Chapter Checkpoints
These are some important ideas you are learning in Chapter 8:

The Metabolism of Microbes
Metabolism includes all the biochemical reactions which occur in the cell. It is a cyclical, self-regulating complex of interdependent processes which encompasses many thousands of chemical reactions.

Anabolism is the energy-requiring subset of metabolic reactions, which synthesize large molecules from smaller ones.

Catabolism is the energy-releasing subset of metabolic reactions, which degrade or break down large molecules into smaller ones.

Enzymes are proteins which catalyze all biochemical reactions by forming enzyme-substrate complexes. The physical distortion of the substrate by an enzyme makes possible both bond-forming and bond-breaking reactions, depending on the pathway involved.

Enzymes are classified by the kinds of reactions they catalyze.

To function effectively, enzymes require highly specific conditions of temperature, pH, and osmotic pressure.

Enzyme production is regulated by processes of induction and repression, which, in turn, respond to availability of substrate and concentration of end products.

The Pursuit and Utilization of Energy
All metabolic processes require the constant input and expenditure of some form of usable energy. Chemical energy is the currency that runs the metabolic processes of the cell, but many forms of energy are involved in cell metabolism.

Chemical energy is obtained from the electrons of nutrient molecules through catabolism. It is used to perform the cell ``work'' of biosynthesis, movement, membrane transport, and growth.

Energy is extracted form nutrient molecules by redox reactions. A redox pair of substances passes electron and hydrogens between them. The donor substance loses electrons, becoming oxidized. The acceptor substance gains electrons, becoming reduced.

ATP is the energy molecule of the cell. It donates free energy to anabolic reactions and is continuously regenerated by three phosphorylation processes: substrate phosphorylation, oxidative phosphorylation, and (in certain organisms) photophosphorylation.

Pathways of Bioenergetics
Bioenergetics describes metabolism in terms of production, utilization, and transfer of energy by cells.

Catabolic pathways release energy through three pathways: glycolysis, the tricarboxylic acid cycle, and the respiratory transport system.

Cellular respiration is described by the nature of the final hydrogen acceptor. Aerobic respiration implies that O₂ is the final hydrogen acceptor. Anaerobic respiration implies that some other molecule is the final hydrogen acceptor. If the final hydrogen acceptor is an organic molecule, the anaerobic process is further described as fermentation.

Carbohydrates are preferred cell energy sources because they are superior hydrogen (electron) donors.

Glycolysis is the catabolic process by which glucose is oxidized into two molecules of pyruvic acid, with a net gain of 2 ATP. This process is also called substrate phosphorylation.

The tricarboxylic acid cycle converts the 3C pyruvic acid to 3 CO₂ molecules and transfers its hydrogens to redox carriers for energy harvesting.

The electron transport chain generates free energy through sequential redox reactions collectively called oxidative phosphorylation. This energy is used to regenerate up to 36 ATP for each glucose molecule catabolized.

Biosynthesis and the Crossing Pathways of Metabolism
Intermediary metabolism'' refers to the metabolic pathways which connect anabolic and catabolic reactions.

Amphibolic compounds are the ``crossroads compounds'' of intermediary metabolism. They not only participate in catabolic pathways, but also are precursor molecules to biosynthetic pathways.

Biosynthetic pathways utilize building block molecules from two sources: the environment and the cell's own catabolic pathways. Microorganisms construct macromolecules from these monomers using specialized enzymes particular to each species and ATP.

Proteins are essential macromolecules in all cells because they function as structural constituents, enzymes, and cell appendages.

Carbohydrates are crucial as energy sources, cell wall constituents, and components of nucleotides.

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