BIO 205 Chapter 4 Powerpoint

BIO 205
Chapter 4
The Domain Bacteria Contains Some of the Best Studied Prokaryotes
The majority of the 18 phyla of Bacteria play a positive role in

nature
•Proteobacteria contain the largest and most diverse group of

species, including E. coli and many human pathogens
•Firmucutes consist of many gram-positive species, such as

Bacillus, Clostridium, Staphylococcus, and Streptococcus
•Actinobacteria include Streptomyces, the genus that produces the

antibiotic streptomycin
•Cyanobacteria carry out photosynthesis using chlorophyll,

responsible for the appearance of oxygen in Earth’s early
atmosphere
•Chlamydiae are extremely small, mostly pathogenic bacteria

The Domain Archaea Contains
Many Extremophiles
Euryarchaeota contain:
• Methanogens (live in
anoxic environments)
• Extreme halophiles (salt

lovers)
• Thermoacidophiles (grow at
high temperature with low
pH
Crenarchaeota tend to grow in

hot acidic environments such
as hot springs and volcanic
vents
The Shapes and Arrangements of Prokaryotic Cells
Three Main Shapes:
Rod
Sphere
Spiral
The Shapes and Arrangements of Prokaryotic Cells
Streptococcus Chain
A spherical bacterial cell is a coccus
Many cocci and some bacilli appear in groups or chains

Spiral shaped bacteria can appear as vibrios (comma-
shaped), spirilla (helical), or spirochete
Prokaryotic Cell
Structure
Pili
Pili Are Protein Fibers Extending from the Surface
of Many Prokaryotes
Pili help:
• Attach cells to surfaces
• Form biofilms and

microcolonies.
Some bacterial
species have
conjugation pili,
used to transfer
genetic material
between cells
Flagella
Prokaryotic Flagella Are Long Appendages
Extending from the Cell Surface
Flagella can be used for cell motility
Prokaryotic
flagella contain a
helical filament,
a hook, and a
basal body
Flagella Continued
Prokaryotic Flagella Are Long Appendages Extending from
the Cell Surface
Bacteria exhibit chemotaxis, moving up the concentration

gradient of a chemical attractant
Some prokaryotes move without flagella by gliding across a

solid surface
The Glycocalyx Is an Outer Layer Glycocalyx
External to the Cell Wall
The glycocalyx is an adhering

layer of polysaccharides (and
sometimes small proteins)
A thick glycocalyx covalently

bound to the cell is a capsule
A thin diffuse layer of

polysaccharides is a slime layer
It protects cells from the

environment, and allows them
to attach to surfaces
Capsule
Capsule in Acinetobacter species by negative staining
Cell Envelope
The cell envelope is
composed of two
parts:
•Cell Wall
•Cell Membrane
The cell wall protects

the cell from injury, and
maintains cell shape
and water balance
Prokaryotic Cell Wall
Cell walls in prokaryotes contain peptidoglycan
Gram-positive bacteria have thick peptidoglycan cell

walls containing teichoic acid
Gram-negative bacteria have a two-dimensional

peptidoglycan layer and no teichoic acid
The gram-negative cell wall has an outer membrane,

separated from the cell membrane by the periplasmic
space
The outer membrane contains proteins called porins

that selectively allow small molecules into the
periplasmic space
Archaeal Cell Wall
The Archaeal Cell Wall Also Provides Mechanical Strength
No archaea have peptidoglycan in the cell wall, but some

have pseudopeptidoglycan
Others have polysaccharides, proteins, or both
The S-layer is the most common archaeal cell wall,

consisting of protein or glycoprotein in a crystal lattice
The Cell MembraneProkaryotic
RepresentsCell Membrane
the Interface between the
Cell Environment and the Cell Cytoplasm
•The cell membrane is a fluid layer of phospholipid and

protein (the fluid mosaic model)
•The phospholipid molecules are arranged in a bilayer
•Hydrophobic fatty acid chains in the phospholipids form a

permeability barrier
Prokaryotic Cell Membrane
The Cell Membrane Represents the Interface between the
Cell Environment and the Cell Cytoplasm
Antimicrobial substances may disrupt or dissolve the

bilayer
Membrane proteins perform or aid in many functions,

such as:
•cell wall synthesis
•energy metabolism
•DNA replication
•sensation of stimuli
•molecule transport
Facilitated Diffusion
Archaeal Cell Membranes
The Archaeal Cell Membrane Differs from Bacterial and

