Chapter 27 l Prokaryotes and the Origins of Metabolic Diversity

Overview: They’re (Almost) Everywhere! l Most prokaryotes are microscopic, but what they lack in size they make up for in numbers l There are more in a handful of fertile soil than the number of people who ever lived l Prokaryotes thrive almost everywhere, including places too acidic, too salty, too cold, or too hot for most other organisms l They have an astonishing genetic diversity

l Most prokaryotes are unicellular, although some species form colonies l Prokaryotic cells have a variety of shapes l The three most common of which are spheres (cocci), rods (bacilli), and spirals (spirilla). Concept 27.1: Structural, functional, and genetic adaptations contribute to prokaryotic success

LE 27-2 Spherical (cocci) Rod-shaped (bacilli) Spiral (spirilla) 5 µm2 µm1 µm

Cell-Surface Structures l 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 l Using the Gram stain, scientists classify many bacterial species into groups based on cell wall composition, Gram-positive and Gram- negative

Pepridoglycan layer Cell wall Protein Gram- positive bacteria Gram-positive Gram-negative Gram- negative bacteria Pepridoglycan layer Cell wall Plasma membrane Lipopolysaccharide Plasma membrane Protein Outer membrane 20 µm

l The cell wall of many prokaryotes is covered by a capsule, a sticky layer of polysaccharide or protein

LE 27-4 Capsule 200 nm

l Some prokaryotes have fimbriae and pili, which allow them to stick to their substrate or other individuals in a colony

LE 27-5 Fimbriae 200 nm

Motility l Most motile bacteria propel themselves by flagella that are structurally and functionally different from eukaryotic flagella l In a heterogeneous environment, many bacteria exhibit taxis, the ability to move toward or away from certain stimuli

LE 27-6 Flagellum Filament Cell wall Hook Basal apparatus Plasma membrane 50 nm

Internal and Genomic Organization l Prokaryotic cells usually lack complex compartmentalization l Some prokaryotes do have specialized membranes that perform metabolic functions

LE 27-7 Thylakoid membranes Respiratory membrane Photosynthetic prokaryote Aerobic prokaryote 0.2 µm 1 µm

l The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region

LE 27-8 Chromosome 1 µm

Classification l Domain: Bacteria l Domain: Archaea l Kingdom: “Monera?” l Shape cocci (sphere) bacilli (rod) helical (spiral)

Structural characteristics l Cell wall~ peptidoglycan (sugars & proteins); l √ Gram +: w/peptidoglycan penicillin action l √ Gram -: little peptidoglycan, lipopolysaccharides; most pathogens; impede drug action l Capsule: adherence; protection l Pili: adherence; conjugation

Motility l 1- Flagella l 2- Helical shape (spirochetes) l 3- Slime l 4-Taxis (movement away or toward a stimulus)

Form & Function l Nucleoid region (genophore: non-eukaryotic chromosome) l Plasmids l Asexual reproduction: binary fission (not mitosis) “Sexual” reproduction (not meiosis): 1.transformation~ uptake of genes from surrounding environment 2.conjugation ~ direct gene transfer from one prokaryote to another 3.transduction~ gene transfer by viruses l Endospore: resistant cells for harsh conditions (250 million years!)

Nutrition & Metabolism l Photoautotrophs: photosynthetic; harness light to drive the synthesis of organics (cyanobacteria) l Chemoautotrophs: oxidation of inorganics for energy; get carbon from CO2 l Photoheterotrophs: use light to generate ATP but get carbon in an organic form l Chemoheterotrophs: consume organic molecules for both energy and carbon saprobes- dead organic matter decomposers parasites- absorb nutrients from living hosts l Nitrogen fixation: conversion of atmospheric nitrogen (N2) to ammonium (NH4+) l Oxygen relationships: obligate aerobes; facultative anaerobes; obligate anaerobes

Prokaryotic ecology l Decomposers: unlock organics from corpses and waste products l Symbiosis~ symbiont/host mutualism (+, +) parasitism (+, -) commensalism (+, 0) l Disease opportunistic: normal residents of host; cause illness when defenses are weakened Koch’s postulates: criteria for bacterial disease confirmation exotoxins: bacterial proteins that can produce disease w/o the prokaryote present (botulism) endotoxins: components of gram - membranes (Salmonella)