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METABOLISM
BACTERIAL METABOLISM
CHAPTER 5
• Metabolism is the sum of the chemical
reactions in an organism.
• Catabolism is the energy-releasing
processes.
• Anabolism is the energy-using processes.
• Catabolism provides the building blocks
and energy for anabolism.
What promotes chemical
reactions?
• The collision theory states that chemical
reactions can occur when atoms, ions, and
molecules collide.
• Activation energy is needed to disrupt electronic
configurations.
• Reaction rate is the frequency of collisions with
enough energy to bring about a reaction.
• Reaction rate can be increased by increasing
temperature, pressure, and reactant
concentration.
What promotes chemical
reactions in biological systems?
Holoenzyme: Apoenzyme +
cofactor
• Enzymes are biological catalysts that can
accelerate reactions without increasing
temperature. (Importance?)
– Specific for a chemical reaction; not used up
in that reaction
• Apoenzyme: protein
• Cofactor: Nonprotein component
– Coenzyme: Organic cofactor
• NAD+, NADP+, FAD, Coenzyme A
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Enzymes change substrate to products
The turnover number is generally
1-10,000 molecules per second.
Enzymes can be denatured by
temperature and pH
Factors that influence an enzyme
Competitive Inhibition of enzyme
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Non-competitive inhibition of
enzyme
Feed-back inhibition of enzyme
• Build-up of end
product inhibits action
of enzyme in previous
reaction (usually first
reaction of pathway)
Classification of enzymes
•
•
•
•
Oxidoreductase
Transferase
Hydrolase
Lyase
• Isomerase
• Ligase
Oxidation-reduction rxns
Transfer functional groups
Hydrolysis
Removal of atoms without
hydrolysis
Rearrangement of atoms
Joining of molecules, uses
ATP
• A metabolic pathway is a sequence of
enzymatically catalyzed chemical
reactions in a cell.
• Metabolic pathways are determined by
enzymes.
• Enzymes are encoded by genes.
Oxidation-reduction reactions
• 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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In biological systems, the electrons are often
associated with hydrogen atoms. Biological
oxidations are often dehydrogenations.
Energy from catabolic reactions is stored in high
energy, unstable bonds of ATP (adenosine
triphosphate) to be used in anabolic reactions.
NADH has more energy than NAD: H+ produced = proton motive force
Types of phosphorylation to
generate ATP
• Substrate-level phosphorylation is the transfer of
a high-energy PO4- to ADP.
Types of phosphorylation to
generate ATP
• Oxidative:
– Energy released from the transfer of electrons
(oxidation) of one compound to another (reduction) is
used to generate ATP by chemiosmosis (electron
transport chain)
• Photophosphorylation:
– Light causes chlorophyll to give up electrons. Energy
released from the transfer of electrons (oxidation) of
chlorophyll through a system of carrier molecules is
used to generate ATP.
Types of Bacterial Metabolism
• Fermentation
• Respiration
– Aerobic Respiration
– Anaerobic Respiration
• Photosynthesis
CARBOHYDRATES
• The breakdown of carbohydrates to
release energy
– Glycolysis
– Krebs cycle
– Electron transport chain
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GLYCOLYSIS (EMBDENMEYERHOFF PATHWAY)
The oxidation of glucose to pyruvic
acid, produces ATP and NADH.
• Respiration and Fermentation have the
same first step: Glycolysis
• Glucose + 2 ATP + 2 ADP + 2 PO4– + 2 NAD+ →
2 pyruvic acid + 4 ATP + 2 NADH + 2H+
• Net gain of 2 ATP; 2 NADH; and 6
precursor metabolites
• Does not require O2
Glycolysis
ALTERNATIVES TO GLYCOLYSIS
• Pentose phosphate pathway (hexose
monophosphate shunt:
– Operates with glycolysis to breakdown 5-C
sugars
– Gain of 1 ATP
Aerobic Respiration
• The COMPLETE breakdown of glucose to
CO2 and H2O with O2 serving as the final
electron acceptor (TEA=terminal electron
acceptor)
• Entner-Doudoroff pathway:
– Produces NADPH and 1 ATP
– Does not involve glycolysis
– Pseudomonas, Rhizobium, Agrobacterium
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Intermediate Step
KREBS CYCLE
• Oxidation of acetyl CoA produces NADH
and FADH2
• AKA Tricarboxylic Acid Cycle (TCA) or
Citric Acid Cycle
• Potential energy stored in acetyl CoA
released in steps to carrier coenzymes
primarily NAD+ to NADH
• Pyruvic acid
(from glycolysis)
is oxidized and
decarboyxlated
Figure 5.13.1
The Electron Transport Chain
• A series of carrier molecules that are, in
turn, oxidized and reduced as electrons
are passed down the chain.
• Energy released can be used to produce
ATP by chemiosmosis.
– Proton motive force: source of energy for
• Synthesis of ATP
• Active Transport of substances across membrane
• Flagella movement
A model for the ETC
Electron Transport Chain
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Respiration
• Aerobic respiration: The final electron
acceptor in the electron transport chain is
molecular oxygen (O2):
– C6H12O6 + 6 O2 + 38ADP +38 P=6 CO2 + 6
H2O + 38ATP
– 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.
Anaerobic respiration
Electron acceptor
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
Products
NO3–
NO2–, N2 + H2O
SO4–
H2S + H2O
CO32 –
CH4 + H2O
Fermentation
Figure 5.14
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Fermentation products can
vary
Fermentation
• Alcohol fermentation. Produces ethyl
alcohol + CO2
• Lactic acid fermentation. Produces lactic
acid.
– Homolactic fermentation. Produces lactic acid
only.
– Heterolactic fermentation. Produces lactic
acid and other compounds.
Fermentation end products
Types of
fermentation
Fermentation
ATP Yield
Figure 5.23
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Comparison of three types of
metabolism
COMPARISON OF METABOLISM
• Aerobic respiration: Total ATP
Prokaryotes=38
Eukaryotes=34
– Final electron receptor is O2
• Anaerobic respiration: ATP >2<38
– Absence of oxygen
– Final electron receptor is inorganic molecule
• Fermentation: Yield = 2 ATP
– Final electron receptor is organic molecule
– Endproducts: Lactic acid/Alcohol
Photosynthesis
Pathway
Eukaryote
Prokaryote
Glycolysis
Cytoplasm
Cytoplasm
Intermediate step
Cytoplasm
Cytoplasm
Krebs cycle
Mitochondrial
matrix
Mitochondrial
inner membrane
Cytoplasm
ETC
• Conversion of light energy to chemical
energy
• C fixation = conversion of CO2 to sugars
• Light dependent stage
• Calvin-Benson cycle
Plasma
membrane
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Nutritional Pattern Classification
Chemotrophs
• Use energy from chemicals.
• Energy:
– Chemoheterotroph
– Phototrophs
– Chemotrophs
Glucose
NAD+
• Carbon source:
ETC
– Autotrophs
– Heterotrophs
Pyruvic acid
• Almost all medically important
microorganisms are chemoheterotrophs.
NADH
ADP + P
ATP
• Energy is used in anabolism.
Phototrophs
Chemotrophs
• Use energy from chemicals.
• Use light energy.
– Chemoautotroph, Thiobacillus ferroxidans
Chlorophyll
2Fe2+
ETC
NAD+
ETC
2Fe3+
NADH
Chlorophyll
oxidized
ADP + P
ADP + P
ATP
ATP
2 H+
– Energy used in Calvin-Benson cycle to fix CO2
• Photoautotrophs use energy in the CalvinBenson cycle to fix CO2.
• Photoheterotrophs use energy.
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