chapter 2 bacterial classification, structure, and replication
TRANSCRIPT
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Chapter 2.- Bacterial Classification, Structure, and Replication
Processes of Life
• Growth
• Reproduction
• Responsiveness
• Metabolism
Examples of types of cells
Figure 3.1
Prokaryotic and Eukaryotic Cells: An Overview
• Prokaryotes
– Lack nucleus
– Lack various internal structures bound with phospholipid membranes
– Are small, ~1.0 µm in diameter
– Have a simple structure
– Composed of bacteria and archaea
Typical prokaryotic cell
Figure 3.2
Prokaryotic and Eukaryotic Cells: An Overview
• Eukaryotes
– Have nucleus
– Have internal membrane-bound organelles
– Are larger, 10–100 µm in diameter
– Have more complex structure
– Composed of algae, protozoa, fungi, animals, and plants
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Typical eukaryotic cell
Figure 3.3
Approximate size of various types of cells
Figure 3.4
General Characteristics of Prokaryotic Organisms
• Prokaryotes
– Most diverse group of cellular microbes
– Habitats
• From Antarctic glaciers to thermal hot springs
• From colons of animals to cytoplasm of other prokaryotes
• From distilled water to supersaturated brine
• From disinfectant solutions to basalt rocks
– Only a few capable of colonizing humans and causing disease
Typical prokaryotic morphologies
Figure 11.1
General Characteristics of Prokaryotic Organisms
• Arrangement of Prokaryotic Cells
– Result from two aspects of division during binary fission
• Planes in which cells divide
• Separation of daughter cells
Arrangements of cocci
Figure 11.6
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Arrangements of bacilli
Figure 11.7
Bacterial shapes and arrangements
Figure 3.12
External Structures of Bacterial Cells
• Glycocalyces
– Gelatinous, sticky substance surrounding the outside of the cell
– Composed of polysaccharides, polypeptides, or both
External Structures of Bacterial Cells
• Two Types of Glycocalyces
– Capsule
• Composed of organized repeating units of organic chemicals
• Firmly attached to cell surface
• May prevent bacteria from being recognized by host
– Slime layer
• Loosely attached to cell surface
• Water soluble
• Sticky layer allows prokaryotes to attach to surfaces
Example of Capsule
Figure 4.20
Glycocalyces
Figure 3.5
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External Structures of Bacterial Cells
Animation: Motility
External Structures of Bacterial Cells
• Flagella
– Are responsible for movement
– Have long structures that extend beyond cell surface
– Are not present on all bacteria
External Structures of Bacterial Cells
• Flagella
– Structure
• Composed of filament, hook, and basal body
• Basal body anchors filament and hook to cell wall by a rod and a series of either two or four rings of integral proteins
External Structures of Prokaryotic Cells
Animation: Flagella: Structure
Proximal structure of bacterial flagella
Figure 3.6
Basic arrangements of bacterial flagella
Figure 3.7
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External Structures of Bacterial Cells
Animation: Flagella: Arrangement
External Structures of Bacterial Cells
Animation: Flagella: Spirochetes
Axial filament
Figure 3.8
External Structures of Bacterial Cells
• Flagella
– Function
• Rotation propels bacterium through environment
• Rotation reversible; can be counterclockwise or clockwise
• Bacteria move in response to stimuli (taxis)– Runs
– Tumbles
Motion of a peritrichous bacterium
Figure 3.9
External Structures of Bacterial Cells
Animation: Flagella: Movement
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External Structures of Bacterial Cells
• Fimbriae and Pili
– Rod-like proteinaceous extensions
External Structures of Bacterial Cells
• Fimbriae
• Sticky, bristlelike projections
• Used by bacteria to adhere to one another, to hosts, and to substances in environment
• Shorter than flagella
• Serve an important function in biofilms
Fimbriae
Figure 3.10
External Structures of Prokaryotic Cells
• Pili
– Tubules composed of pilin
– Also known as conjugation pili
– Longer than fimbriae but shorter than flagella
– Bacteria typically only have one or two per cell
– Mediate the transfer of DNA from one cell to another (conjugation)
Pilus
Figure 3.11
Bacterial Cell Walls
• Provide structure and shape and protect cell from osmotic forces
• Assist some cells in attaching to other cells or in resisting antimicrobial drugs
• Can target cell wall of bacteria with antibiotics• Give bacterial cells characteristic shapes• Composed of peptidoglycan• Scientists describe two basic types of bacterial cell
walls– Gram-positive and Gram-negative
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Comparison of structures of glucose, NAG, and NAM
