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Chapter 27 - Bacteria and archaea. After studying this chapter you will be able to: Distinguish between the cell walls of gram-positive and gram-negative bacteria; state the function of the following features: capsule, fimbriae, sex pilus, nucleoid, plasmid, and endospore; explain how R plasmids confer antibiotic resistance on bacteria; explain the importance of/uses for prokaryotes. | Chapter 27 Bacteria and Archaea Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms. There are more prokaryotes in a handful of fertile soil than the number of people who have ever lived. They have an astonishing genetic diversity. Prokaryotes are divided into two domains: bacteria and archaea. Overview: Masters of Adaptation Why is this lakebed red? Figure 27.1 Why is this lakebed red? Concept 27.1: Structural and functional adaptations contribute to prokaryotic success Most prokaryotes are unicellular, although some species form colonies. Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryotic cells. Prokaryotic cells three most common shapes are spheres (cocci), rods (bacilli), and spirals. Prokaryotic Shapes (a) Spherical (cocci) 1 µm (b) Rod-shaped (bacilli) 2 µm (c) Spiral 5 µm Figure 27.2 The most common shapes of prokaryotes Prokaryotes Cell-Surface Structures An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment. Eukaryote cell walls are made of cellulose or chitin. Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides. Using the Gram stain, scientists classify many bacterial species into Gram-positive and Gram-negative groups based on cell wall composition. Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant. Many antibiotics target peptidoglycan and damage bacterial cell walls (often causing cell lysis). Bacteria: Cell Wall Composition: Gram Stain Cell wall Peptidoglycan layer Plasma membrane Protein Gram- positive bacteria Gram-positive: peptidoglycan traps crystal violet. Gram- negative bacteria (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. toxic bacteria 20 µm | Chapter 27 Bacteria and Archaea Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms. There are more prokaryotes in a handful of fertile soil than the number of people who have ever lived. They have an astonishing genetic diversity. Prokaryotes are divided into two domains: bacteria and archaea. Overview: Masters of Adaptation Why is this lakebed red? Figure 27.1 Why is this lakebed red? Concept 27.1: Structural and functional adaptations contribute to prokaryotic success Most prokaryotes are unicellular, although some species form colonies. Most prokaryotic cells are 0.5–5 µm, much smaller than the 10–100 µm of many eukaryotic cells. Prokaryotic cells three most common shapes are spheres (cocci), rods (bacilli), and spirals. Prokaryotic Shapes (a) Spherical (cocci) 1 µm (b) Rod-shaped (bacilli) 2 µm (c) Spiral 5 µm Figure 27.2 The most common shapes of prokaryotes Prokaryotes Cell-Surface Structures An important feature of .
