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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 16Evolution of
Microbial Life
Viruses Reproduce in Living Cells
16-2
16.1 Viruses have a simple structure The size of a virus is comparable to that of a
large protein macromolecule, ranging from 0.2 to 2 μm
All viruses possess the same basic anatomy An outer capsid, which is composed of protein An inner core of nucleic acid (DNA or RNA)
A viral genome has as few as three and as many as 100 genes
The covering of a virus contains the capsid, which may be surrounded by an outer membranous envelope If not, the virus is said to be naked. Naked viruses
can be transmitted by contact with inanimate objects, such as desktops 16-3
16-4
Figure 16.1A Adenovirus, a naked virus, with a polyhedral capsid and a fiber at each corner
16-5
Figure 16.1B Influenza virus, surrounded by an envelope with spikes
16-6
16.2 Some viruses reproduce inside bacteria
All sorts of cells, whether prokaryotic or eukaryotic, are susceptible to a viral infection
Viruses are specific Specificity extends to the type of cell infected by the
virus Example: tobacco mosaic virus infects only tobacco leaves
Bacteriophages, or simply phages, are viruses that parasitize bacteria Two types of bacteriophage life cycles
Lytic cycle and the Lysogenic cycle
16-7
Figure 16.2 The lytic and lysogenic cycles in prokaryotes
16-8
APPLYING THE CONCEPTS—HOW SCIENCE PROGRESSES 16.3 Viruses are responsible for
a number of plant diseases Approximately 2,000 kinds of plant diseases
have been attributed to viruses Plant viruses are responsible for the loss of over
15 billion dollars annually by reducing the yield of important agricultural and horticultural crops
Once a plant is infected the virus spreads slowly throughout the plant
In some instances, plants have been purposefully infected with a virus in order to produce traits considered desirable by gardeners
Example: Some variegation in leaves and flowers can be brought about by viruses
16-9
16-10
Figure 16.3A The tobacco mosaic virus (TMV) is responsible for discoloration in the leaves of tobacco plants
Figure 16.3B A virus is responsible for the variegation and streaking in Rembrandt tulips
16-11
16.4 Viruses reproduce inside animal cells and cause diseases
Replication of an animal virus with a DNA genome involves certain steps Attachment: Glycoprotein spikes projecting through the
envelope allow the virus to bind to host cells Penetration: After the viral particle enters the host cell,
uncoating follows and viral DNA enters the host Biosynthesis: The capsid and other proteins are
synthesized by host cell ribosomes according to viral DNA instructions
Maturation: Viral proteins and DNA replicates are assembled to form new viral particles
Release: In an enveloped virus, budding occurs and the virus develops its envelope
16-12
Figure 16.4 Replication of an animal virus
16-13
16.5 The AIDS virus exemplifies RNA retroviruses
Genome for an HIV virus consists of RNA, instead of DNA
HIV is a retrovirus. It uses reverse transcription from RNA into DNA in order to insert a complementary copy of its genome into the host’s genome
16-14
Figure 16.5 Reproduction of HIV
16-15
APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
16.6 Humans suffer from emerging viral diseases
Emergent diseases - newly recognized as infectious International travel facilitates disease transmission
Viruses are constantly in a state of evolutionary flux A new pathogen can emerge through the acquisition of new
surface antigens Some viruses can easily move from animals to humans
Example: Rabies can be spread by the bite of a rabid animal, such as a skunk, raccoon, bat, cat or dog
Many viruses are transmitted by vectors, usually insects that carry pathogens from an infected individual or reservoir to a healthy individual Mosquitoes serve as a common vector for several viral diseases,
including West Nile virus and yellow fever 16-16
Figure 16.6A Surgical masks provide protection against the transmission of SARS
16-17
Figure 16.6B Exterminating possibly infected chickens may protect against bird flu
16-18
The First Cells Originated on Early Earth
16-19
16.7 Experiments show how small organic molecules
may have first formed Two different hypotheses to explain how organic
molecules could have formed Prebiotic Soup Hypothesis
The early atmosphere contained no oxygen and was a reducing environment
