Viruses and Bacteria

Pathogen Any living organism or particle that can cause an infectious disease

Virus vs. Bacteria A virus is an infectious particle made only of a strand of DNA or RNA surrounded by a protein coat. Bacteria are one-celled microorganisms that can also cause infection.

Viruses

Are viruses living things? Characteristics of Living Things: – Reproduce, use nutrients and energy, grow and develop, respond to their environment and made of genes

Are viruses living things? Viruses: – Respond to their environment – Made of genes – Can reproduce but NOT ON THEIR OWN Require living things to help them reproduce and make proteins Viral Replication-virus invades healthy cell, when cell divides the virus is passed to the daughter cells Virus can also replicate inside a host cell and cause the cell to burst, which releases new viruses. THEY ARE NOT LIVING ORGANISMS!!!!!!

Viral Structure Viruses have a simple structure. – genetic material – capsid, a protein shell – maybe a lipid envelope, a protective outer coat Capsid give viruses a variety of shapes: – Enveloped – Helical – Polyhedral

capsid DNA tail sheath tail fiber

Viruses enter host cell in different ways: Bacteriophages pierce host cells – Viruses that prey on bacteria – Example: Escherichia coli Viruses of eukaryotes enter by endocytosis Viruses of eukaryotes also fuse with membrane

Viral Diseases Some viral diseases can be prevented with vaccines. – Substance that stimulates the body’s own immune response against invasion by microbes. There are many examples of viral infections: – common cold – Influenza – SARS – HIV The body has natural defenses against viruses but viral diseases can be hard to cure because: – viruses replicate quickly – some viruses mutate

Bacteria Kingdom Eubacteria and Kingdom Archaebacteria

Bacteria and Archaea (Prokaryotes) The most widespread and abundant organisms on Earth. Live in just about every habitat on Earth, including the air.

Grouped based on need for oxygen: Obligate anaerobe-cannot live in the presence of oxygen Obligate aerobes-require oxygen in their environment Facultative aerobe-can live with or without oxygen

Kingdom Eubacteria (true bacteria) Unicellular Prokaryotes Cell walls made of peptidoglycan Include both autotrophs and heterotrophs Classified by shape: – Coccus – Bacillus – Spirillum Example: E. coli bacteria-found in your intestine and helps you digest food.

Kingdom Archaebacteria Unicellular Prokaryotes Do not have peptidoglycan in their cell walls Includes both autotrophs and heterotrophs Can live in extreme environments – Very hot or cold – Water with high salt concentrations – Deep ocean water Archaebacteria that live here are autotrophs, they make their food through chemosynthesis

Eubacteria and Archaea Structural Similarities Small Single-celled Cell walls Plasma membranes Lack a nucleus (Prokaryotes) and other membrane bound organelles Plasmids-small piece of genetic material that can replicate Flagellum used for locomotion Pili-help prokaryotes stick to surfaces and other prokaryotes

flagellum pili plasmid cell wall chromosome plasma membrance This diagram shows the typical structure of a prokaryote. Archaea and bacteria look very similar, although they have important molecular differences.

Eubacteria and Archaea have molecular differences: Archaea contain lipids that are not found in any other type of organism Bacteria have a polymer called peptidoglycan in their cell walls, archaea do not! Differences in RNA Because of these differences bacteria and archaea are not closely related.