Download Microbial Metabolism

Microbial Metabolism
Metabolism refers to all chemical reactions that occur
Chapter 5:
within a living a living organism.
These chemical reactions are generally of two types:
Microbial Metabolism
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Catabolic:: Degradative reactions that release energy by
Catabolic
breaking down large, complex molecules into smaller ones.
Often involve hydrolysis
hydrolysis,, breaking bonds with water.
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Anabolic:: Biosynthetic reactions that build large
Anabolic
complex molecules from simpler ones.
Require energy and often involve dehydration synthesis.
synthesis.
Coupling of Anabolic and Catabolic Reactions
Catabolic reactions provide the energy needed to
drive anabolic reactions.
u ATP stores energy from catabolic reactions and
releases it to drive anabolic reactions.
u Catabolic reactions are often coupled to ATP
synthesis::
synthesis
ADP + Pi + Energy --------------------->
> ATP
u Anabolic reactions are often coupled to ATP
hydrolysis:
ATP --------------------->
> ADP + Pi + Energy
u Efficiency: Only part of the energy released in
catabolism is available for work, the rest is lost
as heat. Energy transformations are inefficient.
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Enzymes
Enzymes (Continued)
Protein molecules that catalyze chemical
reactions.
u Enzymes are highly specific and usually catalyze
only one or a few closely related reactions.
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Sucrase
Sucrose + H2O ----------->
----------->
(substrate)
Glucose + Fructose
(products)
Enzymes are extremely efficient.
efficient. Speed up
reaction up to 10 billion times more than without
enzyme.
u Turnover number:
number: Number of substrate
molecules an enzyme molecule converts to
product each second. Ranges from 1 to 500,000.
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Anabolic and Catabolic Reactions are
Linked by ATP in Living Organisms
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The rate of a chemical reaction depends on
temperature, pressure, substrate
concentration, pH, and several other factors in
the cell.
Energy of activation:
activation : The amount of energy
required to trigger a chemical reaction.
u Enzymes speed up chemical reactions by
decreasing their energy of activation without
increasing the temperature or pressure inside
the cell.
Example: Bring reactants together, create
stress on a bond, etc.
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Enzymes Lower the Energy of
Activation of a Chemical Reaction
Naming Enzymes
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Enzyme names typically end in - ase
ase..
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There are six classes of enzymes
1. Oxidoreductases
Oxidoreductases:: Catalyze oxidationoxidation-reduction
reactions. Include dehydrogenases and oxidases
oxidases..
2. Transferases
Transferases:: Transfer functional groups (amino,
phosphate, etc).
3. Hydrolases
Hydrolases:: Hydrolysis, break bonds by adding
water.
4. Lyases
Lyases:: Remove groups of atoms without hydrolysis.
5. Isomerases : Rearrange atoms within a molecule.
6. Ligases
Ligases:: Join two molecules, usually with energy
provided by ATP hydrolysis.
Enzyme Components
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Some enzymes consist of protein only.
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Others have a protein portion (apoenzyme
(apoenzyme)) and a
nonprotein component (cofactor
(cofactor).
).
Components of a Holoenzyme
Holoenzyme = Apoenzyme + Cofactor
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Enzyme cofactors may be a metal ion (Mg 2+ ,
Ca2+, etc.) or an organic molecule (coenzyme
( coenzyme).
).
Many coenzymes are derived from vitamins.
Examples:
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NAD+: Nicotinamide adenine dinucleotide
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NADP+: Nicotinamide adenine dinucleotide phosphate
are both cofactors derived from niacin (B vitamin).
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Coenzyme A is derived from panthotenic acid.
Mechanism of Enzymatic Action
Surface of enzyme contains an active site that
binds specifically to the substrate.
Mechanism of Enzymatic Action
1. An enzyme
enzyme--substrate complexforms.
complex forms.
2. Substrate molecule is transformed by:
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Rearrangement of existing atoms
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Breakdown of substrate molecule
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Combination with another substrate molecule
3. Products of reaction no longer fit the active
site and are released
released..
