Cell Membranes and Intracellular Membranes

• The lipids of membranes are structured, diverse, fluid, and responsive to some environmental factors
• Proteins endow membranes with numerous functional capacities
• BOX 2.1 Protein Structure and the Bonds That Maintain It
• Carbohydrates play important roles in membranes

Epithelia

Elements of Metabolism

Enzyme Fundamentals

• Enzyme-catalyzed reactions exhibit hyperbolic or sigmoid kinetics
• Maximum reaction velocity is determined by the amount and catalytic effectiveness of an enzyme
• Enzyme–substrate affinity affects reaction velocity at the substrate concentrations that are usual in cells
• Enzymes undergo changes in molecular conformation and have specific binding sites that interact
• Enzymes catalyze reversible reactions in both directions
• Multiple molecular forms of enzymes occur at all levels of animal organization

Regulation of Cell Function by Enzymes

• The types and amounts of enzymes present depend on gene expression and enzyme degradation
• Modulation of existing enzyme molecules permits fast regulation of cell function

Evolution of Enzymes

Enzymes Are Instruments of Change in All Time Frames

The Life and Death of Proteins

Light and Color

• BOX 2.2 Squid and Bioluminescent Bacteria, a Study in Cross-Phylum Coordination: The Euprymna scolopes–Vibrio fischeri Symbiosis Margaret McFall-Ngai

Reception and Use of Signals by Cells

• Extracellular signals initiate their effects by binding to receptor proteins
• Cell signal transduction often entails sequences of amplifying effects
• Several second-messenger systems participate in cell signal transduction

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