Prokaryotes

1
Prokaryotes

• Theyre almost everywhere

2
(No Transcript)
3
Prokaryotes were the first organism and persist
today as the most numerous and pervasive of all
living things.
4
Archaea and Bacteria are the two main branches of
prokaryotic evolution. Prokaryotes account for
two of three domains (super kingdoms) of
life. Molecular systematics suggests that
archaebacteria (domain Archaea) may be more
closely related to eukaryotes (domain Eukarya)
than to eubacteria (domain Bacteria).
5
Diverse Adaptations of Form and Function
Prokaryotes are generally single celled
organisms, although some occur as aggregates,
colonies, or simple multi-cellular forms.
6
Diverse Adaptations of Form and Function
Prokaryotes are generally single celled
organisms, although some occur as aggregates,
colonies, or simple multi-cellular forms. The
three most common prokaryotic shapes are
spherical (cocci) , rod shaped (bacilli), and
helical forms.
7
Diverse Adaptations of Form and Function
Prokaryotes are generally single celled
organisms, although some occur as aggregates,
colonies, or simple multi-cellular forms. The
three most common prokaryotic shapes are
spherical (cocci) , rod shaped (bacilli), and
helical forms. Nearly all prokaryotes have
external cell walls, which protect and shape the
cell and prevent osmotic bursting. Cell walls of
eubacteria typically contain the polymer
peptidoglycan. Gram-positive and gram-negative
bacteria differ in the structure of their walls
and other surface layers.
8
(No Transcript)
9
ADAPTATIONS

• Many species secrete sticky substances that form
  capsules. Some have surface appendages called
  pili outside the cell wall. Both structures help
  the cells adhere to one another, and some pili
  are specialized for conjugation.
• Motile bacteria propel themselves by flagella,
  use flagella-like filaments positioned inside the
  cell wall (spirochetes) or glide on slime
  secretions.
• Prokaryotic cells are not compartmentalized by
  endomembranes. However, invaginations of the
  plasma membrane may provide internal membrane
  surface for specialized functions.

10
Domain Archaea(Archaebacteria)
Domain Bacteria(Eubacteria)
Domain Eukarya (Eukaryotes)
Universal ancestor
11
A Comparison of the Three Domains of Life
Domain
Charactaristic Bacteria Archaea Eukarya
Nuclear Envelope Absent Absent Present
Membrabce-enclosed organelles Absent Absent Present
Peptidoglycan in cell wall Present Absent Absent
Membrane lipids Unbranched hydrocarbons Some branced hybrocarbons Unbranched hybrocarbons
12
Characteristic Bacteria Archaea Eukarya
RNA polymerase One kind Several Kinds Several kinds
Initiator amino acid for start of protein synthesis Formyl-methionine Methionine Methionine
Introns (noncoding parts of genes) Absent Present in some genes Present
Antibiotic sensitivity Growth inhibites by streptomycin and chloramphenicol Not inhibited by these antibiotics Not inhibited by these antibiotics
13
DNA

• The prokaryotic genome consists of a single
  circular DNA molecule in a nucleoid region
  unbounded by a membrane.
• Many species also possess smaller separate rings
  of DNA called plasmids, which code for special
  metabolic pathways and resistance to antibiotics.

14
REPRODUCTION

• Bacteria reproduce asexually.
• The type of cell division by which these
  prokaryotes reproduce is called binary fission.
• During binary fission, each dividing daughter
  cell receives a copy of the single parental
  chromosome.

15
VARIATION

• Genetic variation occurs in prokaryotes through
  mutation and gene transfer.
• All major types of nutrition and metabolism
  evolved among prokaryotes.
• The evolution of prokaryotic metabolism was both
  cause and effect of changing environments on
  Earth.

16
IMPACT TODAY

• Prokaryotes continue to have an enormous
  ecological impact.
• Prokaryotes, along with fungi, are decomposers
  that recycle chemical elements in ecosystems.
• Some prokaryotes live with other species in
  symbiotic relationships.

17
PROKARYOTES TODAY

• Some parasitic prokaryotes are pathogenic,
  causing disease in the host.
• Bacteria have been put to work in laboratories,
  sewage treatment plants, and the food and drug
  industry.

18
EUKARYOTES

• Eukaryotes originated by symbiosis among
  prokaryotes.
• The first eukaryotes to evolve from prokaryotic
  ancestors were probably unicellular.
• The primal eukaryotes were ancestral to plants,
  fungi, and animals, the eukaryotic organisms most
  familiar to us.

19
PROCESS I

• INVAGINATION OF THE PLASMA MEMBRANE.
• The nuclear envelope, endoplasmic reticulum,
  Golgi apparatus, and related structures, may have
  evolved from specialized invaginations
  (infoldings) of the prokaryotic plasma membrane.

20
PROCESS II

• ENDOSYMBIOSIS-Dr. Lynn Margulis of the University
  of Massachusetts
• Eukaryotic cell arose as a result of prokaryotes
  taking up residence inside other prokaryotes.
• The term endosymbiont is used for a cell that
  lives within another cell, termed the host cell.