4. Unchanged enzyme is free to bind to more
substrate molecules.
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Factors Affecting Enzymatic Action
Enzymes are protein molecules and their threethreedimensional shape is essential for their function.
The shape of the active site must not be altered so
that it can bind specifically to the substrate.
Several factors can affects enzyme activity:
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Denaturation of a Protein Abolishes its
Activity
Temperature: Most enzymes have an optimal
temperature. At low temperatures most reactions
temperature.
proceed slowly due to slow particle movement. At
very high temperatures reactions slow down because
the enzyme is denatured
denatured..
Denaturation: Loss of threeDenaturation:
three-dimensional protein
structure. Involves breakage of H and noncovalent
bonds.
Factors that Affect Enzyme Activity: pH,
Temperature, and Substrate Concentration
Factors Affecting Enzymatic Action
pH: Most enzymes have an optimum pH. Above
or below this value activity slows down. Extreme
changes in pH cause denaturation
denaturation..
u Substrate concentration: Enzyme acts at
maximum rate at high substrate concentration.
Saturation point:
point: Substrate concentration at
which enzyme is acting at maximum rate possible.
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Inhibitors:: Inhibit enzyme activity. Two types:
Inhibitors
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Competitive inhibitors:
inhibitors: Bind to enzyme active site
site..
Example: Sulfa drugs, AZT.
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Noncompetitive inhibitors:
inhibitors: Bind to an allosteric site
site..
Example: Cyanide, fluoride.
Factors Affecting Enzymatic Action
Competitive versus Noncompetitive
Enzyme Inhibitors
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Feedback Inhibition: Also known as end
end-- product
inhibition.
Some allosteric inhibitors stop cell from making
more of a product than it needs.
The end product of a series of reactions, inhibits
the activity of an earlier enzyme.
Enzyme 1
Enzyme 2
Enzyme 3
A --------------->
> B ------------->
> C --------------->
>D
Enzyme 1 is inhibited by product D.
Feedback inhibition is used to regulate ATP, amino
acid, nucleotide, and vitamin synthesis by the cell.
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Feedback Inhibition of an Enzymatic
Pathway
Ribozymes
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Catalytic RNA molecules
Have active sites that bind to substrates
Discovered in 1982
Act on RNA substrates by cutting and splicing
them.
Energy Production
Oxidation-Reduction or Redox Reactions:
OxidationReactions in which both oxidation and
reduction occur.
Oxidation:: Removal of electrons or H atoms
Oxidation
Addition of oxygen
Associated with loss of energy
Reduction:: Gain of electrons or H atoms
Reduction
Loss of oxygen
Associated with gain of energy
Oxidation-Reduction Reactions
Examples : Aerobic respiration & photosynthesis
Examples:
are redox
redoxprocesses.
processes.
ATP Production
Aerobic Respiration is a Redox Reaction
Some of the energy released in oxidationoxidation reduction processes is trapped as ATP; the rest is
lost as heat.
Phosphorylation reaction:
ADP + Energy + P ----------------->
> ATP
There are three different mechanisms of ATP
phosphorylation in living organisms:
1. SubstrateSubstrate - Level Phosphorylation
Phosphorylation::
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C6H12O6 + 6 O2 -----> 6 CO2 + 6 H2O + ATP
Glucose oxygen oxidized reduced
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Direct transfer of phosphate from phosphorylated
compound to ADP.
Simple process that does not require intact membranes.
Generates a small amount of energy during aerobic
respiration.
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Two Mechanisms of ATP Synthesis:
Oxidative and Substrate Level Phosphorylation
2. Oxidative Phosphorylation
Phosphorylation::
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Involves electron transport chain,
chain, in which electrons
are transferred from organic compounds to electron
carriers (NAD+ or FAD)
FAD) to a final electron acceptor
(O2 or other inorganic compounds).
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Occurs on membranes (plasma membrane of
procaryotes or inner mitochondrial membrane of
eucaryotes).
eucaryotes
).
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ATP is generated through chemiosmosis .
Generates most of the ATP in aerobic respiration.
