what are prokaryotic cells? single-celled bacteria and archaeans no nucleus or membrane-bound...
TRANSCRIPT
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 aregram-positive bacteria ?
• Have thick walls– Endospores resist
heat, boiling, irradiation, acids and disinfectants
– Some are human pathogens• Chlamydias
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
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
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