Download Bacteria and Viruses

Bacteria and Viruses
AP Biology
Bacteria Intro
• What do you know about bacteria?
• What do you want to know about bacteria?
• Write down some ideas and then share
with a partner.
Effects of Bacterial Infection
(Tuberculosis)
General Characteristics of
Prokaryotes
• 1 circular double-stranded (ds) DNA and plasmids (small
circular DNA fragments (2-25 genes))
• 4000 genes/4.5 x 106 b.p.
• Reproduction is asexual
• Have a cell wall
• Some have a polysaccharide or protein capsule around
the cell wall
–
–
–
–
Prevents phagocytosis by immune cells
Helps it stick to stuff and each other
Prevents dessication
More virulent (Remember Griffith’s experiment)
• Some have attachment pili – extensions that allow it to
stick to other stuff
Classification
Characteristic
Bacteria
Archaic
Bacteria
Eukaryotes
Nucleus
No
No
Yes
Membrane-bound organelles
No
No
Yes
Ribosomes
Yes
Yes
Yes
Peptidoglycan in cell wall
Yes
No
No
Can live in extreme environments
Yes
No
No
RNA polymerase
One kind
Several kinds Several kinds
DNA
Circular
Circular
Linear
Types of Bacteria
• Gram Positive
– Cell membrane surrounded by a thicker cell
wall made of peptidoglycan (a network of
sugars connected by proteins)
• Gram Negative
– Have a double cell wall
• outer membrane containing lipopolysaccharides
(LPS)
– LPS causes shock, fever, protects it from the immune
system, impedes entry of anti-biotics, etc.
• Thinner layer of peptidoglycan
– Inner cell membrane
Structural Differences
Gram-Negative
• H. influenzae, B. pertussis, H. pylori, etc.
Gram-Positive
• Streptococcus, Staphylococcus, etc.
Penicillin
How do bacteria cause disease
• Make toxins – toxins kill cells
• The lipopolysaccharide (LPS) part of the
cell wall is toxic – released only when the
bacteria die
Varieties
Come in three shapes but
Individual bacteria may aggregate
together in various shapes
• Cocci – spherical
• Bacilli – rod shaped
• Spiral
Bacterial Adaptation
• If unlimited nutrients, can reproduce every 20
minutes – 3 hrs. (usually once per day)
• Some can survive ph 0.3, some heat at 160° F,
high salt environment (typical Archaea)
• In harsh conditions, some can form endospores
– copy their chromosome and surround it with a tough
wall, dehyrdrate themselves and rest of cell
disintegrates – can stay viable for centuries and in
boiling water (ex. Anthrax)
Bacteria are diverse and change and
evolve quickly – if reproduction makes
an exact copy, what accounts for the
diversity?
Genetic Recombination and Diversity
1. Transformation – uptake of DNA from
the surroundings – crossing over occurs
 Usually only between like species
•
specific surface receptors take up DNA
 Can force in the lab with calcium and heat
shock
Bacterial Diversity Continued
2. Transduction – viruses exchange DNA from
1 bacteria to another
•
•
- When a bacteria infecting virus (Phage) leaves it may
take some bacterial DNA with it.
This DNA may get incorporated into the genomes of the
next bacteria infected.
