Transcript Document
What are prokaryotic cells? • Single-celled bacteria and archaeans • No nucleus or membrane-bound organelles • Smallest, most widely distributed, numerous, and metabolically diverse organisms – Autotrophs and heterotrophs • Spheres (cocci), rods (bacilli), spirals (spirilla) How does the structure look? • Typical surface structures – Cell wall – Outermost protective capsule or slime layer – One or more flagella – Pili How do Prokaryotes Reproduce? • Only bacteria and archaeans reproduce by prokaryotic fission: – Replication of single, circular prokaryotic chromosome – Division of parent cell into two genetically equivalent daughter cells • Horizontal gene transfers can move genes between prokaryotes • Conjugation moves a plasmid and some chromosomal genes into another cell through a sex pilus What are the bacteria? • The most common and diverse prokaryotes – Some are pathogens (cause disease in a host) Bacterial Diversity: Cyanobacteria • Oxygen-releasing photoautotrophs – Chloroplasts probably evolved from ancient cyanobacteria by endosymbiosis Bacterial diversity: proteobacteria • The most diverse bacterial group – Include autotrophs and heterotrophs, free-living species, beneficial symbionts, and pathogens – Example: Thiomargarita namibiensis – Bacterial are divided into two classes or groups • Gram Positive • Gram negative What are gram-positive bacteria ? • Have thick walls – Endospores resist heat, boiling, irradiation, acids and disinfectants – Some are human pathogens • Chlamydias What are spirochetes? • Spring-shaped – Live on their own or in hosts – Some are pathogens What are the archaeans? • Archaeans are prokaryotic, but like eukaryotic cells in certain features – Halophiles (salt lovers), extreme thermophiles, and methanogens (methane makers) • Comparisons of structure, function, and genetic sequences put archaeans in a separate domain, between eukaryotes and bacteria • Archaeans are more diverse and widely distributed than previously thought What are the viruses? • Viruses are noncellular infectious particles that cannot reproduce on their own • Viruses infect a host cell; their genes and enzymes take over the host’s mechanisms of replication and protein synthesis Virus infections Virus Structure • A virus particle consists of a core of DNA or RNA and a protein coat • In some viruses, the coat is enveloped in some of an infected cell’s plasma membrane – Outer envelope forms as each new virus particle is released by budding or lysis • In bacteriophages and other complex viruses, the coat has a sheath and other structures Viral Multiplication Pathways • Multiplication pathways vary greatly • Two are common among bacteriophages – Lytic pathway – Lysogenic pathway Lytic Pathway • New virus particles are released by lysis – Multiplication is rapid Lysogenic Pathway • Virus enters a latent state that extends the cycle – Host cell is not killed outright • Viral nucleic acids integrate into host chromosome – All host cell’s descendants inherit genetic material – May be reactivated many generations later, causing cell to enter lytic pathway What are prion infections? Prions are infectious misfolded versions of normal proteins How do pathogens evolve? • Pathogens evolve to not kill a host before they can infect other host individuals • Use of antibiotics favors antibiotic-resistant bacteria • Genes that convey drug resistance can arise by mutation, may spread among members of the same or different species by conjugation • Diseases can be fatal – If an individual becomes host to multiple pathogens – If an individual has no coevolved defenses – If a pathogen mutates into a different form that can breach current defenses • Two deadly emerging pathogens – Ebola and the H5N1 strain of bird flu