Please enable JavaScript.
Coggle requires JavaScript to display documents.
CH. 19 Viruses & Ch. 27 Bacteria and Archaea - Coggle Diagram
CH. 19 Viruses & Ch. 27 Bacteria and Archaea
Rapid reproduction, mutation,
and genetic recombination promote genetic
diversity in prokaryotes
Genetic Recombination
Genetic recombination, the combining of DNA from
two sources, contributes to prokaryote diversity
DNA from different individuals can be combined by
transformation, transduction, or conjugation
Transformation and Transduction
In
transformation
, prokaryotic cells incorporate
foreign DNA taken up from their surroundings
In
transduction
, phages (from “bacteriophages,”
viruses that infect bacteria) carry prokaryotic genes
from one host cell to another
For example, a nonpathogenic cell could take up a
piece of DNA carrying an allele for pathogenicity and
replace its own allele with the foreign allele
Conjugation and Plasmids
Conjugation
is the process through which DNA is
transferred between two prokaryotic cells
A piece of DNA called the
F factor
(F for fertility) is
required for the production of pili
The F Factor as a Plasmid
Cells containing the
F plasmid
(F+ cells) function
as DNA donors
Cells lacking the
F factor
(F– cells) are recipients
An F+ cell can convert an F– cell to an F+ cell if it
transfers an entire F plasmid to the F– cell
If only part of the F plasmid’s DNA is transferred,
the recipient cell will be recombinant
The F Factor in the Chromosome
Cells that have the F factor in their chromosome :
(
Hfr
cells, named for high frequency of
recombination) function as donors during
conjugation
Homologous segments of the chromosomal DNA
from the Hfr cell recombines with that of the F– cell
R Plasmids and Antibiotic Resistance
Antibiotics kill most bacteria, but not those with
R
plasmids
, plasmids that carry resistance genes
Some R plasmids carry genes for resistance to
multiple antibiotics
A virus consists of a nucleic
acid surrounded by a protein coat
A
virus
is an infectious particle consisting of genes
packaged in a protein coat
Structure of Viruses
Viruses are not cells
Viral Genomes
double- or single-stranded DNA
double- or single-stranded RNA
Capsids and Envelopes
A
capsid
is the protein shell that encloses the viral
genome
Capsids are built from protein subunits called
capsomeres
Viral envelopes
(derived from membranes of host
cells) surround the capsids of influenza viruses and
many other viruses found in animals
Bacteriophages
, also called
phages
, are viruses
that infect bacteria
Viruses
Smaller than bacteria
non-living
Viruses replicate only in host
cells
Each virus has a
host range
, a limited number of
host species that it can infect
For example, measles virus only infects humans
Replicative Cycles of Phages
Phages have two alternative reproductive
mechanisms: the lytic cycle and the lysogenic cycle
The Lytic Cycle
The
lytic cycle
is a phage replicative cycle that
culminates in the death of the host cell
Produces new phages and lyses
(breaks open) the host’s cell wall, releasing the
progeny viruses
A phage that reproduces only by the lytic cycle is
called a
virulent phage
The Lysogenic Cycle
The l
ysogenic cycle
replicates the phage genome
without destroying the host
The viral DNA molecule is incorporated into the
host cell’s chromosome
Phages that use both the lytic and lysogenic cycles
are called
temperate phages
The integrated viral DNA is known as a
prophage
Every time the host divides, it copies the phage
DNA and passes the copies to daughter cells
Bacterial Defenses Against Phages
Foreign DNA can be identified as such and cut up
by cellular enzymes called
restriction enzymes
Both bacteria and archaea can protect themselves
from viral infection with the CRISPR-Cas system
t is based on sequences called clustered regularly
interspaced short palindromic repeats
(CRISPRs)
Replicative Cycles of Animal Viruses
Viral Genetic Material
The broadest variety of RNA genomes is found in
viruses that infect animals
Retroviruses
use
reverse transcriptase
to copy
their RNA genome into DNA
HIV (human immunodeficiency virus)
is the
retrovirus that causes
AIDS (acquired
immunodeficiency syndrome)
The viral DNA that is integrated into the host
genome is called a
provirus
