Prokaryotes and Viruses

West Nile Virus

West Nile Virus One of several mosquito-borne viruses in the United States that can infect people The virus exists in nature primarily through a transmission cycle involving mosquitoes and birds. Mosquitoes become infected with West Nile virus (WNV) when they feed on infected birds

West Nile Virus Symptoms Majority of people that become infected with the West Nile virus have no illness or experience only a mild flu-like illness May include fever, headache and body aches lasting only a few days Some persons may also have a mild rash or swollen lymph glands Less than one percent of those infected may develop meningitis or encephalitis, the most severe forms of the disease

How Long has the West Nile Virus Been Around? Alexander the Great, 336 B.C., conquered a vast empire It’s speculated that his demise was due to West Nile encephalitis There is still no human vaccine for West Nile virus

West Nile Virus Takes Off West Nile Virus is pathogenic, it invades its host and multiplies, causing disease It’s a flavivirus, traveling inside mosquitoes which act as the transferring agent from host to host

West Nile Virus Takes Off

West Nile Virus Takes Off

West Nile Virus Takes Off Impacts, Issues Video West Nile Virus Takes Off

Microorganisms Single-celled organisms that are too small to be seen without a microscope Bacteria are the smallest living organisms Viruses are smaller but are not alive

The Prokaryotes Only two groups Archaebacteria and Eubacteria Arose before the eukaryotes

Prokaryotic Characteristics No membrane-bound nucleus Single chromosome Cell wall (in most species) Prokaryotic fission Metabolic diversity

Prokaryotic Body Plan DNA capsule plasma membrane ribosomes in cytoplasm bacterial flagellum pilus cell wall cytoplasm

cytoplasm, with ribosomes Prokaryotic Body Plan cytoplasm, with ribosomes DNA, in nucleoid pilus bacterial flagellum outer capsule cell wall plasma membrane

Prokaryotic Body Plan Prokaryotic body plan

Bacterial Shapes coccus bacillus spirillum

Bacterial Shapes

Bacterial Shapes

Bacterial Shapes

Bacterial Shapes sex pilus

Metabolic Diversity Photoautotrophs Chemoautotrophs Chemoheterotrophs

Gram Stain

Gram Stain Gram stain

Bacterial Genes Bacteria have a single chromosome Circular molecule of DNA Many bacteria also have plasmids Self-replicating circle of DNA that has a few genes Can be passed from one cell to another

Prokaryotic Fission

Prokaryotic Fission

Prokaryotic Fission

Prokaryotic Fission

Prokaryotic Fission

Prokaryotic Fission

Prokaryotic Fission

Prokaryotic Fission

DNA replication begins DNA replication completed Bacterium before DNA replication bacterial chromosome DNA replication begins parent DNA molecule DNA copy DNA replication completed

Membrane growth moves DNA molecules apart New membrane and cell-wall material deposited Cytoplasm divided in two

Prokaryotic Fission - 3 Prokaryotic fission

Conjugation Transfer of plasmid

nicked plasmid conjugation tube

Prokaryotic conjugation

Prokaryotic Classification EUBACTERIA (Bacteria) ARCHAEBACTERIA (Archaea) EUKARYOTES (Eukarya) Traditionally classified by numerical taxonomy Now increased use of comparative biochemistry

Prokaryotic Classification to ancestors of eukaryotic cells DOMAIN BACTERIA DOMAIN BACTERIA biochemical and molecular origin of life

Eubacteria Includes most familiar bacteria Have fatty acids in plasma membrane Most have cell wall; always includes peptidoglycan Classification based largely on metabolism

Eubacterial Diversity Photoautotrophic Aerobic (Cyanobacteria) Anaerobic (Green bacteria) Chemoautotrophic Important in nitrogen cycle Chemoheterotrophic Largest group

Examples of eubacteria

Eubacterial Diversity

Eubacterial Diversity

Eubacterial Diversity

Some Pathogenic Eubacteria Most are chemoheterotrophs E. coli strains Clostridium botulinum Clostridium tetanus Borrelia burgdorferi Rickettsia rickettsii

Some Pathogenic Eubacteria resting spore photo-synthetic cell heterocyst

Some Pathogenic Eubacteria

Some Pathogenic Eubacteria

Some Pathogenic Eubacteria DNA spore coat capsule around cell wall

Bacterial Behavior Bacteria move toward nutrient-rich regions Aerobes move toward oxygen; anaerobes avoid it Photosynthetic types move toward light Magnetotactic bacteria swim downward Myobacteria show collective behavior