Some Bacteria
DNA in Capsid
Bacterial Diversity Continued
3. Conjugation
“male” attaches to female with sex pili and
send DNA through a cytoplasmic bridge
4. Mutation (9 x 106/day/human host) due to fast
reproduction – 2x1010/day
Plasmids
Plasmids – 2-25 genes
 Copies both directions and can replicate every 20
minutes
 Usually replicates with chromosome
 Can pop in and out of chromosome
 Usually not required for bacterial life
Plasmid Examples
• F plasmid (fertility)
– Genes to make the sex pili
– Thru conjugation gives F plasmid to F– If F plasmid is part of the chromosome, the
whole thing goes and crossing over can occur
• R plasmid (resistance)
– Makes the bacteria antibiotic resistant
– May be resistant to multiple antibiotics
Transposons
• Move from plasmid to chromosome and
back (may just move or copy and then
move)
– Insertion Transposon – transposon includes
information just to cut and move (cut and
paste or copy and paste)
– Complex Transposon – includes other
genes (cut and paste or copy and paste)
– Retrotransposons – makes an RNA copy of
the DNA and uses the RNA to make another
DNA copy that is then inserted somewhere
else (copy and paste)
Getting Food
• Some are photosynthetic
– Have some thylakoid membranes in
cytoplasm (autotroph)
• Some can use chemosynthesis to make
sugars
• Some take in organic molecules from
environment – heterotrophic
• Rare cases uses light but use organic
cmpds instead of CO2 (photoheterotroph)
Energy Usage
• Obligate aerobes – need oxygen to
survive
• Obligate anaerobes – only do fermentation
or use another e- acceptor other than
oxygen (ex: Sulfur)
– Can’t survive in the presence of oxygen
• Facultative anaerobes – can survive with
or without oxygen
Colony formation
• All unicellular but some form colonies
• Bacteria can specialize within the colony
• Some form Biofilms – surface coating
colonies – can send out signals to recruit
more cells
Virus Video
Viruses
Cannot function outside of a host cell except to
attach to another host
Composition
• Genes (4-200 genes) Circular or linear
nucleotides (ds or ss DNA or ds or ss
RNA)
• Capsid (protein coat) – may contain viral
enzymes
• Animal virsuses may have a membrane
envelope (usually created from host
membrane but with viral glycoproteins
sticking out) surrounding the capsid
Virus Structure
Infection
• Specific for certain host cells – usually
tissue and species specific
• In animals - bind to surface receptors on
the host cell and triggers endocytosis
• Viruses that infect bacteria (phages),
usually inject their genes into the cell after
binding to a receptor
• Host cells copy viral genes (uses host’s
DNA polymerase, nucleotides, ribosomes)
• Hosts cells then make viral proteins
• Viruses self-assemble
Phages – Temperate Viruses have Two Phases
Lytic Phase “Virulent”
Host cell dies quickly
Lysogenic Phase
Host lives for awhile
Virus inject DNA
Virus injects DNA
Protein synthesis
Sometimes enzymes that chop up
DNA
Incorporates into host DNA
(Prophage)
Replication of virus DNA
New virus assembly
Burst cell or bleb from cell
releasing new virsues to attach
to other cells
Viral proteins are made that
supress other viral gene
transcription
(virus “hides out” in host)
Host replicates and copies viral
DNA with it
Radiation or stress activates the
virus – it exits the host
chromosome and becomes
lytic
Viral protein synthesis begins
http://www.cat.cc.md.us/courses/bio141/lecguide/unit2/viruses/lytlc.html#rellyt
Viruses that Infect Animal Cells
• Usually have membranes with glycoproteins and
get into the cells via receptors
• Once in, the capsid is removed and they copy
their genomes and make viral proteins
• Viruses fuse with host cell membrane and are
exocytosed taking part of host cell membrane
(viral proteins sticking out)
Polio virus
adenovirus
Oral Herpes
DNA Viruses of Animal Cells
• Herpes – infects nerve cells - when copies
it’s own genome and exits the cells – it
leaves behind copies of its DNA in minichromosomes
• Stress causes them to replicate and form
new viruses
RNA Viruses of Animal Cells
• Some – RNA of virus is used directly as mRNA
so is just translated once inside cell
• Some must copy its RNA to mRNA and replicate
by copying the mRNA – must use its own
enzymes
Retroviruses
• Have reverse transcriptase
• New DNA incorporates as a provirus (never
pops out)
• Uses the hosts RNA polymerase to make its
proteins and to remake itself to be released)
A Closer Look at Retroviruses
Retrovirus Animation
Why are Viruses Bad?
• May kill the cells by chopping up host DNA
or proteins or release lysosomal enzymes
• In bacteria, may burst the cells
• May cause the cells to make toxins
• The envelope proteins may be toxic
themselves
Viral Evolution – Why New
Outbreaks?
• Mutations change viral proteins so they aren’t
recognized by the immune system
– RNA viruses can mutate faster since they aren’t
copied by DNA Polymerase so no proofreading
• Viruses may be able to attach to cells of different
hosts through mutations or exposure to new
species
• Populations may change or come in contact with
viruses new to them
• Environmental changes
Example of Emergent Virus
Viruses and Cancer
• Incorporate into host genome and get cell
to transcribe genes that cause cancer
(oncogenes) or turn on genes in host cell
that cause cancer (proto-oncogenes)
– Usually are growth factor or cell cycle genes
• HPV – cervical cancer
• HTLV - leukemia
Viroids and Prions – mess with
regulartory parts of genes
• Viroids – circular pieces of RNA about 200
nucleotides
• Prions - proteins
Prion Animation