what are prokaryotic cells? single-celled bacteria and archaeans no nucleus or membrane-bound...

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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)

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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 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