Transcript Ch 24 - Bacteria

Ch 24 - Bacteria
Evolution and Classification
Biology of Bacteria
Bacteria and Humans
Evolution – Page 467

Classification
◦ Few morphological differences for use of classification
◦ Traditionally grouped based on structure, physiology,
molecular composition, and reaction to specific types
of stains

Kingdom Archaebacteria – more ancient
◦ Peptidoglycan – protein/CHO cmpd found in cell
walls of Eubacteria but lacking in Archae
◦ Methanogens – harvest E by converting H2 and CO2
into methane gas (bottom of swamp/sewage)
anaerobic
◦ Extreme Halophiles – salt-loving; use salt to generate
ATP (Great Salt Lake & Dead Sea)
◦ Thermoacidophiles – extremely acidic environs; high
temps (hot springs & volcanic vents/hydrothermal
vents)
Evolution

Kingdom Eubacteria –
“Bacteria”
◦ Account for most bacteria
◦ baccili, cocci (strepto- &
staphylo-), spirilla
◦ Gram Stain
 Gram-positive = retain stain
(appear purple)
 Gram-negative = take up 2ndary
stain (appear pink)
Gram Staining
This is what you are looking for…
Evolution (cont.)
◦ Phylum Cyanobacteria – “blue-green algae” (increase in
nutrients in water = increase in bacteria = eutrophication/population bloom = decrease in
amount of avail. O for fish = dead fish = sad)
◦ Phylum Spirochetes – Gram-negative; some aerobic,
some anaerobic; move in corkscrew-like rotation
◦ Phylum Gram-Positive Bacteria – not all grampositive; some gram-negative share similar molecular
similarities (ex. Actinomycetes…grow in soil and produce many antibiotics)
◦ Phylum Proteobacteria - largest, most diverse
 Enteric Bacteria – gram neg., heterotrophic; live in
intestinal tracts; aerobic & anaerobic (E. coli & Salmonella)
 Chemoautotrophs – gram neg., extract E from minerals
 Nitrogen-fixing – incl. gram neg., (Rhizobium = live symbiotically with
plants) Converts N gas to a usable form that plants can use
Evolution (cont)
Structure

Cell Wall – both (Archae and Eu) have (few don’t) – Eu
have peptidoglycan in their cell walls…gram neg. bacteria
has an outer membrane of lipids and sugars as well making
it impenetrable by some antibiotics

Cell Membrane – lipid bilayer and enzymes that catalyze rxns of
cell respir; no mitochondria, so cell mem creates proton gradients to carry
out cell resp.

Cytoplasm – viscous; ribosomes and DNA (DNA arranged in single,
closed loop; some have plasmids, too)

Capsules and Pili – made of polysaccharides allowing it to cling to
cells to keep out harsh chemicals and retain moisture; protection from WBCs;
glycocalyx
Structure (cont.)

Endospores – dormant structure produced by some Gram-Pos.
bacterial species that are exposed to harsh environmental conditions
◦ Thick outer covering that surrounds cell’s DNA
◦ Original cell may be destroyed in harsh conditions (high temps., harsh
chemicals, radiation, drying, and other environ. Extremes), endospore will
survive
◦ Not reproductive
◦ When conditions become favorable, endospore will open, allowing bacterium
to begin multiplying again

Movement Structures – many use flagella, but not all
◦ Can have only one or many flagella
◦ Those that do not have flagella can move using slime, some are shaped (spiral)
that allow them to twist
Nutrition and Growth
Saprophytes – Heterotrophic; feed on dead and decaying material
 Photoautotrophs – Use sunlight as E source (cyannobacteria)
 Obligate Anaerobes – cannot survive in O (Clostridium tetani)
 Facultative Anaerobes – Can live with or without O
 Obligate Aerobes – Need O to survive (Mycobaterium tuberculosis)
 Thermophilic – Grow best between 104ºF-230ºF

Genetic
Recombination

Transformation – When bacterial cell takes in DNA from its
external environment; new DNA is then substituted for a similar DNA fragment in
the chromosome of the bacterial cell

Conjugation – 2 living bacteria bind together; one bacterium
transfers genetic information to the other
◦ Genetic donor must have a specialized plasmid and pilus (binds to recipient, forming
conjugation bridge)
◦ Plasmid replicated in donor bacterium, then copy crosses bridge and cells separate

Transduction – Virus obtains a fragment of DNA from host bact.
◦ After newly formed viruses have been released, they carry the bacterial gene to
a new bacterium, where it can be expressed by the recipient bacterium
Just for a giggle…
Bacteria
and Humans

Bacteria and disease – bacteria that
cause disease = pathogens
◦ Exotoxins and Endotoxins – Exo = toxins made of protein;
produced by Gram+; secreted into surrounding enviro (tetanus) by living
bacteria…Endo = toxins made of lipids and CHO; outer mem of Gram-; released by
Gram- when bacteria die
 Endotoxins
= cause fever, body aches, weakness, and damage vessels of
circulatory system
◦ Antibiotics – drugs that combat bacteria by interfering with various cellular
functions; many derived from chemicals that bacteria and fungi produce (see Table 245)
◦ Antibiotic Resistance – bacteria mutate and become unaffected by
antibiotic designed to eradicate it; resistant population grows from mutant bacteria
(reproduction and genetic recom.)…overuse encourages resistance and makes it
difficult to treat certain bacteria
Useful
Bacteria