Unlike a prophage, a provirus remains a permanent
resident of the host cell
Structural and functional
adaptations contribute to prokaryotic success
Cell-Surface Structures
Most bacterial cell walls instead contain
peptidoglycan
, a network of sugar polymers cross-
linked by polypeptides
Scientists use the
Gram stain
to classify bacteria
by cell wall composition
Gram-positive
bacteria have simpler walls with a
large amount of peptidoglycan
The walls of
gram-negative
bacteria have less
peptidoglycan and are more complex with an outer
membrane that contains lipopolysaccharides
Gram-negative bacteria tend to be more resistant to
antibiotics than gram-positive bacteria
Many antibiotics target peptidoglycan and damage
gram-positive bacterial cell walls
Many prokaryotes have a sticky layer of
polysaccharide or protein surrounding the cell wall
is called a
capsule
if it is dense and well-defined
a
slime laye
r if it is not well organized (loosely constructed)
Endospores
can withstand extreme conditions and
remain viable for centuries
Some prokaryotes have hairlike appendages called
fimbriae
that allow them to stick to their substrate
or other individuals in a colony
Pili
(or sex pili) are longer than fimbriae and
function to pull cells together enabling the
exchange of DNA
Motility
About half of all prokaryotes exhibit
taxis
, the ability
to move toward or away from a stimulus
For example,
chemotaxis
is the movement toward or
away from a chemical stimulus
Flagella are the most common structures used by
prokaryotes for movement
Internal Organization and DNA
Prokaryotes lack a nucleus; the chromosome is in
the
nucleoid
, a region with no membrane
Prokaryotes may also have smaller rings of
independently replicating DNA called
plasmids
Reproduction
Prokaryotes reproduce quickly by
binary fission
They have short generation times
Viruses and prions are
formidable pathogens in animals and plants
Viral Diseases in Animals
A
vaccine i
s a harmless derivative of a pathogen
that stimulates the immune system to mount
defenses against the harmful pathogen
Viral infections cannot be treated by antibiotics
Antiviral drugs can help to treat, not cure, viral
infections by inhibiting synthesis of viral DNA and
by interfering with viral assembly
Diseases caused by viral infections affect humans,
agricultural crops, and livestock worldwide
Smaller, less complex entities called prions also
cause disease and animals
Emerging Viral Diseases
Emerging viruses are those that suddenly become
apparent
HIV, the AIDS virus, is a classic example
In 2014, a widespread outbreak
(epidemic)
of
Ebola virus occurred
A global epidemic like this is called a
pandemic
EX: A deadly strain of H1N1, originally called the swine
flu
Prions
Prions
are infectious proteins that appear to cause
degenerative brain diseases in animals
Scrapie in sheep, mad cow disease, and
Creutzfeldt-Jakob disease in humans are all
caused by prions
Prions are incorrectly folded proteins, can be
transmitted in food, act slowly, and are virtually
indestructible
Diverse nutritional and
metabolic adaptations have evolved in
prokaryotes
Prokaryotes can be categorized by how they obtain
energy and carbon:
Phototrophs
obtain energy from light
Chemotrophs
obtain energy from chemicals
Autotrophs
require CO2 or related compounds as a
carbon source
Heterotrophs
require an organic nutrient to make
other organic compounds
The Role of Oxygen in Metabolism
Obligate aerobes
require O2 for cellular respiration
Obligate anaerobes
are poisoned by O2 and live by
fermentation or use substances other than O2 for
anaerobic respiration
Facultative anaerobes
can use O2 if it is present or
carry out fermentation or anaerobic respiration if no
Nitrogen Metabolism
Prokaryotes metabolize nitrogen in many forms
For example, some prokaryotes convert atmospheric
nitrogen (N2) to ammonia (NH3) in a process called
nitrogen fixation
Heterocysts- site of nitrogen fixation
Metabolic Cooperation
Cells of one or more prokaryote species cooperate
to form surface-coating colonies called
biofilms
Biofilms are common in nature, but can cause
many problems for humans including
Corrosion of industrial structures and products
Contamination of medical devices
Tooth decay
Chronic, antibiotic-resistant infections