Lecture #10 - Prokaryotic Gene Expression I

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Biology 301 Cellular and Molecular Biology Spring 2002

Lecture # 10: Prokaryotic Gene Expression I Viruses

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Overall outline  Introduction to virology  Bacteriophages  Animal viruses  Prions

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Introduction to Viruses  Size comparisons  Discovery of viruses  Virus structure  Viral structure (detail)

Size comparisons

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Discovery of viruses Tobacco Mosaic Virus

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

• 1883: A. Mayer demonstrated that the disease was contagious and proposed that the infectious agent was an unusually small bacterium not observable under the light microscope. • 1890’s: D. Ivanowsky proposed that the disease was caused by a bacterium that was either too small to be trapped by a filter or that produced a filterable toxin. • 1897: M. Beijerinck proposed that the disease was caused by a reproducing particle much smaller and simpler than a bacterium. • 1935: W.M. Stanley crystallized the infectious particle now known as tobacco mosaic virus (TMV).

Virus structure

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Three possible patterns of viral genome replication • DNA -> DNA • RNA -> RNA (with RNA replicase) • RNA -> DNA -> RNA (with reverse transcriptase)

Viral structure (detail)

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Bacteriophages  Bacteriophages  Hershey-Chase experiment revisited  Simplified virus life cycle  A simplified viral reproductive cycle  The lytic cycle of phage T4  The lysogenic and lytic reproductive cycles of phage lambda

Bacteriophages Bacteriophages are viruses that specifically infect bacteria. Though not medically important, they have served as a useful experimental system for the study of basic genetic and biochemical mechanisms.

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Hershey-Chase experiment revisited

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Simplified virus life cycle • Several steps are involved in viral infection and propagation. • The adsorption step determines tissue specificity and is also the point at which many antibodies neutralize viral infection. • Upon entering the host cell infection can lead to several different outcomes: lysis (adenovirus, influenza, poliovirus), persistence (hepatitis B, Epstein-Barr virus) latency (herpesvirus) or transformation (hepatitis B, Epstein-Barr)

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

A simplified viral reproductive cycle

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

The lytic cycle of phage T4

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

The lysogenic and lytic reproductive cycles of phage lambda

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Animal viruses  Classes of animal viruses  The reproductive cycle of an enveloped retrovirus virus  HIV, a retrovirus  HIV infection

Classes of animal viruses

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

The reproductive cycle of an enveloped retrovirus virus

(Reverse transcription)

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

HIV, a retrovirus

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

HIV infection

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

1.  HIV specifically infects T­helper cells.  The Epstein­Barr virus specifically infects B­cells.  What accounts for this specificity? 2.  The HIV envelope contains within it two embedded membrane proteins: gp120 and gp41.  What are the functions of each?

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Prions  Prions defined  Prion replication

Prions defined • Prions are small, proteinaceous infectious particles that resist inactivation by procedures which affect nucleic acids. • To date, no detectable nucleic acids of any kind and no viruslike particles have been associated with prions. • Prions cause scrapie and other spongiform encephalopathies of animals and humans

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University

Prion replication

Ogan Gurel, MD Biology 301 Lecture # 10 Roosevelt University