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TORTORA • FUNKE
• CASE
Microbiology
AN INTRODUCTION
EIGHTH EDITION
B.E Pruitt & Jane J. Stein
Chapter 5
Microbial Metabolism
PowerPoint® Lecture Slide Presentation prepared by Christine L. Case
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Microbial Metabolism
• Metabolism is the sum of the chemical reactions
in an organism.
• Catabolism is the energy-releasing processes,
catabolic, degradative,generally hydrolytic
reaction (use water and break chemical bonds).
• Exergonic – produce more energy than
consume
• Anabolism is the energy-using processes,
anabolic, biosynthetic, building of complex
molecules from simpler ones, involve dehydration
synthesis reactions (reactions that release water)
• Endergonic – consume more energy that
produce.
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Microbial Metabolism
• Catabolism provides the building blocks and energy for
anabolism.
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Figure 5.1
ATP stores energy from catabolic reactions and releases
it later to drive anabolic reactions and perform other
cellular work.
The coupling or energy requiring and energy releasing
reaction is made possible through the molecule
adenosine triphosphate (ATP)
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ATP
• Is made by dehydration synthesis.
• Is broken by hydrolysis to liberate useful energy for the
cell.
When the terminal phosphate group splits from ATP,
adenosine diphosphate is formed and energy is released to
drive anabolic reactions
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• A metabolic pathway is a sequence of enzymatically
catalyzed chemical reactions in a cell.
• Metabolic pathways are determined by enzymes.
• Enzymes are proteins encoded by genes.
• The collision theory states that chemical reactions
can occur when atoms, ions, and molecules collide.
• Reaction rate is the frequency of collisions with
enough energy to bring about a reaction.
• Reaction rate can be increased by enzymes or by
increasing temperature or pressure.
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Catalyst
• Catalyst speeds up a chemical reaction without
being permanently altered themselves
• Enzymes are biological catalyst, specific for a
chemical reaction, acts on a specific substance
called a substrate
• The enzyme orients the substrate into position that
increases the probability of a reaction
• Enzyme substrate complex forms by the
temporary binding of enzyme and substrate enable
the collison to be more effective and lowers the
activation energy of the reaction
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Enzymes
•Apoenzyme: protein portion of an enzyme, can be the
whole enzyme
•Cofactor: Nonprotein component, help catalyze by
forming a bridge between the enzyme and the substrate
•Coenzyme: Organic cofactor, NAD+NADP+FAD
Coenzyme A, may assist the enzymatic reaction by
accepting atoms removed from the substrate or by
donating atoms required by the substrate, electron
carriers
•Holoenzyme: Apoenzyme + cofactor (coenzyme)
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Figure 5.3
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Enzyme Classification
6 classes, named for type of chemical reaction they catalyze
• Oxidoreductase
Oxidation-reduction
reactions
• Transferase
Transfer functional groups
• Hydrolase
Hydrolysis
• Lyase
Removal of atoms without
hydrolysis
• Isomerase
Rearrangement of atoms
• Ligase
Joining of molecules, uses ATP
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Factors Influencing Enzyme Activity
• Enzymes can be denatured by temperature and pH
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Figure 5.6
Factors Influencing Enzyme Activity
• Temperature
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pH
Figure 5.5a
Factors Influencing Enzyme Activity
• Competitive inhibition – inhibitors fill the active site of
an enzyme and compete with the normal substrate for
the active site
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Figure 5.7a, b
Factors Influencing Enzyme Activity
Ex – PABA is an essential nutrient of many bacteria
in the synthesis of folic acid. Sulfanilamide binds to
the enzyme that converts PABA to folic acid,
bacteria cannot grow
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Factors Influencing Enzyme Activity
• Noncompetitive inhibition- inhibitor interacts with
another part of the enzyme
• Allosteric inhibitor –inhibitor binds to a site other
than the substrate binding site and cause the active
site to change shape making it non-functional
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Figure 5.7a, c
Factors Influencing Enzyme Activity
• Feedback
inhibition – a series
of enzymes make an
end product that
inhibits the first
enzyme in the
series, this shuts
down the entire
pathway when
sufficient end
product has been
made
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Figure 5.8
Energy Production
• Nutrient molecules have energy associated with
electrons that form bonds between their atoms
• Reactions in catabolic pathways convert this energy
into bonds of ATP, which serves as a convenient
energy carrier
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Oxidation-Reduction
• Oxidation is the removal of electrons.