In such an environment, methane, ammonia, hydrogen, and water could be reduced to a variety of amino acids and organic acids
Iron-Sulfur World Hypothesis At hydrothermal vents on the ocean floor, cool water is
heated to a temperature as high as 350°C, and when it spews back out, it contains various mixed iron and nickel sulfides that can change N2 to NH3
16-20
Figure 16.7A Laboratory re-creation of chemical evolution in the atmosphere
16-21
Figure 16.7B Chemical evolution at hydrothermal vents
16-22
16.8 RNA may have been the first macromolecule
Two stages in origin of life Chemical Evolution
Organic monomers arise from inorganic compounds and polymers arise when monomers join together
Biological Evolution A plasma membrane surrounds polymers producing a protocell A true cell has arisen when the cell reproduces in the same manner
as today’s cells
RNA-First Hypothesis The first macromolecules need to have enzymatic functions, not
only to allow the genetic material to replicate, but also to perform any number of metabolic functions
This has led research to conclude it was an “RNA world” some 4 BYA and that RNA chains were the first forms of life
16-23
Figure 16.8 The origin of the first cell(s) can be broken down into these steps
16-24
16.9 Protocells preceded the first true cells
Origin of Plasma Membrane - First and foremost, the protocell would have had an outer membrane Two hypotheses on origin of first plasma membrane
If lipids are made available to microspheres, which are protein, they acquire a lipidprotein outer membrane
Liposomes - Lipids naturally organize themselves into double-layered bubbles, roughly the size of a cell
16-25
Figure 16.9A Microspheres, which are made of protein, could have acquired an outer lipid-protein membrane during the origin of the first cell
16-26
Figure 16.9B Liposomes, which are composed of lipids, have a double-layered outer membrane
16-27
Origin of DNA Information System
A protocell became a cell when it contained a DNA information system DNA to RNA to Proteins
To make DNA, a ribozyme could have acted in the same manner as the enzyme reverse transcriptase RNA is unique in that it could have also synthesized
the proteins that took over most of the enzymatic functions in cells
16-28
Origin of Metabolism to Acquire Energy
The cell would have had to carry on nutrition so that it could grow
Two theories If organic molecules formed in the atmosphere
Nutrition would have been no problem because simple organic molecules could have served as food
Thus the protocell was a heterotroph
If the protocell evolved at hydrothermal vents It may have carried out chemosynthesis Synthesizing organic molecules by oxidizing inorganic
compounds, such as hydrogen sulfide (H2S)
16-29
Both Bacteria and Archaea Are Prokaryotes
16-30
16.10 Prokaryotes have particular structural features
Prokaryotes are unicellular organisms Range in size from 1-10 μm in length and 0.7-1.5 μm in
width Prokaryote means “before a nucleus”
These organisms lack a eukaryotic nucleus, but have a dense area called a nucleoid, consisting of a circular strand of DNA
Three Basic Shapes of Prokaryotes Cocci (sing., coccus) - round or spherical Bacilli (sing., bacillus) - rod-shaped Spirilla (sing., spirillum) - spiral- or helical-shaped
16-31
Figure 16.10A Anatomy of bacteria
16-32
Figure 16.10B The three shapes of prokaryotes
16-33
16.11 Prokaryotes have a common reproductive strategy
Figure 16.11A Binary fission results in two bacteria
16-34
Formation of Endospores in Bacteria
When faced with unfavorable environmental conditions, some bacteria form endospores A portion of the cytoplasm and a copy of the
chromosome dehydrate and are then encased by a heavy, protective spore coat
16-35
Figure 16.11B Endospores within Clostridium tetani, a bacterium
16-36
16.12 How genes are transferred in bacteria
Transformation - a recipient bacterium picks up from its surroundings free pieces of DNA secreted by live prokaryotes or released by dead prokaryotes
Conjugation - the donor bacterium passes DNA to the recipient by way of a sex pilus, which temporarily joins the two bacteria
Transduction - bacteriophages carry portions of bacterial DNA from a donor cell to a recipient When a bacteriophage injects its DNA into the donor cell, the
phage DNA takes over the machinery of the cell and causes it to produce more phage particles
16-37