Sewage Treatment
◦ Break down remains of organic matter in dead plant and animal waste (recycling
C and N)

Producing/Processing Food
◦ Ferment lactose; digest protein in milk;

Industrial Chemical Production
◦ Produce organic chemicals and fuels; mining for minerals; petroleum recovery;
insecticides; cleaning up environmental disasters (chemical and oil spills)
Viruses
Structure
Viral Replication
Viruses and Human Disease
Structure

Advent of Virology
◦ Wendell Stanley = work suggested that viruses
may be chemicals rather than tiny cells
◦ Virology = study of viruses
◦ Provides clues to biochemistry of living
organisms (mutations, combination of genetic
material from different sources, & other
essential processes of genetics
◦ Used by pharmaceutical companies to develop
new antiviral medications
Characteristics
of Viruses

Viral structure
◦ Capsid – Protein coat surrounding nucleic
acid
◦ Envelope – Made mostly of lipids; taken
from host cell mem. during replication (allows new
viruses to infect host cells during 1st stage of viral
replication
◦ Glycoprotein – Protein containing sugar
chains used to attach to host

Viral shape
Grouping Viruses

Types
◦ DNA – May act 1.)
virus may directly produce RNA that then makes more
viral proteins OR 2.) it may join with the host cell’s DNA to direct the synthesis of
new viruses
◦ RNA – upon entering host, viral RNA is released into host cell’s cytoplasm
where it uses hosts ribosomes to produce viral proteins
◦ Retroviruses – RNA virus; contains enzyme called reverse transcriptase in
addition to RNA
◦ Reverse transcriptase – uses RNA as a template to make DNA
Viroids – smallest known particles that are able to replicate
 Prions – abnormal forms of proteins that clump together inside a cell; clumping

eventually kills cell; found on mammalian cell surfaces and in brain of hosts; been linked
to diseases like scrapie, mad cow disease, and possibly Creutzfeld-Jakob disease
Viral Replication

Bacteriophage – viruses that infect bacteria
◦ Replication cycles are similar to those of viruses of colds, measles, and acquired
immune deficiency syndrome
◦ T phages (most commonly studied) infect E. coli
Lytic Cycle

Virulent – virus invades host, produces new viruses, destroys
host, and releases newly formed viruses
◦ Attaches tail fibers to receptor site
Lysogenic cycle

Temperate – virus that replicates through this cycle and does not kill the host
immediately

Lysogeny in bacteriophages
◦ Attaches to host
◦ Injects DNA
◦ Integrates viral DNA into hosts genome (prophage)
◦ Multiplication of host cell with viral DNA

Lysogeny in HIV
◦ RNA virus
◦ Infects susceptible WBC
◦ Attaches to receptor site, fuses with mem
◦ Viral RNA and reverse transcriptase are
released into cytoplasm
◦ Rev.tran. Transcribes viral RNA into DNA
◦ Viral DNA inserted into hosts genome
◦ Called “Provirus”
Viral Evolution
Believed to have evolved from early cells due to
dependence on other cells to replicate
 Flu viruses (influenza) invade, most destroyed by
immune systems/few escape destruction possibly
due to mutation, invade cells, produce thousands
 These mutations make it difficult for immune
system to recognize it immediately (eventually
will) and many new viruses form
 Difficult to develop vaccines that prevent these
viral infections over long periods of time

◦ Flu vaccine targets a different strain of influenza each year
Viruses and Human Disease
Among most widespread illnesses in
humans
 Mild fevers
to cancers; include
several other severe and fatal diseases

Infectious Diseases
Many use humans as hosts – common cold,
chicken pox, measles, mumps, polio, rabies, hepatitis
 Can affect various organs (brain, liver, heart, lungs,
and skin)
 Rabies…virus carried in saliva of infected animal
 Chicken pox…highly contagious…often recovery is usually followed by
lifelong resistance…if not all is destroyed…persist as a provirus and
cause shingles

Prevention and Treatment

Antiviral drugs – drugs that interfere with the viral nucleic acid synthesis
◦ Types of virus vaccines
 Inactivated – Do not replicate in a host system
 Attenuated – viruses that have been genetically altered so that they are
incapable of causing disease under normal circumstances
 Preferred over those made from inactivated viruses because protection is
greater and lasts longer
 Booster shots – additional doses of some vaccines; extend a person’s
protection against some viruses
 1960’s = measles, mumps, and rubella
 1980’s = hepatitis B
 1990’s = chickenpox, hepatitis A
 AIDS = scientists are still working on this vaccine, but genetic diversity and
mutability create problems

New viruses emerge in
different parts of world
◦ Exist in isolated habitats (infect
humans when habitats are
developed)
◦ Tearing down rainforests may
contribute (Democratic Republic of
Congo) – Ebola virus
 Humans exposed to virus-infected
animals
 Ex. Hantavirus, Manchupo virus, HIV,
Ebola(4 known strains – one affects
monkeys, other 3 are deadly to humans),
Lassa fever virus
 Sometimes difficult to locate host and
figure out where it originated
Emerging
Viruses
Viruses and Cancer
Cancer = uncontrolled reproduction of cells; invade surrounding tissue
 Scientists believe that cancers may be traced to genes
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
within normal cells…genes become mutated (by outside agent =
cigarette smoke, asbestos, sunlight, chemicals, or
radiation)…stimulated to multiply uncontrollably
Lysogenic viruses may trigger cancer genes
See table 25-3