COURSE DESCRIPTION

The nuclear genomes of eukaryotes differ greatly in size, number of genes and density from one another. The number of chromosomes differs between species and, in addition, certain organelles in eukaryotes possess small amounts of their own DNA. Eukaryotic genomes generally have a higher proportion of non-coding DNA to coding DNA. In addition to a large, circular chromosome, bacteria also have several plasmids. Even though bacteria reproduce asexually, they exhibit a great deal of genetic diversity through mutation and genetic transfer. In contrast to eukaryotic and prokaryotic genomes, the viral genome varies according to the type of virus: the genome may be DNA or RNA in nature and single – or double-stranded. For RNA viruses, they may possess either positive-sense RNA (i.e. identical to viral mRNA and thus can be immediately translated) or negative-sense RNA (i.e. complementary to viral mRNA and thus must be converted to positive-sense RNA by RNA polymerase before translation).

LEARNING OUTCOMES

Candidates should be able to:

• Outline the cell theory with the understanding that cells are the smallest unit of life, all cells come from pre-existing cells and living organisms are composed of cells.
• Describe the structural components of viruses, including enveloped viruses and bacteriophages, and interpret drawings and photographs of them
• Discuss how viruses challenge the cell theory and concepts of what is considered living
• Describe the structure and organisation of viral, prokaryotic and eukaryotic genomes (including DNA/RNA, single/double-stranded, number of nucleotides, packing of DNA, linearity/circularity and presence/absence of introns)
• Describe how the genomes of viruses are inherited through outlining the reproductive cycles of:

1. bacteriophages that reproduce via a lytic cycle only, including T4 phage
2. bacteriophages that reproduce via lytic and lysogenic cycles, including lambda phage
3. enveloped viruses, including influenza
4. retroviruses, including HIV

• Describe how variation in viral genomes arises, including antigenic shift and antigenic drift

Use the knowledge gained in this topic in novel situation to solve related problems.

Lecture Outline

Overview of Topic               

1. What is a Virus?
   • Viruses are Obligate Intracellular Parasites
   • Are Viruses Living or Non-living Organisms?

2. General Structure of Viruses

2.1 Structure and Organisation of Viral Genome                                                              

2.2 Capsid – present in ALL viruses                                                              

2.3 Envelope – present in ENVELOPED VIRUSES only                                                      

2.4 Enzymes                                                                                                             

3. General Reproduction Cycles of Viruses

4. Types of Viruses

4.1 Bacteriophages                                                                             

4.1.1 T4 Phage – A Virulent Phage                                           

Reproductive Cycle – The LYTIC CYCLE                                                                      

4.1.2 Lambda phage – A Temperate Phage                                                                         

Reproductive Cycle – The LYSOGENIC CYCLE                                                             

Concept Check

4.2 Enveloped Animal Viruses                                                                                               

4.2.1 Influenza Virus                                                                                                                

          Reproductive Cycle for Influenza Virus                                                                       

4.2.2 Human Immunodeficiency Virus (HIV)                                                                       

          Reproductive Cycle for HIV                                                                                           

5. Mechanisms for Variation in Viral Genomes

5.1         Overview of Antigenic Shift and Antigenic Drift                                                

5.2          Mechanism of Antigenic Shift                                                                              

5.3          Mechanism of Antigenic Drift                                                                              

5.4          Effect of Antigenic Shift and Drift