Figure 16.12A Gene transfer by transformation
16-38
Figure 16.12B Gene transfer by conjugation
16-39
Figure 16.12C Gene transfer by transduction
16-40
16.13 Prokaryotes have various means of nutrition
Obligate Anaerobes - unable to grow in the presence of free oxygen A few serious illnesses—such as botulism, gas
gangrene, and tetanus—are caused by anaerobic bacteria
Facultative anaerobes - able to grow in either presence or absence of oxygen
Most prokaryotes are aerobic and require a constant supply of oxygen
16-41
Autotrophic Prokaryotes
Some prokaryotes produce their own organic nutrients
Photoautotrophs use solar energy to reduce carbon dioxide to organic compounds Two types of photoautotrophic bacteria
Those that evolved first and do not give off oxygen Those that evolved later and do give off oxygen
Chemoautotrophs remove electrons from inorganic compounds, such as hydrogen gas, hydrogen sulfide, and ammonia, and to reduce CO2 to an organic molecule
16-42
Figure 16.13A Some anaerobic photosynthetic bacteria live in the muddy bottom of eutrophic lakes
16-43
Figure 16.13B Some chemosynthetic prokaryotes live at hydrothermal vents
16-44
Chemoheterotrophic Prokaryotes
Many prokaryotes are aerobic saprotrophs They secrete digestive enzymes into the environment to
breakdown large organic molecules to smaller ones to be absorbed
In ecosystems, saprotrophic bacteria are called decomposers They play a critical role in recycling matter and make
inorganic molecules available to photosynthesizers
16-45
16.14 The cyanobacteria are ecologically important organisms Perform photosynthesis like plants and are likely
the first to have generated oxygen Some possess heterocysts for nitrogen fixation Common in aquatic habitats and some harsh
habitats Some are symbiotic with other organisms (e.g.
lichens are cyanobacteria and fungi)
16-46
16.15 Some archaea live in extreme environments
Archaea are found in extreme environments hot springs, thermal vents, and salt basins
They may have diverged from a common ancestor relatively soon after life began
Structure and Function Plasma membranes of archaea contain unusual lipids
that allow them to function at high temperatures Some have unique forms of metabolism
Methanogens have the unique ability to form methane
16-47
Types of Archaea
Figure 16.15A Methanogen habitat and structure 16-48
Figure 16.15B Halophile habitat and structure
16-49
Figure 16.15C Thermoacidophile habitat and structure
16-50
APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES 16.16 Prokaryotes have environmental
and medical importance
Prokaryotes are everywhere Prokaryotes are most cosmopolitan of all life-forms and
are virtually everywhere Found in oceans, our intestines, hot springs, and soil
Prokaryotes were and are environmentally important Ancient photosynthetic cyanobacteria released copious
amounts of oxygen Prokaryotes play an essential role in the carbon
nitrogen, sulfur, and phosphorus environmental cycles16-51
Prokaryotes Are Medically Important
16-52
APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES 16.17 Disease-causing microbes can
be biological weapons Biological warfare is the use of viruses and bacteria
as weapons of war Likely agents to be used by bioterrorists
Anthrax - from the bacterium Bacillus anthracis Smallpox - caused by the variola virus Botulism - caused by the toxin of the anaerobic
bacterium Clostridium botulinum Plague - from the bacterium Yersinia pestis, has been
called the Black Death and bubonic plague Tularemia - caused by the bacterium Francisella
tularensis Hemorrhagic fevers - caused by several types of
viruses, are characterized by high fever and severe bleeding from several organs 16-53
Connecting the Concepts:Chapter 16
Viruses are noncellular, disease-causing agents Medical significance of viruses cannot be underestimated Humans use viruses for gene research and even for gene therapy
Prokaryotes are cellular, but their structure is simpler than eukaryotes They lack a nucleus and membranous organelles
Many prokaryotes live in environments that may resemble habitats available when Earth first formed We find prokaryotes in such hostile habitats as swamps, the Dead
Sea, and hot sulfur springs Cyanobacteria are believed to have introduced oxygen into the
Earth’s ancestral atmosphere Most bacteria are decomposers that recycle nutrients in both
aquatic and terrestrial environments16-54