6: Fueling and Building Cells
- Page ID
- 42511
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Chapter 6 BIOL 235 Learning Outcomes
- Identify the two types of metabolic process by which chemoheterotrophs obtain energy
- Explain why a terminal electron acceptor is necessary for energy-generating metabolic processes (respiration or fermentation).
- Distinguish between the two mechanisms (__________ phosphorylation and _____________ phosphorylation) by which ATP is formed in cells.
- Differentiate between fermentation and respiration based on the following questions:
- Is it always, sometimes, or never an anaerobic process?
- By what mechanism is ATP formed (substrate-level, oxidative)?
- Is the terminal electron acceptor always, sometimes, or never organic?
- Is an electron transport chain used to generate energy?
- Compare the amount of ATP produced from glucose by aerobic respiration, anaerobic respiration, and fermentation (see Table 6.2.1) (most, in between, or least; don't worry about exact numbers).
- Given a metabolic pathway, determine if it is a usable fermentation pathway based on 1) does it produce a net gain of ATP and 2) are all NADH re-oxidized to NAD+.
- If given an energy-generating metabolic process (either described or in a figure), determine whether it is fermentation, aerobic respiration, or anaerobic respiration.
- Sketch the processes of lactic acid fermentation and respiration (general, including cellular location).
- Identify common products of bacterial fermentations, including the kind of molecule always produced in bacterial fermentations.
- Explain how oxidation/reduction of electron carriers can be linked to pumping of protons across a membrane.
- Explain where the electrons for the electron transport chain come from in an organism using glucose as an energy source and on what molecule those electrons are carried. Consider both the original chemical source of the electrons and the metabolic pathways that harvest those electrons.
- Define proton motive force and explain why it is necessary for ATP synthesis through respiration.
- Describe the generation of ATP by ATP synthase (oxidative phosphorylation).
- Identify the main difference between aerobic and anaerobic respiration.
- Describe how the metabolites of glycolysis and the Krebs (TCA) cycle can be used by the cell for purposes other than energy generation
- Describe the biosynthesis of amino acids by both amination and transamination
- Explain nitrogen fixation, how it differs from the way most organisms obtain nitrogen for their cells, and what domain of organisms nitrogen fixation is limited to.
- Give one example of a nitrogen fixer and explain its direct role in food production.
As discussed in Chapter 4, all organisms require both carbon (the cell's main building material) and energy (to build the cell's structures and perform other metabolic functions). Although microbes can use either organic carbon (heterotrophs) or carbon dioxide (autotrophs) for carbon and light (phototrophs) or chemical energy (chemotrophs), all pathogens are chemoheterotrophs. The host which they are infecting is their source of both carbon and energy. Most microbes used for food production are also chemoheterotrophs. Therefore, we will focus on how chemoheterotrophs fuel and build their cells.
Chemoheterotrophs can generate ATP from organic molecules using two different mechanisms: respiration and fermentation. In both mechanisms, the electrons stored on NADH in the metabolic reactions of Central Metabolism are "dumped" on a final electron acceptor, thus regenerating NAD+ to be used again in Central Metabolism. In respiration, the transfer of electrons from NADH to the final electron acceptor (obtained from the environment) occurs via an electron transport chain (ETC). The ETC concurrently creates a proton gradient which is used by ATP synthase to generate ATP through oxidative phosphorylation. In fermentation, however, the transfer of electrons from NADH to the final electron acceptor (a metabolite formed within the cell) does not generate ATP in addition to that already produced by substrate-level phosphorylation.
The precursor metabolites generated through Central Metabolism are used to build the important molecules (and eventually structures) of the cell in anabolic pathways. Sometimes additional macronutrients are required to build the molecules of the cell, which cells acquire in various ways. For example, amino acids require nitrogen for their amino group. Although there are hundreds of critical anabolic pathways in cells, the acquisition of nitrogen and synthesis of amino acids will be used as an example of anabolism in bacteria.
- 6.1: Respiration
- This page covers the electron transport system (ETS) in both prokaryotic and eukaryotic cells, detailing its role in aerobic and anaerobic respiration. It explains oxidative versus substrate-level phosphorylation, emphasizing the generation of a proton motive force (PMF) and ATP production via ATP synthase. The maximum ATP yield from aerobic respiration (up to 38 ATP) is highlighted, alongside variations in ATP yield in anaerobic processes and their importance for microbial diagnostics.
- 6.2: Fermentation
- This page discusses fermentation as an anaerobic process for ATP production, contrasting it with respiration. It details major fermentation pathways (e.g., lactic acid and alcoholic fermentation) and their key microorganisms, highlighting their importance in food production, probiotics, and commercial uses.
- 6.3: Catabolism of Lipids and Proteins
- This page covers lipid and protein catabolism in microbes, emphasizing their roles in energy production and microbial identification. It details the breakdown of triglycerides and phospholipids, aided by specific enzymes, and the integration of glycerol and fatty acids into glycolysis and the Krebs cycle via β-oxidation. Additionally, it discusses protein catabolism through extracellular proteases, helping to identify bacteria based on enzyme production.
- 6.4: Photosynthesis and the Importance of Light
- This page provides an overview of photosynthesis, detailing both microbial processes and the stages involved. It describes light-dependent and light-independent reactions, with a focus on the Calvin-Benson cycle. Key elements include chloroplasts in eukaryotes and infolded plasma membranes in prokaryotes, the organization of photosynthetic pigments into photosystems, and the roles of RuBisCO, ATP, and NADPH in carbon fixation and glucose synthesis.
- 6.5: Biogeochemical Cycles
- This page highlights the essential roles of microorganisms in biogeochemical cycles—carbon, nitrogen, and sulfur—addressing their functions in converting and recycling nutrients. It details bioremediation techniques, including in situ and ex situ methods for pollutant cleanup, and discusses enhanced bioremediation strategies. Overall, the page emphasizes how microbes contribute to environmental health and restoration through their natural degradation processes.
- 6.6: Anabolism
- This page explores anabolic pathways, focusing on the biosynthesis of cellular molecules from simpler compounds using precursor metabolites, ATP, and electrons. It explains the link between catabolic and anabolic processes in amino acid biosynthesis, detailing nitrogen assimilation via transamination and amination.
Thumbnail: "Making Traditionally Fermented Pickles" by Chiot's Run is licensed under CC BY-NC 2.0