwise manner to produce a considerable amount
of ATP (34 from 1 glucose). Notice that the ATP is produced as
H+ moves thru a special protein channel in the membrane. Fig
5.15, fig 5.16.
c)
Summary of respiration. Fig 5.17. Table 5.3. Large amounts of
ATP made, O2 used as final electron acceptor, CO2 and H2O are
wastes products.
Respiration without 02 is called anaerobic respiration.
a)
anaerobic - inorganic molecule other than O2 . Table 5.5 p 135.
b)
Example: Some bacteria such as Pseudomonas and Bacillus can
use nitrate ion (NO3-) as final electron acceptor. Since not all
the carriers in the ETC participate in anaerobic respiration, the
amount of ATP produced is never as much as aerobic respiration
but still much better than fermentation.
Fermentation – the pyruvate made during glycolysis is converted to
an organic product. Fig 5.18
a)
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Releases energy from sugars or other organic molecules by
oxidation. Only 2 ATP produced per glucose molecule. Does not
use the Krebs cycle or the ETC.
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7.
C.
b)
O2 is not required in fermentation
c)
Final electron acceptor is an organic molecule
d)
Examples :Two end products can be alcohol or lactic acid. Fig
5.19, Table 5.4 p135.
Biochemical Tests a)
Bacteria and yeasts can be identified by detecting the action of
their enzymes on substrates.
b)
Fermentation tests are used to determine whether an organism
can ferment a carbohydrate to produce acid and gas.
Photosynthesis
1.
6 CO2 + 12 H2O + light energy
2.
Converts light energy from the sun into chemical energy. Fig 5.24
a)
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C6H12O6 + 6O2 + 6H2O
Light dependent- Photophosphorylation
(1)
Cyclic- Electrons return to chlorophyll
(2)
Non-cyclic- Electron are incorporated into NADPH and
products are ATP & O2
(3)
Cyanobacteria and algae
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3.
D.
V.
Other Catabolic Reactions
1.
Lipid - Lipases hydrolyze lipids into glycerol and fatty acids. Glycerol
and the fatty acids are then broken down in the Krebs cycle.
2.
Protein – Proteins are broken down by proteases and peptidases to
amino acids that are converted to various substances that enter the
Krebs cycle.
a)
Amino acid is deaminated where an NH2 is removed so it can
enter the Krebs cycle.
b)
Also maybe decarboxylated where COOH is removed.
Biochemical Pathways of Energy Use (Anabolism)
A.
VI.
Dark reaction- Electrons from light dependent + energy from ATP
reduce CO2 to sugar.
Biosynthesis = production of new cellular components from simple
molecules. Examples:
1.
Polysaccharides - Glycogen and basic material for peptidoglycan. Fig
5.28.
2.
Lipids -Made from glycerol (produced during glycolysis) and fatty
acids (produced from acetyl CoA during preparatory step for the
Krebs cycle). Fig 5.29.
3.
Purines and pyrimidines are part of the nucleotide subunits needed to
make DNA and RNA. Amino acids made from intermediates of
glycolysis and the Krebs cycle participate in the synthesis of purines
and pyrimidines. Fig 5.31
Metabolic Diversity Among Organisms
A.
Nutritional Classification by energy and carbon source - Figure 5.27
1.
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Energy
a)
Phototrophs - Use light as their primary energy source
b)
Chemotrophs - Depend upon oxidation-reduction reactions of
inorganic or organic compounds for energy.
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2.
3.
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Carbon Source
a)
Autotrophs - Use carbon dioxide
b)
Heterotrophs - Require an organic carbon source
Combination
a)
Photoautotrophs
b)
Photohererotrophs
c)
Chemoautotrophs
d)
Chemoheterotrophs - Most medically important organisms are in
this group.
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