Eukaryotic Membranes
•Hydrophobic lipid tails are attached to glycerol

differently in archaea
•Fatty acids are usually absent
•Adjacent lipid tails are bound together forming a lipid

monolayer, instead of a bilayer
The Cell Cytoplasm and Internal Structures
Nucleoid
The nucleoid represents a subcompartment containing the
chromosome
The nucleoid is a central subcompartment in the cytoplasm

where DNA aggregates
•The chromosome is usually a closed loop of
DNA and protein
•The DNA contains the genes (hereditary

information)
•The complete set of genes is called the

genome
•Most cells have only one copy of each gene

(are haploid), so cannot undergo mitosis like
eukaryotes
Plasmids Are Found in Many Prokaryotic Cells
•Plasmids are molecules of DNA smaller than

the chromosome
•Each plasmid is a closed loop, containing 5-10

genes
•Plasmids can be transferred between cells and

can be used as vectors in genetic engineering
•R plasmids carry genes for resistance to

antibiotics
Other Subcompartments Exist in the Prokaryotic Cytoplasm
•There are hundreds of thousands of ribosomes, used for protein

synthesis
•Inclusion bodies store nutrients or building blocks for cellular

structures
•Some aquatic bacteria use gas vesicles to float on the water’s

surface
•Magnetosomes contain crystals of magnetite or greigite, allowing

cells to respond to magnetic fields
The Prokaryotic Cell
End of Chapter 4

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BIO 205

The majority of the 18 phyla of Bacteria play a positive role in

•Proteobacteria contain the largest and most diverse group of

•Firmucutes consist of many gram-positive species, such as

•Actinobacteria include Streptomyces, the genus that produces the

•Cyanobacteria carry out photosynthesis using chlorophyll,

•Chlamydiae are extremely small, mostly pathogenic bacteria

• Extreme halophiles (salt

Crenarchaeota tend to grow in

Three Main Shapes:

Many cocci and some bacilli appear in groups or chains

• Form biofilms and

Flagella can be used for cell motility

Bacteria exhibit chemotaxis, moving up the concentration

Some prokaryotes move without flagella by gliding across a

The glycocalyx is an adhering

A thick glycocalyx covalently

A thin diffuse layer of

It protects cells from the

The cell wall protects

Gram-positive bacteria have thick peptidoglycan cell

Gram-negative bacteria have a two-dimensional

The gram-negative cell wall has an outer membrane,

The outer membrane contains proteins called porins

The Archaeal Cell Wall Also Provides Mechanical Strength

No archaea have peptidoglycan in the cell wall, but some

Others have polysaccharides, proteins, or both

The S-layer is the most common archaeal cell wall,

•The cell membrane is a fluid layer of phospholipid and

•The phospholipid molecules are arranged in a bilayer

•Hydrophobic fatty acid chains in the phospholipids form a

Antimicrobial substances may disrupt or dissolve the

Membrane proteins perform or aid in many functions,

The Archaeal Cell Membrane Differs from Bacterial and

•Hydrophobic lipid tails are attached to glycerol

•Fatty acids are usually absent

•Adjacent lipid tails are bound together forming a lipid

The nucleoid is a central subcompartment in the cytoplasm

•The DNA contains the genes (hereditary

•The complete set of genes is called the

•Most cells have only one copy of each gene

•Plasmids are molecules of DNA smaller than

•Each plasmid is a closed loop, containing 5-10

•Plasmids can be transferred between cells and

•R plasmids carry genes for resistance to

•There are hundreds of thousands of ribosomes, used for protein

•Inclusion bodies store nutrients or building blocks for cellular

•Some aquatic bacteria use gas vesicles to float on the water’s

•Magnetosomes contain crystals of magnetite or greigite, allowing

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