Unit Two - Bacterial Metabolism
Energy (ATP) Production Mechanisms - Eukaryotes
- Ethanol fermentation
- Lactic fermentation
- Aerobic respiration
- Oxygenic photosynthesis
Energy Production Mechanisms Not Found in Eukaryotes
- Unique fermentations proceeding thru the Embden-Meyerhof pathway
- Other fermentation pathways such as the phosphoketolase and Entner-Doudoroff pathways
- Anaerobic respiration: respiration that uses substance other than 02 as a final e- acceptor
- Lithotrophy: use of inorganic substances as sources of energy
- Photoheterotrophy: use inorganic compounds as C sources during bacterial photosynthesis
- Anoxygenic photosynthesis: photophosphorylation in the absence of O2
- In addition, among autotrophic prokaryotes, there are 3 ways to fix CO2, 2 of which are unknown among eukaryotes, the CODH (acetyl CoA pathway) & the reverse TCA cycle
Metabolic Versatility - E. coli
- Fermentation
- Respiration - aerobic, or anaerobic using NO3 or fumurate
- Glucose or lactose - sole C source for growth
Metabolic Versatility - Rhodospirillum rubrum
- all the heterotrophic capabilities as E. coli
- + photoautotrophy
- photoheterotrophy
- lithotrophy
A. Energy
1. Thermodynamics - storage, transformation, & dissipation of energy - energy differences btwn initial and final state
a. First Law
Energy can neither be created nor destroyed
b. Second Law
As energy is transferred, total amount of entropy (disorder) increases
2. Free Energy (delta G - DG)
- All chem rxns can be described by the following equation:
D
G = DH - TDS - measures the energy change for any system
D
G - amt of energy available to do work
D
H - total energy of rxn
T - absolute temperature in degrees Kelvin
D
S - amt of energy that is lost to disordering the system & is not available for work (entropy)
- Making S (entropy) larger results in disordering of the system --> a neg.
DG
- So rxns that result in a large amount of disorder are favorable & result in a neg.
DG
Some examples:
1.fermentation: glc à pyruvate; DG= -57kcal/mol
2.respiration: pyruvate à CO2 + H2O; DG = -633
- A decrease in S results from an ordering of a system & a pos
DG
Q. What's the bottom line here?
A. If rxns have neg.
DG values, they can release energy, they can happen spontaneously.
If needed rxns have pos.
DG values, they're not going to happen.
3. Oxidation-Reduction Reactions (Redox rxns)
- Redox rxns are often associated w/energy transfer in cells
- oxygen rarely involved
- oxidation rxn always coupled w/a reduction rxn
- Definitions: loss of e- = Oxidation
gain of e- = Reduction
Mnemonic: LEO says GER
e- donor - reducing agent
e-acceptor - oxidizing agent
- Ex. Oxidation (e- losing) rxn:
1. Fe++ - e-
à Fe+++
2. H2 - 2e-
à 2H+
Ex. Reduction (e- gaining) rxn:
1. 1/2 O2 + 2e- + 2H+
à H2O
- All molecules contain e- as part of the atoms that make them up
- Each molecule has a potential to donate & accept e- from another molecule
- In chemistry this is written as a redox couple
Ex.
2H+/H2
1/2 O2/H2O
- Redox couples with more neg reduction potentials will donate e- to Redox couples w/ more pos potentials.
For example:
NAD+ + 2H+ + 2e-
à NADH + H+ -0.32
1/2O2 + 2H+ + 2e-
à H2O +0.82
NADH + H+ + 1/2O2
à NAD+ + H2O energy released
NAD+ + 2H+ + 2e- à NADH + H+
becomes
NADH + H+ à NAD+ + 2H+ + 2e-
Picture of redox tower
Summary
- Cells get their energy from the sun to drive energy requiring (thermodynamically unfavorable) rxns
- Many of their rxns involve oxidation/reduction couples
Q. What do cell use energy for?
A. 3 main activities
1. Synthesis of complex biological molecules
2. Transport
3. Movement
4. Energy Carriers
- Nicotinamide Adenine Dinucleotide (NAD+)
- Nicotinamide Adenine Dinucleotide Phosphate (NADP+)
Structures of NAD oxidized and reduced
- Flavin adenine dinucleotide (FAD)
- Flavin mononucleotide (FMN)
- Coenzyme Q (CoQ) = ubiquinone
- Cytochromes
- Non heme proteins
Structures of FAD and heme
5. High Energy Compounds
- Phosphoenolpyruvate (PEP)
- Adenosine Tri Phosphate (ATP)
Structure of ATP
To pull it all together:
- the energy in chem or light is extracted by running a series of rxns that eventually deposit bond energy & high energy e- in ATP & NAD(P)H
- this stored up energy then drives other rxns that help the cell grow & reproduce
H2O - 2e-
à 2H+ + 1/2O2
NADP+ + 2e-
à NADPH + H+
CO2
à glucose (energized, lots of e-)
Glucose
à CO2 + H2O lots e- released
energy stored as ATP
Q. but what catalyzes, controls, & coordinates all these rxns?
A. Enzymes!