Prokaryotes
AP Biology
Spring 2011
 Domains
the two domains of prokaryotes
 Describe the unique characteristics of
prokaryotes and their metabolic diversity
 Discuss how prokaryotes reproduce
 Give examples of positive and negative
impacts of bacteria on humans
Viruses
 Read
chapter 21.1-21.2
 Good refresher on viruses
 Remember:


Structure
Viral replication

http://www1.teachertube.com/viewVideo.php?title=V
iral_infection_and_replication&video_id=50887
Viroids and Prions
 Since
the 1970’s about 30 viroids have been
identified
 A viroid is a small circle of RNA that can
affect organisms
 Most affect plants; only one viroid known to
affect humans
 Prions are misfoldings of proteins


Accumulate in nervous system cells
Cause cell death and a spongiform pathology in
the brain cell
Prokaryotes- Enduring, Abundant, and Diverse
 The
earliest cells were prokaryotes, cells
with no nucleus
 Bacteria:

Classified based on shape, cell wall properties,
metabolism, and other properties
Automated gene
sequencing has
elucidated prokaryote
diversity
 Shortly after life
began there was a
branching between
bacteria and Archae



Which eventually led to
Eukaryote lineage
Despite estimates of
millions of species of
bacteria, only about
5,000 named
 Bacteria
are very successful and terms of
reproduction
 Metabolic diversity is key to reproductive
success in bacteria
 Metabolic

Photoautotrophs are
photosynthetic


diversity:
Cyanobacteria
Chemoautotrophs use
electrons that they strip
from inorganic compounds
and use that energy to
build organic compounds
from CO2 and water


Photoheterotrophs use light energy and obtain
carbon from organic compounds from their
environment
Chemoautotrophs get both their carbon and their
energy by breaking down organic compounds


This group includes many prokaryotes, some protists,
and all animals and fungi
Usually parasites- get butrients from living host
Prokaryotic Structure and Function
 Modern
prokaryotes include bacteria and
archeans

They are unicellular and do not enclose their DNA
in a nucleus
 All
prokaryotes have ribosomes
 Some have infoldings of their membrane
 Nearly all have a cell wall, some have an
external slime coat that helps them adhere
to surfaces
 Gram
staining: can identify many
bacteria species by their wall
staining properties
 Unknown species exposed to
purple dye, then iodine, then
alcohol wash, and finally a
counterstain
 Gram-positive: stays purple
 Gram-negative: loses colour at
first, then counterstain turns it
pink
 Glycocalyx:
sticky mesh, consists of
polysaccharides, polypeptides, or both


Capsule: when highly organized and attached
firmly
Slime layer: when less organized, and loosely
attached
 Three

Coccus:


Spherical
Bacillus:



basic shapes:
Rod
Cylindrical
Spirillum:

Helical
 Two
kinds of filamentous structures may be
attached to the cell wall


Bacterial flagellum: rotates like a propeller to pl
the cell along
Pili: help bacteria attach to another in
conjugation (exchange of DNA), or help them
attach to surfaces
 Reproductive
rates in prokaryotes are high,
some species can reproduce every 20
minutes
 Some species reproduce using a budding
mechanism
 More commonly, reproduce with fission that
is similar to mitosis
 Some
bacteria can also pass along genes
without reproducing
 During conjugation a plasmid, a small, selfreplicating circle of DNA containing only a
few genes, can be passed to another cell
 Some
F (fertilty) plasmids allow bacteria to
engage in bacterial conjugation in which a
pilus joins two prokaryotic cells to permit
the transfer of plasmid DNA
Prokaryotic Growth and Reroduction
 When
a bacterium divides, each daughter
cell inherits a single chromosome

Circular double-stranded DNA molecule
 Bacteria


reproduce by prokaryotic fission
Results in two genetically identical daughter cells
Only bacteria and archaens reproduce by this
type of cell division
A
plasmid is small, self-replicating circle of
DNA containing only a few genes
 Some F (fertility) plasmids allow bacteria to
engage in bacterial conjugation in which a
pilus joins two prokaryotic cells to permit
transfer of plasmid DNA
Conjugation
The Bacteria
 Thermophiles
exist in extreme environments
 Members of the genus Aquifex include
bacteria that live in volcanic spring, thermal
vents, and hot springs
 Chloroplast-containing
bacteria
 Anabaena: by means of heterocysts, can fix
nitrogen
 Make
up largest, most diverse bacterial group
(gram negative)
 Theiomargarita namibiensis:

Chemeoautotroph that lives in marine
environments and gets its energy from striping
electrons from sulfur
 Rhizobium:
legumes
fixes nitrogen on roots of
 E.

Coli & H. Pylori:
Live in human digestive system
 E.
Coli 
 Some
free living, chemoautotrophic
proteobacteria exhibit complex behavior

Magnetoacteria: attracted by magnetic fields

Myxobacteria: move as a group and feed on soil
bacteria
 Gram

Not a monophyletic group


Positive:
If all organisms in that group are known to have
developed from a common ancestral form, and all
descendants of that form are included in the group
Most are chemioheterotrophs with thick cell
walls that retain gram stain
 Lactobacillus:
used in dairy product
conversions such as yogurt
 L.acidophilus: lowers the pH of skin and
vaginal linings
 Some form resistant endospores that can
survive harsh environmental conditions

Ex. Clostridium tetani (tetnus)
Tetnus
 Spirochetes:


resemble a spring
Resposible for causing Lyme disease
Free living parasites or symbionts
 Clamydias:
intracellular parasites that affect
animal cells

Cannot make DNA, pilfer it from cells
Archaeans
 Archaeans:
differ in their
ribosomal DNA and cell
walls



Resemble eukaryotic cells by
making histones and sharing
the same start codon for
transcription
Some may resemble first
cells on Earth
Recently this group has been
subdivided into 3 major
groups




Methane makers
Inhabit swamps, mud, sewage, and animal guts
Make ATP anaerobically by converting carbon dioxide and
hydrogen to methane
Free oxygen kills them
 Salt
lovers
 Can tolerate high salt environments such as
brackish ponds, salt lakes, volcanic vents on
seafloor, and the like
 Most are heterotrophic aerobes, some can
switch to a special photosynthesis, using
bacteriorhodopsin to produce ATP

Light activating pigment embedded in plasma
membrane, when it absorbs sunlight energy,
changes shape and pumps H+ out from cell. H+
flows back into it, through ATP synthase and
drives ATP formation
 Heat
lovers
 Live in hot springs and other very hot places
such as thermal vents of the sea floor where
temps exceed 250 degrees C
 Use sulfur as source of electrons for ATP
formation