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Overview Lecture of Metabolism
BBOM 11e Sec. 2.4
Review Energy and Redox Reactions
BBOM 11e Sec. 5.4-5.8
Fermentation
BBOM 11e Sec. 5.9-5.10, 17.19-17.20 (Appendix I)
Quiz #1 Lectures 1-7
Overview of Metabolism
Resources from environment or growth medium BIOSYNTHESIS
Energy Sources:
Chemicals Light
Catabolism:
All reactions in the cell leading to Energy (ATP) production
Anabolism:
All biosynthetic (ATP-consuming) reactions Cellular and Population Growth Cellular and Population Growth Waste Products (End Products) :
Acids Alcohols CO2 H2O, ...
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Classes of Microorganisms Based on Source of Energy
Microbes can get energy for growth from many different sources
Source
Light Chemical Organic Inorganic
Class
Phototroph Chemotroph Chemoorganotroph Chemolithotroph
Read: BBOM 11e Sec 2.4
Redox Reactions
The Electron Tower:
Gives reduction potentials of redox couples
The Electron Tower and Redox Reactions
Living cells harvest energy from coupled Oxidation and Reduction electron transfer half-reactions. e- DONOR
H2
2H+ + 2e- (Oxidation)
e- ACCEPTOR
(Reduction) 2H+ + 2e- + O2
H2O
Eo'
1.24V
(Overall Rnx) H2 + O2 => H2O
Free Energy Yield
See BBOM 11e Appendix I
G'o = -nF Eo' = -2 x 96.48 kJ/V x 1.24 V = -239.27 kJ /mol
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Electron Carriers NAD and NADP
Redox Coenzymes
NAD
2H+ + 2e-
Intermediate electron carriers that transfer electrons from an electron donor to an electron acceptor
Nicotinamide Adenine Dinucleotide
NAD is used mostly in Catabolic pathways NAD+ +2e- +2H+ NADH +H+ NADP is used mostly in Anabolic pathways NADP+ +2e- + 2H+ NADPH +H+
NADP
ATP and Other "High Energy" Compounds
BBOM 11e Sec. 5.8, Fig. 5.12
PEP
Anhydride bonds with high free energies of hydrolysis
ATP
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What is Fermentation ?
BBOM 11e Sec. 5.9-5.10
An anaerobic catabolic process Internally balanced redox reactions An organic molecule serves as both the primary electron donor and final electron acceptor Energy captured as ATP formed by substrate-level phosphorylation Fermentation pathways are named for their initial substrate or waste products
SLP
(e.g. Glucose, Ethanol, Lactic acid)
Many U$eful Wa$te Product$
Glycolysis
Read: BBOM 11e Sec. 5.10
A common pathway in the fermentation (and respiration) of glucose. Glucose is converted by a series of (10 or 11) enzymatic steps (in 3 stages) to a variety of end products. Energy in the glucose molecule is converted to ATP by SLP e.g. Glucose 2ATP + Ethanol + CO2 or Lactic acid A.k.a The Embden-Meyerhof-Parnas (EMP) Pathway
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Three Stages of Glycolysis
BBOM 11e Sec.5.10, Fig. 5.14
Glucose is converted toactivated and split is first a variety of end products then oxidized to pyruvate Finally, pyruvate is reduced to a variety of fermentation waste 1. products
Stage Preparatory reactions: Glucose (6C) is split into 2 3C-units, 2 ATP consumed Stage 2. Oxidation: 2 NAD+ used to oxidize the 2 3C units, forming 4 ATP by SLP + 2 NADH and 2 pyruvate Stage 3. Reduction: 2 pyruvates reduced by 2 NADH forming waste products, there by oxidizing the 2NADH to regenerate 2NAD+
X2
Substrate-level Phosphorylation (in Glycolysis)
BBOM 11e Sec. 5.9
ATP synthesis by direct transfer of a "high energy" phosphate group from a phosphorylated (activated) organic compound to ADP
SLP in Stage 2 of Glycolysis
PEP (Phosphoenolpyruvate)
SLP
Pyruvate
Important to note: Electrons are transferred to NAD+ in an oxidationreduction step that precedes SLP
ATP synthesis occurs by SLP at two specific enzymatic steps in Glycolysis
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Energy Efficiency of Glycolysis (in Fermentations)
See BBOM 11e Fig. 5.14 & Appendix I
1. 2.
3.
4. X2
Efficiency = Energy in ATP / Free energy of the rnx X 100 Efficiency of the Ethanol-CO2 fermentation = 2 X -31.8 / -238.8 X 100 = 27%
Take a moment to think about Metabolic Efficiency
Fermentation reaction are not very efficient. A large amount of energy is lost . For example in the ethanol fermentation just discussed, only 27% of the free energy in a glucose molecule is captured as ATP, 73% is lost!!
Where does the lost energy go? Answer: Heat
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Summary
Metabolism is a life process by which energy sources (light or chemicals) and nutrients from the environment are used by cells to grow (reproduce) and produce waste products. The intermediate reactions of metabolism can be divided into catabolism (energy-capturing reactions) and anabolism (biosynthetic reactions). As described for carbon source above, microorganisms are also classified based on their energy source. Oxidationreduction reactions and the electron tower are fundamental chemistry concepts that aid in understanding metabolism. Knowledge of intermediate electron carriers and high energy compounds is also basic to understanding how metabolic processes conserve energy. Fermentation is an anaerobic catabolic process with internally balanced redox reactions in which an organic molecule serves as both the electron donor and the electron acceptor. Glycolysis is a common pathway for the fermentation of glucose. In glycolysis, glucose is converted by a series of enzymatic steps to a variety of waste products in three stages( preparatory, oxidation, reduction reactions). In these stages, glucose is activated and split, then oxidized to pyruvate, and finally reduced to waste products. Glycolysis is a relatively in efficient process resulting in the capture of only about 27% of the free energy in the glucose molecule. The rest of of the energy is lost as heat.
Quiz Time!!
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