Download Foundations in Microbiology

An Introduction to Microbial
Metabolism
Chapter 8
energy
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The capacity to do work or cause change
Kinetic energy is actively performing work,
Potential energy is stored (ability to perform
work based on location/arrangement)
1st law of thermodynamics – energy
conservation
Endergonic reactions – consume energy
Exergonic reactions – release energy
Endergonic:
X + Y + energy  Z
Exergonic:
X + Y  Z + energy
Energy conversions
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Cell takes PE of chemicals (in
electrons/bonds) and eventually converts
them to cellular work (KE)
Endergonic/exergonic reactions are usually
coupled so that the energy can either be
used immediately or stored (ATP) for later
use
Metabolism
The sum total of all chemical
reactions & physical workings
occurring in a cell
2 types of metabolism
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_________________ - biosynthesis
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building complex molecules from simple ones
requires energy (ATP) - endergonic
_________________ - degradation
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breaking down complex molecules into simple ones
generates energy (stored as ATP) - exergonic
Example - glycolysis
Enzymes
Needed to keep pace (speed up reactions)
 Reaction involves either breaking a molecule
apart or brining one together
 Catalyze reactions without becoming
products or being consumed in the reaction
 Act upon ______________ to form
_________________
 Lower _________________ so reaction rate
increases
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Enzyme-substrate interactions – lock and key fit
Active site
“Induced fit”
Enzyme - structure
Simple enzymes – consist of protein alone
 Conjugated enzymes or holoenzymes –
contain protein and nonprotein molecules
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apoenzyme –protein portion
cofactors – nonprotein portion
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metallic cofactors – iron, copper, magnesium
coenzymes - organic molecules - vitamins
How enzymes work: example - sucrase
Role of
coenzyme:
Transfer
functional group
from one
substrate to
another
Control of enzyme activity
1.
2.
_________________ inhibition –
substance that resembles normal substrate
competes with substrate for active site
_________________ inhibition – enzymes
are regulated by the binding of molecules
other than the substrate on the active site
•
•
Enzyme _____________– inhibits at the genetic
level by controlling synthesis of key enzymes
Enzyme _____________– enzymes are made
only when suitable substrates are present
Enzyme repression
Enzyme induction
Things that affect enzymes
Temperature, pH, pressure
 Enzymes have optimal T and pH for
activity
 Can be denatured by extreme
temperatures or pH (changes protein
structure)
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Roles of enzymes: Pathogenesis
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Produced by pathogenic microbes--make
microbe a better pathogen (evade host
response, destroy host tissues)
Examples:
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Hemolytic enzymes (hemolysins)
Elastase, collagenase (destroy connective tissue)
Lecithinase C (destroys cells)
Penicillinase (inactivates penicillin – antibiotic
resistance)
Note: names end in -________
Types of enzymes (location, quantity)
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_______enzymes – transported extracellularly, where
they break down large food molecules or harmful
chemicals; cellulase, amylase, penicillinase
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________enzymes – retained intracellularly & function
there
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_________________– always present regardless of
substrate concentration (glycolysis enzymes)
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_________________– produced in presence of
substrate, prevents cell from wasting resources
Figure 8.6 Types of enzymes
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Figure 8.7 Constitutive and regulated enzymes
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Types of reactions catalyzed by
enzymes
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Synthesis or _________________ reactions –
_________________ reactions to form covalent
bonds between smaller substrate molecules,
require ATP, release one molecule of water for
each bond
_________________ reactions–
_________________ reactions that break down
substrates into small molecules, requires the
input of water
Figure 8.8 Enzyme-catalyzed synthesis and
hydrolysis reactions
Transfer reactions by enzymes
1.
2.
3.
4.
5.
Aminotransferases – convert one type of amino acid
to another by transferring an amino group
Phosphotransferases – transfer phosphate groups,
involved in energy transfer
Methyltransferases – move methyl groups from one
molecule to another
Decarboxylases – remove carbon dioxide from
organic acids
Oxidation-reduction (redox)reactions – transfer
of electrons (may involve _________________ )
REDOX reactions
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The process by which electrons are transferred
between atoms is called an oxidation/reduction
reaction (redox) – we can track movement of e- by
following H transfers
_________________ = loses e- (donor becomes
oxidized; reducing agent)
_________________ = gains e- (acceptor
becomes reduced; oxidizing agent)
Occurs as a paired reaction
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“LEO says GER” or “OIL RIG”
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Cellular respiration is one big
redox reaction!
Redox reactions involve electron transfers
OILRIG
(Oxidation is Losing; Reduction is Gaining)
Redox reactions
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Involve electron transfers (energy transfers)
always occur in pairs
electron donor + electron acceptor = redox pair
process salvages electrons & their energy.
released energy can be captured to
_________________ ADP or another compound
Redox reactions
Electron donor + Electron acceptor
NOTE: electron transfers involve a hydrogen atom (proton + electron)
= ____________________ and involves an electron carrier
REMEMBER: Cellular respiration
is one big _________________ !
Metabolic Pathways
37
Electron carriers
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Redox reactions
resemble __________ that are loaded and
unloaded with electrons and hydrogen
most carriers are __________, NAD, FAD, NADP,
coenzyme A & compounds of the respiratory chain
donor
shuttle
acceptor
NAD reduction (carries 2 e- )
Redox reactions
Electron carriers – coupled reaction
Overview of cell respiration – electrons are removed from glucose and
eventually used to make ATP
_____________________________
NADH
1/
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The path
that
electrons
take on their
way down
from glucose
to oxygen
involves
many stops
(from food via NADH)
2 H
2 e
2
Energy for
synthesis
of
2 e
1/
2
H
2
Figure 6.6
ATP – the energy shuttle
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3 part molecule consisting of
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adenine – a nitrogenous base
ribose – a 5-carbon sugar
3 phosphate groups
_________________
_________________
_________________
How does ATP “give” energy?
ATP transfers energy to compounds that are going to be
catabolized (or going to do work) by donating the high
energy phosphate
_____________
of glucose by ATP
How is ATP regenerated?
ATP used for Energy must be
regenerated (ADP + Pi)
1.
2.
3.
substrate-level phosphorylation
oxidative phosphorylation
photophosphorylation
1. substrate-level phosphorylation
Other ways of making ATP
2. Oxidative phosphorylation: Used by
aerobes. series of redox reactions (electron
transport system). Involves chemiosmosis.
3. Photophosphorylation – used in
photosynthetic organsims. Driven by sunlight
(series of reactions).