• Reduction is the gain of electrons.
• Redox reaction is an oxidation reaction paired with a
reduction reaction.
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Figure 5.9
Oxidation-Reduction
• In biological systems, the electrons are often
associated with hydrogen atoms. Biological oxidations
are often dehydrogenations.
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Figure 5.10
Energy Production
• Cells use redox reactions in catabolism to extract energy
from nutrient molecules
• Cells take nutrients, degrade them from a highly reduced
compound with a lot of hydrogen atoms to a highly
oxidized compound which can serve as an energy
source
• Ex – a cell oxidizes a molecule of glucose C6H12C6 to
CO2 and H2O, the energy in glucose is removed in a
stepwise manner and ultimately trapped by
ATP
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• To produce energy from glucose microbes use two
general processes
• Cellular respiration
• Fermentation
• Both start with glycolysis but follow different
subsequent pathways
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The Generation of ATP
• ATP is generated by the phosphorylation of ADP.
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Carbohydrate Catabolism
• Most organisms oxidize carbohydrates as their primary
source of cellular energy, most common is glucose
• The breakdown of carbohydrates to release energy
• Glycolysis
• Krebs cycle
• Electron transport chain
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Glycolysis
• The oxidation of glucose to pyruvic acid, produces ATP
and NADH.
6-carbon sugar is
split into 2 3carbon sugars, the
sugar is oxidized,
releasing energy
and their atoms
rearrange to form 2
molecules of
pyruvic acid
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1 - 6 carbon sugar
2 - 3 carbon sugars
Preparatory Stage
Preparatory
Stage
Glucose
1
Glucose
6-phosphate
• 2 ATPs are used
2
• Glucose is split to
form 2 Glucose-3phosphate
Fructose
6-phosphate
3
4
Fructose
1,6-diphosphate
5
Dihydroxyacetone
phosphate (DHAP)
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Glyceraldehyde
3-phosphate
(GP)
Figure 5.12.1
Energy-Conserving Stage
• 2 Glucose-3phosphate oxidized
to 2 Pyruvic acid
• 4 ATP produced
6
1,3-diphosphoglyceric acid
7
• 2 NADH produced
• Net 2 ATP
3-phosphoglyceric acid
8
2-phosphoglyceric acid
9
Phosphoenolpyruvic acid
(PEP)
10
Pyruvic acid
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Figure 5.12.2
Pyruvic Acid
• Pyruvic acid can be channeled into the next
step of either fermentation of cellular
respiration
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Alternatives to Glycolysis
• Pentose phosphate pathway:
• Uses pentoses and NADPH
• Operates with glycolysis
• Entner-Doudoroff pathway:
• Produces NADPH and ATP
• Does not involve glycolysis
• Pseudomonas, Rhizobium, Agrobacterium
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Cellular Respiration
• ATP generating process in which molecules are
oxidized and the final electron acceptor is almost
always an inorganic molecule
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Intermediate Step
•Pyruvic acid (from glycolysis) cannot enter the Krebs
cycle directly
•In a preparatory step it most lose one molecule of
CO2 and becomes a two carbon compound
(decarboyxlated)
•The 2c-carbon complex – acetyl group attaches to
coenzyme A through a high energy bond
•Result is acetyl-coenzyme A, 2 acetyl-CoA per
glucose
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Krebs Cycle – TCA cycle – Citric Acid Cycle
• Series of redox
reactions that
transfer potential
energy in the
form of electrons
to electron
carriers, chiefly
NAD
• For every AcetylCoA – 2 ATP, 4
CO2, 6 NADH, 2
FADH
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The Electron Transport Chain
• A series of carrier molecules that are, in turn, oxidized
and reduced as electrons are passed down the chain.
• Series of reductions that indirectly transfer the energy
stored in the coenzymes formed in the Krebs cycle to
ATP
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Respiration
• Aerobic respiration: The final electron acceptor in the
electron transport chain is molecular oxygen (O2).
• In prokaryotes – results in 38 ATP
• In eukaryotes – results in 36 ATP, lose energy shuttling
electrons across mitochondria membrane
• Anaerobic respiration: The final electron acceptor in
the electron transport chain is not O2. Yields less
energy than aerobic respiration because only part of
the Krebs cycles operations under anaerobic
conditions.