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3. Photophosphorylation
Photophosphorylation::
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Carbohydrate Catabolism
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Most microorganisms use glucose or other
carbohydrates as their primary source of energy.
Lipids and proteins are also used as energy
sources.
Two general processes are used to obtain energy
from glucose: cellular respiration and
fermentation..
fermentation
II. Fermentation:
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Occurs in photosynthetic cells only.
Convert solar energy into chemical energy (ATP and
NADPH).
Also involves an electron transport chain.
Carbohydrate Catabolism
I. Cellular respiration:
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ATP generating process in which food molecules
are oxidized.
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Requires an electron transport chain.
chain .
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Final electron acceptor is an inorganic molecule:
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Aerobic respiration final electron acceptor is oxygen .
Much more efficient process.
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Anaerobic respiration final electron acceptor is
another inorganic molecule
molecule.. Energetically inefficient
process.
Aerobic Respiration versus Fermentation
Releases energy from sugars or other organic
molecules.
Does not require oxygen
oxygen,, but may occur in its
presence.
Does not require an electron transport chain.
Final electron acceptor is organic molecule.
Inefficient:: Produces a small amount of ATP for each
Inefficient
molecule of food.
End--products are energy rich organic compounds:
End
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Lactic acid
Alcohol
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Cellular Respiration
Three Stages of Aerobic Respiration
I. Aerobic Respiration
C6H12O6 + 6 O2 --------->
> 6 CO2 + 6 H2O + ATP
Glucose oxygen oxidized reduced
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Most energy efficient catabolic process.
Oxygen is final electron acceptor.
Aerobic Respiration occurs in three stages:
stages :
1. Glycolysis
2. Kreb’s Cycle
3. Electron Transport & Chemiosmosis
Cellular Respiration
I. Stages of Aerobic Respiration
In Glycolysis Glucose is Split into Two
Molecules of Pyruvic Acid
1. Glycolysis
Glycolysis:: “Splitting of sugar”.
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Glucose (6 C) is split and oxidized to two molecules of
pyruvic acid (3C).
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Most organisms can carry out this process.
Does not require oxygen.
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Net yield per glucose molecule:
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2 ATP (substrate level phosphorylation
phosphorylation))
2 NADH
Cellular Respiration
I. Stages of Aerobic Respiration
2. Krebs Cycle (Citric Acid Cycle):
Cycle):
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Before cycle can start, pyruvic acid (3C) loses one carbon
(as CO2) to become acetyl CoA (2C).
Acetyl CoA (2C) joins oxaloacetic acid (4C) to form citric
acid (6C).
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Cycle of 8 oxidationoxidation-reduction reactions that transfer
energy to electron carrier molecules (coenzymes NAD+
and FAD).
2 molecules of carbon dioxide are lost during each cycle.
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Oxaloacetic acid is regenerated in final step.
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Pyruvic Acid is Converted to Acetyl
CoA Before the Kreb’s Cycle Starts
Net yield per glucose molecule:
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2 ATP (substrate level phosphorylation
phosphorylation))
8 NADH
2 FADH2
Notice that carbon dioxide is lost.
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Kreb’s Cycle: Two Carbons In & Two Out
Cellular Respiration
I. Stages of Aerobic Respiration
3. Electron Transport Chain and Chemiosmosis
Chemiosmosis::
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Electrons from NADH and FADH2 are released to
chain of electron carriers.
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Electron carriers are on cell membrane (plasma
membrane of bacteria or inner mitochondrial
membrane in eucaryotes
eucaryotes).
).
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Final electron acceptor is oxygen
oxygen..
A proton gradient is generated across membrane as
electrons flow down chain.
ATP is made by ATP synthase (chemiosmosis
chemiosmosis)) as
protons flow down concentration gradient.
