Chapter 21: Prokaryotes & Viruses

Chapter 21: Prokaryotes & Viruses

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

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

The Prokaryotes Archaebacteria and Eubacteria Arose before the eukaryotes

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

Prokaryotic Body Plan cytoplasm, with ribosomes DNA, in nucleoid pilus bacterial flagellum outer capsule cell wall plasma membrane Fig. 21-2, p.334

Bacterial Shapes coccus bacillus spirillum p. 334

Bacterial Shapes Fig. 21-3a, p.335

Bacterial Shapes Fig. 21-3b, p.335

Bacterial Shapes Fig. 21-3c, p.335

Metabolic Diversity Photoautotrophs Chemoautotrophs Chemoheterotrophs

Gram Stain Fig. 21-4, p.335

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

Bacterial Reproduction Binary fission (splitting into 2) is a type of asexual reproduction Conjugation is a type of sexual reproduction

Prokaryotic Fission Fig. 21-5, p.335

Stepped Art Fig. 21-5, p.335

bacterial chromosome Bacterium before DNA replication DNA replication begins parent DNA molecule DNA copy DNA replication completed Stepped Art Fig. 21-5a-c, p.336

Membrane growth moves DNA molecules apart New membrane and cell-wall material deposited Cytoplasm divided in two Stepped Art Fig. 21-5d-f, p.336

Conjugation Transfer of plasmid Fig. 21-6, p.337

nicked plasmid conjugation tube Stepped Art Fig. 21-6, p.337

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

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

Eubacterial Diversity Fig. 21-7a, p.338

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

resting spore Some Pathogenic Eubacteria photosynthetic cell heterocyst Fig. 21-8a, p.339

Some Pathogenic Eubacteria Fig. 21-8b, p.339

Some Pathogenic Eubacteria Fig. 21-8c, p.339

Some Pathogenic Eubacteria DNA spore coat capsule around cell wall Fig. 21-8d, p.339

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 Fig. 21-9, p.339

Archaebacteria Fig. 21-10, p.340

Archaebacteria Methanogens Extreme halophiles Extreme thermophiles

Methanogens Fig. 21-11a, p.340

Methanogens Fig. 21-11b, p.340

Extreme Halophiles Fig. 21-12a, p.341

Extreme Thermophiles

Viral Body Plans Complex virus (bacteriophage) Genetic material is DNA or RNA Coat is protein Helical virus Polyhedral virus Fig. 21-13, p.342

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

Enveloped Virus (HIV) viral protein lipid envelope (derived from host) viral RNA viral coat (proteins) reverse transcriptase Fig. 21-13, p.342

viral RNA Enveloped Virus (HIV) protein subunits of coat 18 nm diameter, 250 nm length Fig. 21-13a, p.342

Enveloped Virus (HIV) 80 nm diameter Fig. 21-13b, p.342

Enveloped Virus DNA (HIV) protein coat sheath base plate tail fiber Fig. 21-13c, p.342

viral coat (proteins) Enveloped Virus (HIV) reverse transcriptase 100-120 nm diameter viral RNA lipid envelope: proteins span the envelope, line its inner surface, spike out above it Fig. 21-13d, p.342

Viruses Fig. 21-14a, p.343

Viruses Fig. 21-14b, p.343

Viruses Fig. 21-14d, p.343

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

Lytic e Lysis of host cell is induced; infectious particles escape. Pathway Lytic Pathway d The coats get tail fibers, other parts. 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. Lysogenic Pathway a-4 Viral DNA is excised from the chromosome. 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.

Lytic Pathway Fig. 21-15a, p.344

Lytic Lysis of host cell is induced; infectious particles escape. 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. Stepped Art Fig. 21.20

Lysogenic Pathway Viral DNA usually becomes integrated into the bacterial chromosome. 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. Stepped Art Fig 21.20 (2)

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

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 p.346a

SARS virus p.346b