Download Microbiology- Ch 8- Metabolism

Microbial Metabolism
Ch. 8- pg 216
Metabolism- Greek- to change
Enzymes
What is metabolism?

The sum of chemical
reactions within a
living organism
C6H12O6 + 6O2
6CO2 + 6H2O
+ energy
e-
Why do we need to know about
microbial metabolism?
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Metabolism is the basis of all life, not just
microbes
Metabolism forms the basis of all forms of
microbiology from environmental microbiology
to medical microbiology
If your interest is in human health, knowledge
of metabolism forms the basis of antibiotic
therapy. Some antibiotics interfere with
metabolic reactions
Catabolic and Anabolic reactions
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Catabolism
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degradative; breaks the bonds of larger molecules forming
smaller molecules; releases energy
Generally hydrolytic- absorbs water
exergonic (produce energy)-energy stored in chemical bonds
is released
Anabolism
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biosynthesis; process that forms larger macromolecules from
smaller molecules; requires energy input
Generally dehydration synthesis reactions (release water)
Endergonic (consume energy)
Enzymes-the driving force of
metabolic reactions
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An enzyme is a biological catalyst that speeds
up chemical reactions is the cell
Increase the rate of a chemical reaction 108-1010
times – to the speed of life
Specific for a particular substrate and reaction
The unique three-dimensional shape of an
enzyme allows it to recognize its substrate
How do enzymes work?
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Decrease the activation
energy, the energy
required to initiate a
chemical reaction
Enzymes have an active
site at which only specific
reactants or substrates
are positioned for various
interactions.
Pg 219-text
Enzyme-substrate interaction
Active site
Turnover number
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Enzymes participate in chemical reactions but are not
consumed by them (can function over and over again)
An enzymes speed or turnover number is the
maximum number of substrate molecules an enzyme
molecule can convert to product each second
Enzyme speeds can range over several orders of
magnitude but are characteristic of a particular enzyme
Examples
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DNA polymerase (DNA synthesis)
Catalase (breakdown of H2O2)
15
20,000
Enzyme components
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Simple enzymes- consist entirely of protein
Conjugated enzymes (Holoenzyme )consist of:
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Apoenzyme-the protein component
Cofactor-non protein component
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metallic cofactors – iron, copper, magnesium, calcium
vitamins , organic molecules (coenzyme)
Apoenzyme + cofactor = Holoenzyme
In the absence of the cofactor, the apoenzyme is inactive
Coenzymes
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Can act in catalysis by accepting a
chemical group from one substrate
and transferring it to another
substrate
Some act as electron carriers
Many are derived from vitamins.
Examples:
 vitamin B6-coenzyme in amino
acid metabolism,
 Folic acid-coenzyme in the
synthesis of nucleotides
Important coenzymes in cellular
metabolism

Nicotinamide adenine dinucleotide (NAD+)
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Nicotinamide adenine dinucleotide phosphate
(NADP+)
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NAD+ is involved in catabolic reactions
NADP+ is involved in anabolic reactions
Both NAD+ and NADPH are derivatives of vitamin
B1 (niacin) and they both function as electron
carriers
Other key coenzymes

The flavin coenzymes
Flavin mononucleotide (FMN) and flavin adenine
dinucleotide (FAD)
 Derivatives of vitamin B2 (riboflavin)
 Also act as electron carriers
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Coenzyme A
Derivative of vitamin B5 (pantothenic acid)
 Important roles in fat metabolism and the TCA
(Tricarboxylic Acid) cycle
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Naming enzymes-substrate acted on or type of reaction
Class (-”-ase”)
Type of chemical reaction
Oxidoreductase
Oxidation-reduction (redox) reactions. Loss or gain
of electrons.
Transferase
Transfer of functional groups, such as an amino or
a phosphate group
Hydrolase
Cleaves bonds on molecules with the addition of
water (hydrolysis)
Lyase
Removal or addition of groups of atoms without
hydrolysis
Isomerase
Rearrangement of atoms within a molecule
Ligase
Joining two molecules (using energy from the
breakdown of ATP)
See pg 224- Microbits 8.3- The enzyme Name Game
Oxidation-Reduction Reactions
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Oxidation- loss or removal of electrons
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Reduction- gain of electrons
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Many substances combine with oxygen and transfer elections
to oxygen. Substance becomes oxidized
If another electron receptor is present, oxygen does not need
to be present.
Substance becomes reduced.
Because oxidation and reduction must occur
simultaneously, reactions of called redox reactions.
Comparison of oxidation and
Reduction
Oxidation
 Loss of electrons
 Gain of oxygen
 Loss of hydrogen
 Loss of energry-liberates
energy
 Exothermic, exergonic
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Gives off heat
Reduction
 Gain of electrons
 Loss of oxygen
 Gain of hydrogen
 Gain of energy- energy
stored in reduced
compound
 Endothermic; endergonic
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Requires energy, such as
heat.
Factors affecting enzymatic activity
-rate of chemical reactions
increases with temperature
-most enzymes have a pH
optimum
-elevation above a certain
temperature reduces
enzymatic activity due to
denaturation of the enzyme
-changes in pH can cause
result in alterations in the
3D-structure of the enzyme
leading to denaturation
-high substrate concentration
leads to maximal enzyme
activity, the enzyme is said to
be saturated
-under normal conditions
enzymes are not saturated
Exo and endoenzymes
Exoenzymes
 Active outside
the cell
 Breakdown of
nutrients that are
too large to enter
the cell.
 Some play a role
in disease e.g.,
Streptokinase;
phospholipase C
Endoenzymes
 Most metabolic
enzymes are
endoenzymes
Control of metabolic pathways
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Metabolic pathways are
controlled at the level of
their enzymes
Control of enzymes
Synthesis
 Activity
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Production of enzymes in the cell
Enzymes can be produced at constant
levels in the cell (constitutive enzymes)
OR
Their production can be regulated in
response to substrate( induced enzymes)
or product concentrations (feedback
mechanisms).
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Constitutive enzymes – always present,
always produced in equal amounts or at
equal rates, regardless of amount of
substrate
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enzymes involved in glucose metabolism
Regulated enzymes – not constantly
present; production is turned on (induced) or
turned off (repressed) in response to changes
in concentration of the substrate
Enzyme Inhibitors
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An effective way to control the growth of
bacteria is to control their enzymes
Certain poisons such as cyanide, arsenic and
mercury combine with enzymes and inhibit their
activity
Enzyme inhibitors can be classed as
Competitive inhibitors
 Noncompetitive inhibitors
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Competitive inhibitors
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Fill the active site and compete
with substrate
Similar in shape and chemical
structure to the substrate
Does not undergo any reaction to
form products
May bind reversibly or irreversibly.
e.g., Inhibition of folic acid
synthesis by sulfanilamide
Noncompetitive inhibitors
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Interact with a site other
than the active site
(allosteric or regulatory
site)
Binding of the inhibitor
causes a change in the
shape of the active site,
making it nonfunctional
(allosteric inhibition)
May bind reversibly or
irreversibly
Enzyme Repression
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The end-product of the reaction signals back to
the DNA to turn off expression of the gene
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Prevents the cell from wasting energy
The Cell’s Energy Machine