Ch. 27 Bacteria and

ArchaeaObjective:

Understand the general structure and motility of bacteria and how genetic recombination increases

diversity.

27.1 Structural and Functional Adaptations Contribute to Prokaryotic

Success• Very adaptable (extreme salt, pH, and temp).• Most are unicellular (0.5-5 um) but still perform

all of life’s functions.

(a) Spherical (b) Rod-shaped (c) Spiral

1 m

1 m

3 m

Cell Surface Structures

• All bacteria have a cell wall.• Archaeal bacteria do NOT have a layer of peptidoglycan

in their cell walls.• Eubacteria have differing amount of peptidoglycan

o Gram positive: stains violet due to thick layer peptidoglycan.o Gram negative: stains red due to extra membrane past

peptidoglycan.(a) Gram-positive bacteria: peptidoglycan traps crystal violet.

Gram-positivebacteria

Peptido-glycanlayer

Cellwall

Plasmamembrane

10 m

Gram-negativebacteria

Outermembrane

Peptido-glycanlayer

Plasma membrane

Cellwall

Carbohydrate portionof lipopolysaccharide

(b) Gram-negative bacteria: crystal violet is easily rinsed away, revealing red dye.

Motility• About half of known bacteria can move (taxis)

toward/away from a stimuluso Most commonly via flagella either surrounding the body or found at 1

end. Works like a helicopter with a motor, hook, and filament.

Flagellum

HookMotor

Filament

RodPeptidoglycanlayer

Plasmamembrane

Cell wall

20 nm

Internal Organization and DNA

• No membrane bound organelles but plasma membrane folds on itself to make metabolic membranes.

(a) Aerobic prokaryote (b) Photosynthetic prokaryote

Respiratorymembrane

Thylakoidmembranes

0.2 m 1 m

Internal Organization and DNA

• Smaller, circular DNA found in nucleoid (not nucleus) with very small plasmids (self replicating DNA)

Chromosome Plasmids

1 m

Reproduction and Adaptation

• Reproduce every couple of hours (under optimal conditions) by binary fission.o Division stops due to space limits, metabolic toxins, eaten, etc.o Short generation time leads to quick evolution.

Reproduction and Adaptation

• Endospores develop in harsh conditions.o Duplicated DNA in a tough, multilayered structure.o Water is removed and metabolism stops.

Coat

Endospore

0.3 m

27.2 Rapid Reproduction, Mutation, and Genetic Recombination Promote Genetic Diversity in

Prokaryotes

• 3 mechanisms for prokaryotic genome combinationso Transformationo Transductiono Conjugation

Transformation• Changes genotype

and phenotype by uptake of foreign DNAo Ex: harmless strains of the

bacteria that can cause pneumonia become pathogenic if they come in contact with a pathogenic cell.

Transduction• A “mutant” phage

with bacterial DNA infects a bacteria cell.

Recombinant cell

Recipientcell

Recombination

A

A

A B

BA

Donor cell

A B

BA

Phage

Conjugation• A donor bacteria makes a copy of its DNA,

attaches to another bacteria via a (sex) pilus, the DNA travels to recipient forming a recombined cell.

Sex pilus

1 m

F plasmid Bacterial chromosome

F cell(donor)

F cell(recipient)

Matingbridge

Bacterialchromosome

(a) Conjugation and transfer of an F plasmid

Hfr cell(donor)

F cell(recipient)

(b) Conjugation and transfer of part of an Hfr bacterial chromosome

F factor

A

A

A

A

A

A A

F cell

F cell

AA

RecombinantF bacterium

A