Figure 3.13
Bacterial Cell Walls
• Gram-positive Bacterial Cell Walls
– Relatively thick layer of peptidoglycan
– Contain unique polyalcohols called teichoic acids
– Appear purple following Gram staining procedure
– Up to 60% mycolic acid in acid-fast bacteria helps cells survive desiccation
Gram-positive bacteria
Figure 3.15a
Prokaryotic Cell Walls
• Gram-Negative Bacterial Cell Walls
– Have only a thin layer of peptidoglycan
– Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS)
– May be impediment to the treatment of disease
– Appear pink following Gram staining procedure
Gram-negative bacteria
Figure 3.15b
Gram Staining
Gram +Gram -
Figure 4.17
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Acid-fast Cells
• Gram positive cells
• Extra stuff in cell wall– Mycolic acid – a waxy lipid, up to 60% of cell wall
– Resistant to dessication, antibiotics
• Special staining procedure called acid-fast staining
• Mycobacteria
Acid-fast Staining
Figure 4.18
Bacteria without Cell Walls
• Mycoplasma
– Sterols in cell membrane
LPS
• Union of lipid with sugar
• Lipid portion known as lipid A
– Also known as endotoxin
– Dead cells release lipid A when cell wall disintegrates
– May trigger fever, vasodilation, inflammation, shock, and blood clotting
– Can be released when antimicrobial drugs kill bacteria
Periplasmic Space
• Located between outer membrane and cell membrane
– Contains peptidoglycan and periplasm
– Contains water, nutrients, and substances secreted by the cell, such as digestive enzymes and proteins involved in transport
Bacterial Cytoplasmic Membranes
• Structure– Referred to as phospholipid bilayer
• Composed of lipids and associated proteins
– Fluid mosaic model describes current understanding of membrane structure
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Structure of prokaryotic cytoplasmic membrane
Figure 3.16
Bacterial Cytoplasmic Membranes
• Function– Energy storage
– Harvest light energy in photosynthetic bacteria
– Selectively permeable
– Naturally impermeable to most substances
– Proteins allow substances to cross membrane
– Maintain concentration and electrical gradient
Electrical potential of a cytoplasmic membrane
Figure 3.17
Bacterial Cytoplasmic Membranes
• Function
– Passive processes
• Diffusion
• Facilitated diffusion
• Osmosis
Passive processes of movement
Figure 3.18
Osmosis
Figure 3.19
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Effects of solutions on cells
Figure 3.20
Prokaryotic Cytoplasmic Membranes
• Function
– Active processes
• Active transport
– Group translocation
• Substance chemically modified during transport
Mechanisms of active transport
Figure 3.21
Bacterial Cytoplasmic Membranes
Animation: Active Transport: Overview
Bacterial Cytoplasmic Membranes
Animation: Active Transport: Types
Group translocation
Figure 3.22
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Cytoplasm of Bacteria
• Cytosol
– Liquid portion of cytoplasm
• Inclusions
– May include reserve deposits of chemicals
• Endospores
– Unique structures produced by some bacteria that are a defensive strategy against unfavorable conditions
The formation of an endospore
Figure 3.24
General Characteristics of Prokaryotic Organisms
• Endospores– Produced by Gram-positive Bacillus and
Clostridium
– Each vegetative cell transforms into one endospore
– Each endospore germinates to form one vegetative cell
– Defensive strategy against unfavorable conditions
– Concern to food processors, health care professionals, and governments
Spore Structure
Outer Spore Coat(Exosporium)
Spore Coat
Outer Membrane
Cortex
Inner Membrane
Core
Spore Wall
Locations of endospores
Figure 11.8
Cytoplasm of Prokaryotes
• Nonmembranous Organelles
– Ribosomes
• Sites of protein synthesis
– Cytoskeleton
• Plays a role in forming the cell’s basic shape
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A simple helical cytoskeleton
Figure 3.25
General Characteristics of Prokaryotic Organisms
• Reproduction of Prokaryotic Cells
– All reproduce asexually
– Three main methods
• Binary fission (most common)
• Snapping division
• Budding
General Characteristics of Prokaryotic Organisms
Animation: Bacterial Growth: Overview
Binary fission
Figure 11.2
Snapping division, a variation of binary fission
Figure 11.3
Budding
Figure 11.5
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Nomenclature
• Genus– It is always a noun– It is written first– It is capitalized
• Species– It is usually an adjective– It is written second– It always contains lowercase letters
• Genus + species is printed in italics or underlined
• Example:– Escherichia coli, E. coli
The End
Chapter 2.- Bacterial Classification, Structure, and Replication