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 aggregatetogether 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

1.1. TransformationTransformation – 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

2.2. TransductionTransduction – 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

3.3. ConjugationConjugation“male” attaches to female with sex pili and send DNA through a cytoplasmic bridge

4.4. MutationMutation (9 x 106/day/human host) due to fast reproduction – 2x1010/day

Plasmids

PlasmidsPlasmids – 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)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)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 TransposonInsertion Transposon – transposon includes

information just to cut and move (cut and paste or copy and paste)

– Complex TransposonComplex 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

VirusesCannot function outside of a host cell except to

attach to another host

CompositionComposition• 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

InfectionInfection• 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

Virus inject DNA

Protein synthesisSometimes enzymes that chop up

DNA

Replication of virus DNA

New virus assembly

Burst cell or bleb from cell releasing new virsues to attach

to other cells

Lysogenic PhaseHost lives for awhile

Virus injects DNA

Incorporates into host DNA (Prophage)

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)

adenovirusadenovirusOral HerpesOral Herpes

Polio virusPolio virus

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 mini-chromosomes

• 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