• ATP levels vary with the organism and the pathway,
not all carrier in the electron transport chain are
used
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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Pathway
Eukaryote
Prokaryote
Glycolysis
Cytoplasm
Cytoplasm
Intermediate step
Cytoplasm
Cytoplasm
Krebs cycle
Mitochondrial matrix
Cytoplasm
ETC
Mitochondrial inner
membrane
Plasma
membrane
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Fermentation
• Glucose can be converted to another organic product
in fermentation
• Releases energy from oxidation of organic molecules
• Does not require oxygen
• Does not use the Krebs cycle or ETC
• Uses an organic molecule as the final electron
acceptor
• Produces only a small amount of ATP
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Fermentation
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Figure 5.18b
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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Other Energy Sources
• Microbes can oxidize lipids and proteins for energy
• Lipids are broken down by lipases which break fats
down into fatty acids and glycerol components. Each
component is then metabolized separately
• Beneficial for oil spills
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Lipid Catabolism
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Figure 5.20
• Proteins are broken down by proteases and
peptidases which break down proteins to amino
acids and then convert them by
deamination,(removal of the amino group, to enter
the Krebs cycle. The amino group is converted to an
ammonia ion which can be excreted from the cell.
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Protein Catabolism
Protein
Extracellular
proteases
Deamination, decarboxylation,
dehydrogenation
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Amino acids
Organic acid
Krebs cycle
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Biochemical tests
• Used to identify
bacteria.
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Photosynthesis
• Photo: Conversion of light energy into chemical energy
(ATP)
• Synthesis: Fixing carbon into organic molecules
• Photosynthesis – synthesis of complex organic
compounds from single inorganic substances
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Photosynthesis
• Conversion of light energy from the sun into chemical
energy
• Chemical energy is used to convert CO2 from
atmosphere to more reduced carbon compounds,
primarily sugars
• Synthesis of sugar by using carbon atoms from CO2
gas is call carbon fixation
• In photosynthesis electrons are taken from hydrogen
atoms of water, an energy poor molecule, and
incorporated into sugar, an energy rich molecule
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•Species that use light energy are phototrophs.
•Species that obtain energy from chemicals in their
environment are chemotrophs.
•Organisms that need only CO2 as a carbon source are
autotrophs.
•Organisms that require at least one organic nutrient as a
carbon source are heterotrophs.
•These categories of energy source and carbon source
can be combined to group prokaryotes according to
four major modes of nutrition.
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• Photoautotrophs are photosynthetic organisms that
harness light energy to drive the synthesis of organic
compounds from carbon dioxide.
• Chemoautotrophs need only CO2 as a carbon
source, but they obtain energy by oxidizing
inorganic substances, rather than light.
• These substances include hydrogen sulfide (H2S),
ammonia (NH3), and ferrous ions (Fe2+) among others.
• This nutritional mode is unique to prokaryotes.
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•Photoheterotrophs use light to generate ATP but
obtain their carbon in organic form.
•This mode is restricted to prokaryotes.
•Chemoheterotrophs must consume organic
molecules for both energy and carbon.
•This nutritional mode is found widely in prokaryotes,
protists, fungi, animals, and even some parasitic plants.
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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Metabolic Diversity Among Organisms
Nutritional type
Energy
source
Carbon source
Example
Photoautotroph
Light
CO2
Oxygenic:
Cyanobacteria plants.
Anoxygenic: Green,
purple bacteria.
Photoheterotroph
Light
Organic
compounds
Green, purple
nonsulfur bacteria.
Chemoautotroph
Chemical
CO2
Iron-oxidizing
bacteria.
Organic
compounds
Fermentative bacteria.
Animals, protozoa,
fungi, bacteria.
Chemoheterotroph Chemical
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Amphibolic pathways
• Are metabolic pathways that have both catabolic and
anabolic functions.
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Figure 5.32.1
Amphibolic pathways
Most of the ATP made by the cell is used in the
production of new cellular components
Amphibolic pathways bridge the reactions that lead to the
breakdown and synthesis of carbohydrates, lipids,
proteins and nucleus.
These pathways allow for the simultaneous reactions to
occur in which the breakdown products formed in one
reaction are used in another reaction to synthesize a
different compound, or vice versa
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Figure 5.32.2