Transcript Ch.27 Prokaryote Diversity

Chapter 27

Prokaryotes and
the Origins of
Metabolic
Diversity
Overview: They’re (Almost)
Everywhere!




Most prokaryotes are microscopic, but what they
lack in size they make up for in numbers
There are more in a handful of fertile soil than the
number of people who ever lived
Prokaryotes thrive almost everywhere, including
places too acidic, too salty, too cold, or too hot for
most other organisms
They have an astonishing genetic diversity
Concept 27.1: Structural, functional,
and genetic adaptations contribute to
prokaryotic success



Most prokaryotes are unicellular, although
some species form colonies
Prokaryotic cells have a variety of shapes
The three most common of which are spheres
(cocci), rods (bacilli), and spirals (spirilla).
LE 27-2
1 µm
Spherical
(cocci)
2 µm
Rod-shaped
(bacilli)
5 µm
Spiral
(spirilla)
Cell-Surface Structures


An important feature of nearly all prokaryotic
cells is their cell wall, which maintains cell
shape, provides physical protection, and
prevents the cell from bursting in a hypotonic
environment
Using the Gram stain, scientists classify many
bacterial species into groups based on cell wall
composition, Gram-positive and Gramnegative
Lipopolysaccharide
Cell
wall
Pepridoglycan
layer
Cell
wall
Outer
membrane
Pepridoglycan
layer
Plasma membrane
Plasma membrane
Protein
Protein
Grampositive
bacteria
Gramnegative
bacteria
20 µm
Gram-positive
Gram-negative

The cell wall of many prokaryotes is covered
by a capsule, a sticky layer of polysaccharide
or protein
LE 27-4
200 nm
Capsule

Some prokaryotes have fimbriae and pili,
which allow them to stick to their substrate or
other individuals in a colony
LE 27-5
Fimbriae
200 nm
Motility


Most motile bacteria propel themselves by
flagella that are structurally and functionally
different from eukaryotic flagella
In a heterogeneous environment, many
bacteria exhibit taxis, the ability to move
toward or away from certain stimuli
LE 27-6
Flagellum
Filament
50 nm
Cell wall
Hook
Basal apparatus
Plasma
membrane
Internal and Genomic Organization


Prokaryotic cells usually lack complex
compartmentalization
Some prokaryotes do have specialized
membranes that perform metabolic functions
LE 27-7
1 µm
0.2 µm
Respiratory
membrane
Thylakoid
membranes
Aerobic prokaryote
Photosynthetic prokaryote

The typical prokaryotic genome is a ring of
DNA that is not surrounded by a membrane
and that is located in a nucleoid region
LE 27-8
Chromosome
1 µm
Classification




Domain: Bacteria
Domain: Archaea
Kingdom: “Monera?”
Shape
•cocci (sphere)
•bacilli (rod)
•helical (spiral)
Structural characteristics





Cell wall~ peptidoglycan (sugars &
proteins);
√ Gram +: w/peptidoglycan penicillin
action
√ Gram -: little peptidoglycan,
lipopolysaccharides; most pathogens;
impede drug action
Capsule: adherence; protection
Pili: adherence; conjugation
Motility




1- Flagella
2- Helical shape (spirochetes)
3- Slime
4-Taxis (movement away or toward a
stimulus)
Form & Function
Nucleoid region (genophore: non-eukaryotic
chromosome)

Plasmids

Asexual reproduction: binary fission (not mitosis)
“Sexual” reproduction (not meiosis):
1. transformation~ uptake of genes from
surrounding environment

2.
3.

conjugation~ direct gene transfer from one
prokaryote to another
transduction~ gene transfer by
viruses
Endospore: resistant cells for
harsh conditions
(250 million years!)
Nutrition & Metabolism






Photoautotrophs: photosynthetic;
harness light to drive the synthesis of
organics (cyanobacteria)
Chemoautotrophs: oxidation of
inorganics for energy; get carbon
from CO2
Photoheterotrophs: use light to
generate ATP but get carbon in an
organic form
Chemoheterotrophs: consume
organic molecules for both energy
and carbon
saprobes- dead organic matter
decomposers
parasites- absorb nutrients
from living hosts
Nitrogen fixation: conversion of
atmospheric nitrogen (N2) to
ammonium (NH4+)
Oxygen relationships: obligate
aerobes; facultative anaerobes;
obligate anaerobes
Prokaryotic ecology



Decomposers: unlock organics from
corpses and waste products
Symbiosis~
•symbiont/host
•mutualism (+, +)
•parasitism (+, -)
•commensalism (+, 0)
Disease
•opportunistic: normal residents
of host; cause illness when defenses
are weakened
•Koch’s postulates: criteria for
bacterial disease confirmation
•exotoxins: bacterial proteins
that can produce disease w/o the
prokaryote present (botulism)
•endotoxins: components of
gram - membranes (Salmonella)