Lecture 27 _March 16_ Viruses post

Lecture 27 _March 16_ Viruses post - Biology 171 Lecture...

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1 Lecture 27: Wednesday March 16, 2011 Biology 171 Today’s Topic: Viruses Announcements This Week in Discussion: Cichlid Evolution & Speciation Text Reading Chapter 35 (675-692) Characteristics of Viruses - morphology - nature of genetic material Diversity of Viruses - lytic & lysogenic cycles - influenza - retroviruses & HIV - smallpox Origin of Viruses Viruses – Who Cares? • Viruses are ubiquitous disease-causing agents that influence ecological and evolutionary processes • They attack humans (e.g. flu, AIDS, herpes) • They attack our crops, our livestock and our pets, causing billions of dollars in damage annually (e.g. barley yellow dwarf virus) Viruses are tiny, noncellular particles that infect virtually every type of cell known. All viruses are obligate parasites. They cannot perform metabolism on their own—meaning outside a parasitized cell— and are not considered to be alive. Because they are not organisms, viruses are referred to as particles or agents and are not given scientific names. Different types of viruses are specialized for infecting particular host species and types of cells – they recognize host cells by their unique glycoproteins Viruses are noncellular, obligate intracellular parasites. Obligate means that viruses cannot replicate unless they enter a host cell. Viruses are ubiquitous and abundant.
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2 Virus-Infected Pumpkins Barley Yellow Dwarf Virus (on Oats) Tomato Yellow Leaf Curl Virus Gypsy Moth Nuclear Polyhedrosis Virus Viruses are highly diverse in overall morphology and in the nature of their genetic material. Viruses are noncellular, thus they cannot synthesize ATP and are not capable of transcription (making mRNA) or translation (synthesizing proteins) until they get inside a host cell and hijack its cellular machinery to carry out these functions. Viruses are highly diverse in overall morphology and in the nature of their genetic material. Nature of genetic material - several possibilities: DNA (single stranded or double stranded) RNA (single stranded or double stranded)
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3 Enveloped viruses are released from the host cell encapsulated in the latter’s cell membrane – why might this be advantageous for the virus? The viral infection cycle can be broken down into five steps: Viruses leave a host cell by budding from the cell membrane or by bursting out of the cell All viruses undergo lytic growth, but some types of viruses also grow lysogenically, integrating into the host’s genome and initiating lytic growth at some later time. Why is this significant? Smallpox – an infectious disease that resulted in millions of human deaths throughout human history Smallpox is contracted through inhaling the virus and causes skin eruptions called papules (elevated bumps) and pustules (bumps containing fluid). An infected person is only contagious AFTER the skin eruptions have started. The disease usually runs a course of two weeks, punctuated by high fever both prior to and
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This note was uploaded on 04/24/2011 for the course BIOLOGY 171 taught by Professor Hunter during the Winter '09 term at University of Michigan.

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Lecture 27 _March 16_ Viruses post - Biology 171 Lecture...

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