Microbial Biotechnology Lecture:2 Microbial Biotechnology

Microbes can be classified into four major groups: 1- Viruses 2- Bacteria 3- Fungi 4- Protozoa

1- Viruses

Introduction to Viruses Obligate Intracellular Parasite

Virion Structure Lipid Envelope Nucleic Acid Protein Capsid Virion Spike Projections Protein Capsid Lipid Envelope Virion Associated Polymerase ·         This overhead shows the standard features found in some (but not all) viruses. ·         A virus particle is essentially a piece of nucleic acid surrounded by a protein coat. ·         The protein coat (i.e. the capsid) is a delivery system for transferring the virus genome from one cell to another. The protein serves to: Ø     Provide protection to the nucleic acid against the environment - e.g. nucleases etc. Ø     Function in receptor recognition - targeting a virus to a susceptible host and cell type. ·         Surrounding this coat there may be a lipid envelope - this envelope is derived from one of the cell membranes and is not determined by the virus. There may be some modification to the lipid composition induced during virus maturation. ·         Inserted into the lipid envelope there are usually virus proteins which are present as spike projections - these are normally glycoproteins. Due to restrictions on the coding size of many virus genomes the capsid of the virion is made up of repeating subunits, which coat the virus genomic nucleic acid. The redundancy also allows for the fact that if there is an inactivation of part of the capsid the virus does not completely lose its infectivity For example the poliovirus RNA (7kb) can specific at most 250,000 Daltons of protein altogether (some must be used for replication) but the poliovirus virion capsid weighs 6 x 106 Daltons. Genomic Nucleic Acid Viruses only possess a single type of genomic nucleic acid – either DNA or RNA but not both. This nucleic acid can be in a variety of physicla forms that can be used as a valuable classification feature.

copyright cmassengale Characteristics Viral capsids (coats) are made of individual protein subunits Individual subunits are called capsomeres CAPSOMERES copyright cmassengale

copyright cmassengale Discovery of Viruses Beijerinck (1897) coined the Latin name “virus” meaning poison. He studied filtered plant juices & found they caused healthy plants to become sick. copyright cmassengale

Tobacco Mosaic Virus Wendell Stanley (1935) crystallized sap from sick tobacco plants He discovered viruses were made of nucleic acid and protein

Smallpox Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses Deadly viruses are said to be virulent Smallpox has been eradicated in the world today

Morphology of viruses

Viral Shapes There are 3 different shapes of Virus Helical Icosahedral (Tobacco mosaic virus) Complex (Bacteriophage – a virus which infects bacteria) Icosahedral (Influenza)

Viral Properties Viruses are inert (nucleoprotein ) filterable Agents. Viruses cannot make energy or proteins independent of a host cell. Viral genome are RNA or DNA but not both. Some viruses contain proteins with enzymatic functions that are needed for genome They are very small in size, from 20-300 m. They are unaffected by antibiotics. They are sensitive to interferon.

Are viruses alive? No Yes They are not made of cells or organelles They cannot reproduce without a host They do not metabolize energy They do not perform cellular processes Reproduce They have DNA or RNA They can adapt to surroundings The have organization

copyright cmassengale Chickenpox Virus copyright cmassengale

Viruses that attack bacteria are called bacteriophage or just phage T-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails HOST specific

Diagram of T-4 Bacteriophage Head with 20 triangular surfaces Capsid contains DNA Head & tail fibers made of protein