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Summary Metabolism - energy classes and bioenergetics
- Instelling
- Rijksuniversiteit Groningen (RuG)
Summary about lecture and corresponding literature about Metabolism - energy classes and bioenergetics.
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HC1 Metabolism I – Energyclasses & Bioenergetics (BOOK)
Chapter 3.2-3.7
CH3 Microbial Metabolism
3.2 Transporting nutrients into the cell
Active transport can be done by three basic mechanisms:
- Simple transport (one transmembrane protein)
- Group translocation (series of proteins) PROKAYOTES ONLY
- ABC transport (three components:)
o Substrate binding protein
o Transmembrane receptor
o ATP-hydrolysing enzyme
There are two major reactions that catalyse transport events. Symport reactions (solute and proton
are cotransported in one direction) and antiport reactions (solute and proton are transported in
opposite direction).
There are two important differences between simple transport and group translocation:
- In group translocation the transported substance is chemically modified during the transport
process
- Energy rich organic compounds drive the transport process
In the phosphotransferase system, five enzymes work together to phosphorylates sugars for
transport into the cell. This process is driven by energy from phosphoenolpyruvate.
Gram-negative bacteria are bacteria that contain a periplasm (lies between cytoplasmic membrane
and outer membrane) and is home to many proteins involved in transport.
3.3 Energy classes of
microorganisms
Chemotrophs are organisms that conserve
energy from chemicals and
chemoorganotrophs use organic chemicals.
Chemilithotrophy is tapping energy available
from the oxidation of inorganic compounds by
chemolithotrophs.
Phototrophs can convert light energy to ATP
and do alsno not require chemicals as a source
of energy. There are two forms of
phototrophy, oxygenic photosynthesis (O2 is
produced) and anoxygenic photosynthesis (no
O2 produced).
Heterotrophs (chemoorganotrophs) obtain
cell carbon from organic compounds,
autotrophs (chemolithotrophs and
phototorphs) use CO2 as their carbon source.
, 3.4 Principles of bioenergetics
Free energy is the energy available to do work. dG0’ is the change in free energy during a reaction. If
dG0’ is negative, the reaction is said to be exergonic (release energy) and if dG0’ is positive, the
reaction is said to be endergonic (require energy).
The Gf0 is the free energy of formation and is the energy released or required during the formation
of a given molecule from elements.
Endergonic; Gf0 is positive, exergonic: Gf0 is negative.
If A + B —> C + D then dG0’ = Gf0[C + D] - Gf0[A + B]
dG is the free-energy change that occurs under the actual
conditions in twhich the organisms is growing.
dG = dG0’ + RT x ln(Keq)
R and T are physical constants
Keq is the equilibrium constant for the reaction = ([C][D]/[A]
[B])
3.5 Catalysis and enzymes
The activation energy is the minimum energy required for a chemical reaction to begin. Catalysts are
substances that facilitates a reaction but is not consumed by it. The major catalysts in cells are
enzymes which combine with the substrate and form an enzyme-substrate complex. Then, as the
reaction proceeds, the product is released and the enzymes is returned to its original state. Many
enzymes contain small molecules that participate in catalysis but are not substrates this can be either
prosthetic groups (bind tightly to enzymes) or coenzymes (loosely bound —> may associate with a
number of different enzymes).
Enzymes that catalyse highly exergonic or highly endergonic reactions, typically function in one
direction.
3.6 Electron donors and acceptors
Oxidation is the removal of an electron and reduction is the addition of an electron. An oxidation +
reduction is called a redox reaction. Oxidation is also one part of the redox reaction (half reaction)
and reduction is the other part (second half reaction).
The substance oxidised is an electron donor and the substance reduced is an electron acceptor.
A redox couple consists of the oxidised form the couple (on the left) and the reduced form (on the
right): H2 ↔ 2H+ + 2e-
The tendency to donate or accept electron differ between substances and is called the reduction
potential (E0’ for standard conditions). Substances whose E 0’ is more negative donate electrons to
substances whose E0’ is more positive.
dE0’ is proportional to dG0’ : Nernst equation - dG0’ = -n x F x dE0’
In which n is the number of electrons transferred and F is the Faraday constant (96.5 kJ/V)
NAD+ and NADH form a redox couple and function as coenzymes.
3.7 Energy-rich compounds
Energy conservation in cells is through the formation of compounds containing energy-rich phosphor
(linked by either ester or anhydride bonds) or sulfur bonds. Cells typically use compounds whose dG 0’
of phosphate hydrolyses exceeds -30 kJ/mol.
The most important energy-rich phosphate compound in cells is adenosine triphosphate (ATP) —>
-32 kJ/mol.
Coenzyme A are compounds that can be hydrolysed for the use of free energy. The energy released
in the hydrolysis of coenzyme A is conserved in the synthesis of ATP.
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