Transcript Prokaryote Lecture

The earliest cells???
• Membranes may have separated various
aggregates of self-replicating molecules
– Which could be acted on by natural selection
Membrane
LM 650
RNA
Figure 16.6B, C
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Polypeptide
PROKARYOTES
16.7 Prokaryotes have inhabited Earth for billions
of years
• Prokaryotes are the oldest life-forms
Figure 16.7
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Colorized SEM 650 
– And remain the most numerous and
widespread organisms
16.8 Bacteria and archaea are the two main
branches of prokaryotic evolution
• Domains Bacteria and Archaea
– Are distinguished on the basis of
nucleotide sequences and other molecular
and cellular features
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Domain Archaea
16.12 Archaea thrive in extreme environments—
and in other habitats
• Archaea are common in
– Salt lakes, acidic hot springs, deep-sea
hydrothermal vents
Figure 16.12A, B
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• Differences between Bacteria and Archaea
Table 16.8
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16.9 Prokaryotes come in a variety of shapes
• Prokaryotes may be shaped as
– Spheres (cocci)
– Rods (bacilli)
Figure 16.9A–C
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Colorized SEM 3,000 
Colorized SEM 9,000 
Colorized SEM 12,000 
– Curves or spirals
External Structures
• The cell wall
– Is one of the most important features of
nearly all prokaryotes
Capsule
Figure 16.10A
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Colorized TEM 70,000 
– Is covered by a sticky capsule
The Cell Wall
•Made of peptidoglycan- a carbohydrate matrix
(polymers of sugars) cross-linked by short
polypeptide subunits
•Depending on the thickness of the cell wall,
bacteria are classified as gram positive or gram
negative
•Danish microbiologist Hans Christian Gram
developed the staining procedure
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Gram positive bacteria
•Have a thick peptidoglycan layer which accepts
the purple gram stain
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Gram negative bacteria
•Have a multilayered and complex cell wall
•The outside layer is a membrane made of lipopolysaccharide
(sugars and lipids) and a thin peptidoglycan layer inside
which does not accept the purple gram stain
•These layers often make them resistant to antibiotics
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• Some prokaryotes
– Stick to their substrate with pili
– It is also used to transfer DNA from one bacterium to another
during conjugation (sex)
Figure 16.10B
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Colorized TEM 16,000 
Pili
Capsule
•Jelly like coating surrounding the cell wall
•Prevents the cell from drying out
•Helps the cells stick together or on host organisms
•Helps them slide on surfaces
•Prevents the host from killing them
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Motility
• Many bacteria and archaea
– Are equipped with flagella, which enable them to move
Flagellum
Colorized TEM 14,000
– They swim by rotating their flagella
Plasma
membrane
Cell wall
Figure 16.10C
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Rotary movement of
each flagellum
• Some prokaryotes can withstand harsh
conditions
– By forming endospores
TEM 34,000 
Endospore
Figure 16.10D
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Internal Organization
• Some prokaryotic cells
– Have specialized membranes that perform
metabolic functions
Figure 16.10E
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Thylakoid
membrane
TEM 6,000
TEM 45,000
Respiratory
membrane