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BIO 205
Chapter 4
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Chlamydiae are extremely small, mostly pathogenic bacteria
Cyanobacteria carry out photosynthesis using chlorophyll,responsible for the appearance of oxygen in Earths earlyatmosphere
Actinobacteria include Streptomyces, the genus that produces theantibiotic streptomycin
Firmucutes consist of many gram-positive species, such asBacillus, Clostridium, Staphylococcus, and Streptococcus
Proteobacteria contain the largest and most diverse group ofspecies, including E. coliand many human pathogens
The majority of the 18 phyla ofBacteria play a positive role innature
The Domain Bacteria Contains Some of the Best Studied Prokaryotes
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Thermoacidophiles (grow athigh temperature with low
pH
Extreme halophiles (saltlovers)
Methanogens (live inanoxic environments)
Euryarchaeota contain:
The DomainArchaea ContainsMany Extremophiles
Crenarchaeota tend to grow inhot acidic environments suchas hot springs and volcanic
vents
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The Shapes and Arrangements of Prokaryotic Cells
Three Main Shapes:
Rod
Sphere
Spiral
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The Shapes and Arrangements of Prokaryotic Cells
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Streptococcus Chain
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Many cocci and some bacilli appear in groups or chains
A spherical bacterial cell is a coccus
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Spiral shaped bacteria can appear as vibrios (comma-shaped), spirilla (helical), or spirochete
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Prokaryotic Cell
Structure
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Pili
Pili help:
Pili Are Protein Fibers Extending from the Surfaceof Many Prokaryotes
Form biofilms andmicrocolonies.Some bacterialspecies have
conjugation pili,used to transfergenetic materialbetween cells
Attach cells to surfaces
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Prokaryoticflagella contain ahelical filament,a hook, and a
basal body
Flagella can be used for cell motility
Prokaryotic Flagella Are Long Appendages
Extending from the Cell Surface
Flagella
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Flagella Continued
Bacteria exhibit chemotaxis, moving up the concentrationgradient of a chemical attractant
Prokaryotic Flagella Are Long Appendages Extending fromthe Cell Surface
Some prokaryotes move without flagella by gliding across a
solid surface
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It protects cells from theenvironment, and allows them
to attach to surfaces
A thin diffuse layer ofpolysaccharides is a slime layer
A thick glycocalyx covalentlybound to the cell is a capsule
The glycocalyx is an adheringlayer of polysaccharides (andsometimes small proteins)
The Glycocalyx Is an Outer LayerExternal to the Cell Wall
Glycocalyx
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CapsuleCapsule in Acinetobacter species by negative staining
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Cell Envelope
The cell wall protectsthe cell from injury, andmaintains cell shapeand water balance
Cell Membrane
Cell Wall
The cell envelope iscomposed of two
parts:
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Prokaryotic Cell Wall
The outer membrane contains proteins called porinsthat selectively allow small molecules into the
periplasmic space
The gram-negative cell wall has an outer membrane,separated from the cell membrane by the periplasmic
space
Gram-negative bacteria have a two-dimensional
peptidoglycan layer and no teichoic acid
Gram-positive bacteria have thick peptidoglycan cellwalls containing teichoic acid
Cell walls in prokaryotes contain peptidoglycan
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The S-layer is the most common archaeal cell wall,consisting of protein or glycoprotein in a crystal lattice
Others have polysaccharides, proteins, or both
No archaea have peptidoglycan in the cell wall, but somehave pseudopeptidoglycan
The Archaeal Cell Wall Also Provides Mechanical Strength
Archaeal Cell Wall
P k ti C ll M b
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Prokaryotic Cell Membrane
Hydrophobic fatty acid chains in the phospholipids form a
permeability barrier
The phospholipid molecules are arranged in a bilayer
The cell membrane is a fluid layer of phospholipid and
protein (the fluid mosaic model)
The Cell Membrane Represents the Interface between theCell Environment and the Cell Cytoplasm
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molecule transport
sensation of stimuli
DNA replication
energy metabolism
cell wall synthesis
Membrane proteins perform or aid in many functions,such as:
Antimicrobial substances may disrupt or dissolve thebilayer
The Cell Membrane Represents the Interface between theCell Environment and the Cell Cytoplasm
Prokaryotic Cell Membrane
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Facilitated Diffusion
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Adjacent lipid tails are bound together forming a lipidmonolayer, instead of a bilayer
Fatty acids are usually absent
Hydrophobic lipid tails are attached to glyceroldifferently in archaea
The Archaeal Cell Membrane Differs from Bacterial andEukaryotic Membranes
Archaeal Cell Membranes
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The Cell Cytoplasm and Internal Structures
N l id
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The nucleoid is a central subcompartment in the cytoplasmwhere DNA aggregates
The nucleoid represents a subcompartment containing thechromosome
Nucleoid
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Most cells have only one copy of each gene(are haploid), so cannot undergo mitosis likeeukaryotes
The complete set of genes is called thegenome
The DNA contains the genes (hereditaryinformation)
The chromosome is usually a closed loop ofDNA and protein
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R plasmids carry genes for resistance to
antibiotics
Plasmids can be transferred between cells and
can be used as vectors in genetic engineering
Each plasmid is a closed loop, containing 5-10genes
Plasmids are molecules of DNA smaller thanthe chromosome
Plasmids Are Found in Many Prokaryotic Cells
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Magnetosomes contain crystals of magnetite or greigite, allowingcells to respond to magnetic fields
Some aquatic bacteria use gas vesicles to float on the waterssurface
Inclusion bodies store nutrients or building blocks for cellularstructures
There are hundreds of thousands of ribosomes, used for proteinsynthesis
Other Subcompartments Exist in the Prokaryotic Cytoplasm
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The Prokaryotic Cell
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End of Chapter 4
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