Transcript the genetics of viruses and bacteria

THE GENETICS OF
VIRUSES
Chapter 19
CHARACTERISTICS OF
VIRUSES
Small (20nm)
Composed of RNA or DNA and
protein
Capsid- protein coat that encloses
the viral genome
Viral envelopes – a membrane
that encloses capsid on some
viruses (derived from host)
Comparing the size of a virus, a bacterium, and a eukaryotic cell
Viral structures
Adenovirus
Bacteriophage – a virus that infects
bacteria
Viruses are obligate parasites – can
only reproduce within a host cell
Host Range – virus can only infect a
limited number of host cells
– Ex. HIV only attacks T-cells
Considered nonliving
Viruses infect all life on the planet
Phages
VIRAL INFECTION
Virus injects its genome (DNA or
RNA) into host cell
Two major reproduction
pathways for phages:
–1. Lytic
–2. Lysogenic
A simplified viral reproductive cycle
The lysogenic and lytic reproductive cycles of phage , a temperate phage
THE LYTIC CYCLE
Ends in death of host cell
Viruses called virulent
Viral DNA inserted into host
Host’s DNA hydrolyzed
Viral DNA makes proteins and more viral
DNA
New viruses released by bursting out of
host cell
THE LYSOGENIC CYCLE
Does not kill host cell
Called temperate viruses
Viral DNA is inserted into host cell
Viral DNA is inserted into host cell’s DNA
(called a prophage)
When host cell replicates it also replicates the
viral DNA section
Prophage genes are mostly inactive
Some can make harmful toxins (ex. diphtheria
and scarlet fever)
Classes of Animal Viruses, Grouped by Type of Nucleic Acid
Classes of Animal Viruses, Grouped by Type of Nucleic Acid
Smallpox
Measles
Polio
Influenza epidemic (Killed 40 million people in 1918-19)
Herpes
RNA VIRUSES
Can be transcribed to make protein
Can make more RNA with special
enzymes (within capsid)
Retrovirus – contain reverse
transcriptase enzyme which transcribes
DNA from RNA. (reverse)
– Ex. HIV
Lack error checking ability during RNA
replication so higher rates of mutation
HIV, a retrovirus
HIV infection
VACCINES
Harmless variants, dead or
derivatives of viruses that allow us
to build an immunity to the real
thing
Antibiotics are powerless against
viruses
EMERGING VIRUSES
Viruses have high mutation rates
Dissemination of virus from small
population to larger (airplanes)
Spread of existing viruses from
other animals
Cancer Causing Viruses
Some viruses can cause cancer
–Ex. Hepatitis B – liver cancer
–Ex. Papilloma – cervix cancer
Hepatitis
INFLUENZA
Three types
– Type A: can cause epidemics and found in
many animals including humans
– Types B and C: only in humans and no
epidemics
Type A contain two proteins on capsid
– H = hemagglutinin (helps virus attach to host)
– N = neuroaminidase (helps release new viruses
from infected cell)
H1N1 (swine flu) and H5N1 (avian flu)
H1N1
– Caused both flu pandemic in 1918 and in 2009
– Probably mutated in pigs and moved to
humans
– 79% people infected were under 30 in 2009
H5N1
– Expanding host range and 50% mutation rate
– Greater threat
– Human to human transmission rare (so far)
PRIONS
Prions are infectious proteins
– Diseases caused by prions: Mad cow,
Creutzfeldt-Jacob, Kuru and maybe
Alzheimer’s
– Misfolded forms of proteins
– Associated with eating infected meat
– Incubate very slowly
– No cure and always deadly
A hypothesis to explain how prions propagate
Bacteria and Archaea
CHAPTER 27
Bacteria on the point of a pin
THREE MAIN LINEAGES OF LIFE
Prokaryotes
Unicellular
Contain cell wall, plasma membrane,
ribosomes, DNA, and cytoplasm
First organisms to inhabit earth
Some are autotrophs and others are
heterotrophs
STRUCTURE AND FUNTION
Three most common shapes
– Cocci – round
– Bacilli – rods
– Helices – spiral
Usually small (1-5μm)
Figure 27.3 The most common shapes of prokaryotes
Prokaryotic cell walls
– Most walls contain peptidoglycan (sugars
cross-linked with polypeptides) except
archaea
– Gram positive – large amounts of
peptidoglycan (stain violet)
– Gram negative – small amounts of
peptidoglycan (stain red)
• Often more threatening due to
lipopolysaccharides on cell walls that are
often toxic
– Antibiotics often inhibit synthesis of
cross-links of peptidoglycan
Figure 27.5 Gram-positive and gram-negative bacteria
Figure 27.5x Gram-positive and gram-negative bacteria
Some have pilli (some for “sex”)
Some have flagella (not covered by
membrane)
Some capable of taxis – movement away
from or toward stimuli
Prokaryotic Genome
– 1/1000 as much DNA
– One circular chromosome (may be
concentrated in a nucleoid region)
– Plasmids – smaller, rings of DNA; may
carry resistance genes, conjugation
genes
Figure 27.6 Pili
REPRODUCTION
Binary fission – cell division; requires
copying the one chromosome and then
cell divides (can happen in 20 minutes)
Genetic recombination – ways that
bacteria can get genes from other
organisms
– Conjugation (bacterial sex)
– Transformation (bacteria grab
foreign DNA from environment)
– Transduction (viruses infect
bacteria with foreign DNA)
Figure 27.x1 Prokaryotic conjugation
Mutation is the main source
of variation in prokaryotes!!
Figure 27.11x1 Cyanobacteria: Gloeothece (top left), Nostoc (top right), Calothrix
(bottom left), Fischerella (bottom right)
DOMAIN ARCHAEA
Prokaryotes
– Methogens – use H2 to reduce CO2
to CH4; poisoned by O2, live in
swamps, decompose sewage, in guts
of animals (cows and termites) help
digest cellulose
– Extreme halophiles – like salt,
purple-red scum due to
bacteriorhodopsin
– Extreme thermophiles – in hot
springs, 60° – 80° C, deep sea vents
at 150° C
Figure 27.14 Extreme halophiles
Figure 27.14x1 Hot springs, home of thermophiles
Figure 27.14x2 Beggiatoa, sulfur-eating bacteria
Figure 27.1 “Heat-loving” prokaryotes