Bacterial Behavior

Archaebacteria

Archaebacteria Methanogens Extreme halophiles Extreme thermophiles

Methanogens

Methanogens

Extreme Halophiles

Extreme Thermophiles

Extreme Thermophiles

Virus Noncellular infectious agent Protein wrapped around a nucleic acid core Cannot reproduce itself; can only be reproduced using a host cell

Viral Body Plans Genetic material is DNA or RNA Coat is protein Complex virus (bacteriophage) Genetic material is DNA or RNA Coat is protein Helical virus Polyhedral virus

Enveloped Virus (HIV) viral protein lipid envelope (derived from host) viral RNA reverse transcriptase viral coat (proteins)

Enveloped Virus (HIV) viral RNA protein subunits of coat 18 nm diameter, 250 nm length

Enveloped Virus (HIV) 80 nm diameter

Enveloped Virus (HIV) 65–nm diameter head, 225 nm total length DNA protein coat sheath base plate tail fiber

Enveloped Virus (HIV) viral coat (proteins) reverse transcriptase 100-120 nm diameter viral RNA lipid envelope: proteins span the envelope, line its inner surface, spike out above it

Viral Body Plans Body plans of viruses

Viruses

Viruses

Viruses

Viruses

Viral Multiplication - Basic Steps Attach to host cell Enter host (virus or just genetic material) Direct host to make viral genetic material and protein Assemble viral nucleic acids and proteins Release new viral particles

Bacteriophage multiplication cycles Viral Replication Bacteriophage multiplication cycles

e Lysis of host cell is induced; infectious particles escape. Lytic Pathway d The coats get tail fibers, other parts. Lytic Pathway a Virus particle injects genetic material into a suitable host cell after binding to its wall. c Viral proteins are assembled into coats around viral DNA. b Viral DNA directs host cell to make viral proteins and replicate viral DNA. a-1 Viral DNA is integrated into the host’s chromosome. a-4 Viral DNA is excised from the chromosome. Lysogenic Pathway a-2 Before prokaryotic fission, the bacterial chromosome with the integrated viral DNA is replicated. a-3 After cell division, each daughter cell will have recombinant DNA. Fig. 21-15, p.344

Lytic Pathway

Lysis of host cell is induced; infectious particles escape. Lytic Pathway Tail fibers and other parts are added to coats. Virus particles bind to wall of suitable host. Viral genetic material enters cell cytoplasm. Viral protein molecules are assembled into coats; DNA is packaged inside. Viral DNA directs host machinery to produce viral proteins and viral DNA.

Lytic Pathway Lytic pathway

Viral DNA usually becomes integrated into the bacterial chromosome. Lysogenic Pathway Viral DNA is excised from chromosome and cell enters lytic pathway. Prior to prokaryotic fission, the chromosome and integrated viral DNA are replicated. After binary fission, each daughter cell will have recombinant DNA.

Lysogenic Pathway Lysogenic pathway

Replication of an Enveloped Virus DNA virus particle plasma membrane of host cell Transcription of viral DNA Replication of viral DNA Translation nuclear envelope some proteins for viral coat viral DNA other proteins for viral envelope

Replication of an Enveloped Virus

Replication of an Enveloped Virus Enveloped DNA virus replication

Nature of Disease Contagious disease pathogens must directly contact a new host Epidemic Pandemic (AIDS) Sporadic Endemic

Evolution and Disease Host and pathogen are coevolving If a pathogen kills too quickly, it might disappear along with the individual host Most dangerous if pathogen Is overwhelming in numbers Is in a novel host Is a mutant strain

Mycobacterium tuberculosis

SARS virus

New Threats Emerging Pathogens Drug-resistant strains Food poisoning Ebola virus Monkeypox virus SARS virus Drug-resistant strains Food poisoning E. coli Salmonella

Viroids Smaller than viruses Strands or circles of RNA No protein-coding genes No protein coat Cause many plant diseases

Prions Small proteins Linked to human diseases Animal diseases Kuru Creutzfeldt-Jakob disease (CJD) Animal diseases Scrapie in sheep Bovine spongiform encephalopathy (mad cow disease)