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Net ATP yield:
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Electron Transport Chain in Aerobic Respiration:
Oxygen is Final Electron Acceptor
Summary of Aerobic Respiration in Procaryotes
2 FADH2 generate 2 ATPs each:
4 ATP
10 NADH generate 3 ATPs each: 30 ATP
Chemiosmosis in Aerobic Respiration:
ATP Synthesis Requires Intact Membranes
Total Yield from Aerobic Respiration of 1
Glucose molecule: 3636 -38 molecules of ATP
In procaryotes
procaryotes::
C6H12O6 + 6 O2--------->
> 6 CO2 + 6 H2O + 38 ATP
In eucaryotes
eucaryotes::
C6H12O6 + 6 O2 --------->
> 6 CO2 + 6 H2O + 36 ATP
Yield is lower in eucaryotes because transport of
pyruvic acid into mitochondria requires energy.
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Fermentation
Cellular Respiration
II. Anaerobic Respiration
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Final electron acceptor is not oxygen.
Instead it is an inorganic molecule:
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Nitrate (NO3-): Pseudomonas and Bacillus . Reduced
to nitrite (NO2-):, nitrous oxide, or nitrogen gas.
Sulfate (SO42-): Desulfovibrio . Reduced to hydrogen
sulfide (H2S).
Carbonate (CO32-): Reduced to methane.
Inefficient (2 ATPs per glucose molecule).
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Only part of the Krebs cycle operates without oxygen.
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Not all carriers in electron transport chain participate.
Anaerobes tend to grow more slowly than aerobes.
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Releases energy from sugars or other organic molecules.
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Does not require oxygen, but may occur in its presence.
Does not require Krebs cycle or an electron transport
chain.
Final electron acceptor is organic molecule.
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Inefficient. Produces a small amount of ATP for each
Inefficient.
molecule of food. (1 or 2 ATPs
ATPs))
End--products may be lactic acid, alcohol, or other energy
End
rich organic compounds.
u Lactic Acid Fermentation:
Fermentation: Carried out by
Lactobacillus and Streptococcus. Can result in food
spoilage. Used to make yogurt, sauerkraut, and pickles.
u Alcohol Fermentation:
Fermentation: Carried out by yeasts and
bacteria.
Fermentation is Less Efficient Than Aerobic Respiration
Alcohol and Lactic Acid Fermentation
Fermentation: Generates Various Energy Rich,
Organic End-Products
Catabolism of Various Organic Food Molecules
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Photosynthesis
6 CO2 + 6 H2O + Light --------->
> C6H12O6 + 6 O2
Light Dependent Reactions
Light energy is trapped by chlorophyll
chlorophyll..
u Water is split into oxygen and hydrogen.
u NADP+ is reduced to NADPH.
u ATP is made.
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u Light Independent Reactions
u Do not require light.
u CO 2 from air is fixed and used to make sugar.
u Sugar is synthesized, using ATP and NADPH.
Four Groups Based on Metabolic Diversity
1. Chemoheterotrophs
Chemoheterotrophs::
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Energy source:
source: Organic compounds.
Carbon source:
source: Organic compounds.
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Metabolic Diversity
Living organisms can be classified based on
where they obtain their energy and carbon.
Energy Source
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Phototrophs: Light is primary energy source.
Phototrophs:
Chemotrophs:: Oxidation of chemical compounds.
Chemotrophs
Carbon Source
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Autotrophs : Carbon dioxide.
Autotrophs:
Heterotrophs:: Organic carbon source.
Heterotrophs
Organisms Are Classified Based on Their
Metabolic Requirements
Examples: Most bacteria, all protozoans
protozoans,, all fungi, and all animals.
2. Chemoautotrophs
Chemoautotrophs::
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Energy source:
source: Inorganic compounds (H2 S, NH3, S, H2 , Fe 2+ , etc.)
Carbon source:
source: Carbon dioxide.
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Examples: Iron, sulfur, hydrogen, and nitrifying bacteria.
3. Photoheterotrophs
Photoheterotrophs::
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Energy source:
source: Light.
Carbon source:
source: Organic compounds.
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Examples: Purple and green nonsulfur bacteria.
4. Photoautotrophs
Photoautotrophs::
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Energy source:
source: Light.
Carbon source:
source: Carbon dioxide.
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Examples: Plants, algae, photosynthetic bacteria
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