From the molecules of life, to the simpler organisms Paula B. Matheus Carnevali Part II

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 Autotrophs CO 2 sole or Principal biosynthetic Carbon source Heterotrophs Reduced, preformed, Organic molecules From other organisms Carbon sourceEnergy source Chemotrophs Oxidation of organic Or inorganic compounds Organotrophs Organic molecules Lithotrophs Reduced inorganic molecules Phototrophs Light Electron source

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 Photolithoautotrophs and Chemolithoautotrophs transform CO 2 into biological molecules Carbon source for Chemoheterotrophs

Free-energy and Equilibrium ΔG º’ = 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.

Electron movement and reduction potentials. From Prescott et al., 2005 When electrons move from a donor to an acceptor with a more positive redox potential, free energy is released

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 enzyme- catalyzed 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 CO 2. 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 FADH 2, to acceptors, such as O 2. 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 O 2

Anaerobic respiration Not as efficient as aerobic respiration NO e - + 2H + → NO H 2 O (Dissimilatory nitrate reduction) 2NO e H + → N 2 + 6H 2 O (Denitrification) SO e - + 8H + → S H 2 O

Bacterial Growth 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 Log number of viable cells Time

Microbial responses to environmental factors From Prescott et al,, 2005 The influence of environmental factors on growth