YIJC [H2] CI2.10_Genetics of Viruses (N)(S) vetted (wo checkpoint answers)

2024 JC1 BIOLOGY LECTURE NOTES CORE IDEA 2: GENETICS AND INHERITANCE TOPIC 2.10: Genetics of Virus Learning Outcomes: You should be able to: Core Idea 1 (e) describe the structural components of viruses, including enveloped viruses and bacteriophages, and interpret drawings and photographs of them (f) discuss how viruses challenge the cell theory and concepts of what is considered living Core Idea 2 (d) [modifed] describe the structure and organisation of viral genomes (including DNA/RNA, single- /double-stranded, number of nucleotides, packing of DNA, linearity/circularity and presence/absence of introns) (e) describe how the genomes of viruses are inherited through outlining the reproductive cycles of: i. bacteriophages that reproduce via a lytic cycle only, including T4 phage ii. bacteriophages that reproduce via lytic and lysogenic cycles, including lambda phage iii. enveloped viruses, including influenza virus iv. retroviruses, including HIV (f) describe how variation in viral genomes arises, including antigenic shift and antigenic drift LECTURE OUTLINE 1 Nature of a virus particle ................................ ................................ ................................ ............ 2 2 Structure of a virus particle ................................ ................................ ................................ ........ 4 3 General features of viral reproductive cycle ……………………………………………………….. 10 4 Structure and Reproductive cycle of virulent bacteriophages e.g. T4 phage ............................ 11 5 Structure & Reproductive cycle of temperate bacteriophages e.g. Lambda phage................... 14 6 Structure & Reproductive cycle of enveloped viruses e.g. Influenza virus ................................ 18 7 Structure & Reproductive cycle of retroviruses e.g. HIV virus (HIV) ................................ ......... 22 8 Mechanisms for Variation in Viral Genomes ................................ ................................ ............ 28 H2

2 1 Nature of a virus particle 1.1 Are viruses alive?  Viruses are small infectious particles that can only replicate in their host cells.  These particles have a simple acellular organisation, consisting of viral genetic material (either DNA or RNA) enclosed in a protein coat called capsid (and a membranous envelope in some viruses).  Viruses are considered to exist at the border between chemistry and life, because they posses both living and non-living characteristics.  They display properties of living organisms only inside their host cells (intracellular phase) and are non-living outside their host cells (extracellular phase).  Living characteristics of viruses: o They are able to reproduce (though not independently). o They possess nucleic acids e.g. DNA or RNA that encode information for the reproduction of new viruses with the same characteristics as themsel