Presentation on theme: "Prokaryotes and Viruses Chapter 21. Microorganisms Single-celled organisms that are too small to be seen without a microscope Bacteria are the smallest."— Presentation transcript:
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
Prokaryotic Fission - 1 DNA replication begins Bacterium before DNA replication bacterial chromosome Figure 21.7 Page 350
Prokaryotic Fission - 2 parent DNA molecule DNA copy DNA replication completed Membrane growth moves DNA molecules apart Figure 21.7 Page 350
Prokaryotic Fission - 3 New membrane and cell-wall material deposited Cytoplasm divided in two Figure 21.7 Page 350
Conjugati on nicked plasmid in donor cell conjugation tube to recipient cell Transfer of plasmid Figure 21.8 Page 351
Prokaryotic Classification EUBACTERIA (Bacteria) ARCHAEBACTERIA (Archaea) EUKARYOTES (Eukarya) Traditionally classified by numerical taxonomy Now increased use of comparative biochemistry Figure 21.9 Page 351
Virus Noncellular infectious agent Protein wrapped around a nucleic acid core Cannot reproduce itself; can only be reproduced using a host cell
Viral Body Plans Genetic material is DNA or RNA Coat is protein Complex virus (bacteriophage) Polyhedral virusHelical virus Fig. 21.18 Page 356
Enveloped Virus (HIV) Fig. 21.18 Page 356 lipid envelope (derived from host) viral RNA reverse transcriptase viral coat (proteins) viral protein
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 Pathway Stepped Art Fig. 21.20 Page 358 Virus particles bind to wall of suitable host. Viral genetic material enters cell cytoplasm. Viral DNA directs host machinery to produce viral proteins and viral DNA. Viral protein molecules are assembled into coats; DNA is packaged inside. Tail fibers and other parts are added to coats. Lysis of host cell is induced; infectious particles escape.
Lysogenic Pathway Stepped Art Fig 21.20 (2) Page 358 Viral DNA usually becomes integrated into the bacterial chromosome. Prior to prokaryotic fission, the chromosome and integrated viral DNA are replicated. After binary fission, each daughter cell will have recombinant DNA. Viral DNA is excised from chromosome and cell enters lytic pathway.
Replicatio n of an Enveloped Virus viral DNA some proteins for viral coat Replication of viral DNA DNA virus particle plasma membrane of host cell nuclear envelope other proteins for viral envelope Translation Transcription of viral DNA Figure 21.21 Page 359
Viroids Smaller than viruses Strands or circles of RNA No protein-coding genes No protein coat Cause many plant diseases
Prions Small proteins Linked to human diseases Kuru Creutzfeldt-Jakob disease (CJD) Animal diseases Scrapie in sheep Bovine spongiform encephalopathy (mad cow disease)
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
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