From the molecules of life, to the
simpler organisms
Part
II
Paula B. Matheus Carnevali
Nutrient requirements
Over 95 % of cell dry weight is made up of:
• Carbon, oxygen, hydrogen, nitrogen, sulfur,
phosphorous, potassium, calcium, magnesium,
and iron.
Electron movement (electron transport chains,
oxidation-reduction reactions) provide energy
for use in work, and allow molecules’ reduction
during biosynthesis
Metabolisms
Carbon source
Autotrophs
CO2 sole or
Principal
biosynthetic
Carbon source
Energy source
Phototrophs
Light
Chemotrophs
Oxidation of organic
Or inorganic
compounds
Heterotrophs
Reduced, preformed,
Organic molecules
From other
organisms
Electron source
Lithotrophs
Reduced inorganic
molecules
Organotrophs
Organic molecules
Major nutritional types
Major nutritional types of microorganisms
From Prescott et al,, 2005
What is the energy needed for?
• Chemical work: involves the synthesis of
complex biological molecules from much
simpler precursors,
• Transport work: requires energy input in
order to take up nutrients, eliminate wastes,
and maintain ion balance,
• Mechanical work: energy is required to
change physical location of organisms, cells
and structures within the cells.
Light energy
Phototrophs (photosynthesis), Chemolitotrophs
Chemical energy
Carbon source for Chemoheterotrophs
Photolithoautotrophs and Chemolithoautotrophs
transform CO2 into biological molecules
Free-energy and Equilibrium
ΔG º’ = - 2.303 RT.logKeq
R is the gas constant
T is the absolute temperature
•When ΔG º’ is negative, K is greater than 1 and the
reaction goes to completion as written = exergonic reaction
•When ΔG º’ is positive, K is less than 1 and the reaction is
not favorable (little product will be formed at the equilibrium)
= endergonic reaction
Cells energy currency: ATP
Oxidation-reduction reactions
• Electron donor/Electron acceptor
• Equilibrium constant is the Standard
reduction potential (Eo) = measure of the
tendency of a donor to lose electrons
• Redox couples with more negative
reduction potentials will donate electrons
to couples with more positive potentials
and greater affinity for electrons.
When electrons
move from a donor
to an acceptor
with a more
positive redox
potential, free
energy is released
Electron movement and reduction potentials.
From Prescott et al., 2005
NAD: nicotinamide adenine dinucleotide
Electron movement requires the participation of carriers
to transport electrons between different locations
Photosynthesis
Photosynthetic organisms
capture light energy and use it
to move electrons from water
(and other electron donors) to
electron acceptors, such as
NADP+ , that have more
negative reduction potentials.
These electrons can flow back
to more positive acceptors and
provide energy for ATP
production.
Enzymes
Enzymes accelerate reactions by
lowering the activation energy
An overview of metabolism
Metabolism refers to the sum of the biochemical reactions required
for energy generation and the use of energy to synthesize cell material
from small molecules in the environment
Patterns of energy release
Fermentation the energy substrate is oxidized and degraded without the
participation of an exogenous or externally derived electron acceptor
Energy-yielding metabolism can make use of exogenous or externally
derived electron acceptors
• Metabolic pathways consist of enzymecatalyzed reactions arranged so that the
product of one reaction serves as a substrate
for the next.
• The uniqueness of microbial metabolism lies in
the diversity of the sources from which it
generates ATP and NADPH.
• Carbohydrates and other nutrients serve two
functions in the metabolism of heterotrophic
organisms: they are oxidized to release
energy, and supply carbon for the synthesis
of new cell constituents.
Glycolysis
Glucose + 2ADP
+ 2Pi + 2NAD+ →
2 Pyruvate +
2ATP + 2 NADH
+ 2H+
Fermentation
NADH produced in the
glycolytic pathway must be
oxidized back to NAD+
Pyruvate or one of its
derivatives can be used as an
electron and hydrogen
acceptor for the reoxidation
of NADH
This may lead to the
production of more ATP
A lot of
energy is
released
when
pyruvate is
degraded
aerobically
to CO2. The
substrate of
the Krebs
cycle is
acetyl-CoA
Electron transport chain
The electron
transport chain is
composed of a series
of electron carriers
that operate together
to transfer electrons
form donors, like
NADH and FADH2, to
acceptors, such as O2.
Electron transport at
these points may
generate proton and
electrical gradients.
Oxidative phosphorylation
the process by which the energy from electron
transport is used to make ATP
As many as three
ATP molecules may
be synthesized from
ADP and Pi when a
pair of electrons
pass from NADH to
an atom of O2
Anaerobic respiration
Not as efficient as aerobic respiration
•NO3- + 2e- + 2H+ → NO2- + H2O
(Dissimilatory nitrate reduction)
•2NO3- + 10e- + 12H+→ N2 + 6H2O
(Denitrification)
•SO42- + 8e- + 8H+ → S2- + 4H2O
Log number of viable cells
Bacterial Growth
Time
Microbial growth curve in a closed system. The growth of organisms
reproducing by binary fission can be plotted as the logarithm of the
number of viable cells versus the incubation time
The influence of environmental
factors on growth
Microbial responses to environmental factors
From Prescott et al,, 2005