BIOL 3340 Chapter 5

Viruses & Other Acellular Agents Other Acellular Agents

Viruses Viruses: are noncellular or Acellular infectious agents Virology: study of viruses Virologists: scientists who study viruses

General features of Viruses Viruses are infectious agents with both living and nonliving characteristics. Viruses are infectious agents with both living and nonliving characteristics. 1. Living characteristics of viruses a. They reproduce at a fantastic rate, but only in living host cells. a. They reproduce at a fantastic rate, but only in living host cells. b. They can mutate. b. They can mutate.

…General features of Viruses 2. Nonliving characteristics of viruses a. They are acellular, that is, they contain no cytoplasm or cellular organelles. a. They are acellular, that is, they contain no cytoplasm or cellular organelles. b. They carry out no metabolism on their own and must replicate using the host cell's metabolic machinery. b. They carry out no metabolism on their own and must replicate using the host cell's metabolic machinery.

virus particles contains either DNA or RNA (not both) virus particles contains either DNA or RNA (not both) Nucleic Acid is surrounded or coated by a protein shell (capsid) Nucleic Acid is surrounded or coated by a protein shell (capsid) Some viruses possess a membrane-like envelope surrounding the particle Some viruses possess a membrane-like envelope surrounding the particle …General features of Viruses

…General Properties of viruses consists of  1 molecule of DNA or RNA enclosed in coat of protein consists of  1 molecule of DNA or RNA enclosed in coat of protein may have additional layers may have additional layers cannot reproduce independent of living cells nor carry out cell division as procaryotes and eucaryotes do cannot reproduce independent of living cells nor carry out cell division as procaryotes and eucaryotes do

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8 The Size and Morphology of Selected Viruses Figure 5.2

Generalized Structure of Viruses

The Structure of Viruses Virion size range is ~ nm Virion size range is ~ nm All virions contain a nucleocapsid which is composed of nucleic acid (DNA or RNA) and a protein coat (capsid) All virions contain a nucleocapsid which is composed of nucleic acid (DNA or RNA) and a protein coat (capsid) some viruses consist only of a nucleocapsid, others have additional components some viruses consist only of a nucleocapsid, others have additional components Envelopes Envelopes virions having envelopes = enveloped viruses virions having envelopes = enveloped viruses virions lacking envelopes = naked viruses virions lacking envelopes = naked viruses

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 11 Capsids large macromolecular structures which serve as protein coat of virus large macromolecular structures which serve as protein coat of virus protect viral genetic material and aid in its transfer between host cells protect viral genetic material and aid in its transfer between host cells made of protein subunits called protomers made of protein subunits called protomers

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 12 Helical Capsids-Tobacco Mosaci Virus shaped like hollow tubes with protein walls shaped like hollow tubes with protein walls

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13 Influenza Virus – an Enveloped Virus with a Helical Nucleocapsid Figure 5.4

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14 Attachment Receptor sites: specific surface structures on host to which viruses attach specific surface structures on host to which viruses attach specific for each virus specific for each virus can be proteins, lipopolysaccharides, techoic acids, etc. can be proteins, lipopolysaccharides, techoic acids, etc.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 15 Entry into the Host most bacterial viruses (bacteriophages) inject their nucleic acid into host most bacterial viruses (bacteriophages) inject their nucleic acid into host eucaryotic viruses usually enter the cytoplasm with the genome still enclosed. eucaryotic viruses usually enter the cytoplasm with the genome still enclosed.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16 Figure 5.8

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17 Fusion with Host Membrane Figure 5.12 (a)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18 Generalized Illustration of Virus Reproduction Figure 5.11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 19 Figure 5.22

Top ten Infectious diseases 0geu510a4tJJPoAS8VXNyoA?p=list+of+ deadly+virus&y=Search&fr=yfp-t-501-s 0geu510a4tJJPoAS8VXNyoA?p=list+of+ deadly+virus&y=Search&fr=yfp-t-501-s 0geu510a4tJJPoAS8VXNyoA?p=list+of+ deadly+virus&y=Search&fr=yfp-t-501-s 0geu510a4tJJPoAS8VXNyoA?p=list+of+ deadly+virus&y=Search&fr=yfp-t-501-s Assignment: Ebola, Cholera, Shanti, AIDS, West Nile, Small pox, Birds Flu. Assignment: Ebola, Cholera, Shanti, AIDS, West Nile, Small pox, Birds Flu.

Bibliography d d d d o3340/home.html o3340/home.html o3340/home.html o3340/home.html Lecture PowerPoints Prescott’s Principles of Microbiology-Mc Graw Hill Co. Lecture PowerPoints Prescott’s Principles of Microbiology-Mc Graw Hill Co. guide/unit3/viruses/ssvir.html guide/unit3/viruses/ssvir.html