RVHS 14. Organisation of Genomes - Viruses 9477

River Valley High School 2025 JC1 H2 Biology Lecture Topic 14: Organisation of Genomes – Viruses 1 River Valley High School 2025 JC1 H2 Biology Lecture Topic 14: Organisation of Genomes – Viruses Name: ( ) Class: 25J__ Date: References Title Author Biology (8th edition) Campbell and Reece Biological Science 1: Organisms, Energy & Environment (3rd edition) Taylor, Green and Stout Brock Biology of Microorganisms (12th edition) Madigan, Martinko, Dunlap and Clark Foundations in Microbiology (7th edition) Talaro Microbiology (4th edition) Baker, Griffiths, Nicklin H2 Biology Syllabus 9477 (2025) Candidates should be able to use the knowledge gained in the following section(s) in new situations or to solve related problems. Related Topics Content Organisation of Genomes - Prokaryotes Role of bacteriophage in bacterial transduction Infectious Diseases How viruses cause disease in humans Learning Outcomes 1A. Organelles and Cellular Structures 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. 2B. Organelles and Cellular Structures a. 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). b. Describe how the genomes of viruses are inherited through outlining the reproductive cycles of: i. bacteriophages that reproduce via lytic and lysogenic cycles, e.g. lambda phage; ii. enveloped viruses, e.g. influenza; and iii. retroviruses, e.g. HIV. c. Describe how variation in viral genomes arises, including antigenic shift and antigenic drift. Extension Topic A: Infectious Diseases g. Explain how viruses, including influenza and HIV, cause diseases in humans through the disruption of host tissue and functions (e.g. HIV and T helper cells, influenza and epithelial cells of the respiratory tract).

River Valley High School 2025 JC1 H2 Biology Lecture Topic 14: Organisation of Genomes – Viruses 2 Lecture Outline I. Characteristics of Viruses A. Are viruses alive? B. Viruses are obligate intracellular parasites C. Viruses exhibit host specificity II. Viral Structure III. Reproductive Cycles of Viruses A. General features of viral reproductive cycles B. Reproductive cycles of naked virus- Bacteriophage B1. Lytic and Lysogenic cycle of lambda phage C. Reproductive cycle of enveloped virus – Influenza D. Reproductive cycle of retrovirus – Human Immunodeficiency Virus E. Comparison of reproductive cycles of viruses IV. Variation in Viral Genomes A. Antigenic Drift B. Antigenic Shift V. Viral Infections A. How viral infections cause diseases B. Impact of Influenza infection C. Impact of HIV infection

River Valley High School 2025 JC1 H2 Biology Lecture Topic 14: Organisation of Genomes – Viruses 3 Websites URL Description http://bio-alive.com/animations/virology.htm List of virology animations https://highered.mheducation.com/sites/9834092339/stud ent_view0/chapter23/how_the_hiv_infection_cycle_works .html Animations on reproductive cycles of HIV *Note: you would need to use a laptop/desktop and download a chrome extension (e.g. “Flash Player for Chrome”) to view the tutorial. http://viralzone.expasy.org/all_by_species/254.html Baltimore classification of viruses https://www.researchgate.net/publication/8131916_Are_ Viruses_Alive Insights from Scientific American: Are Viruses Alive?

River Valley High School 2025 JC1 H2 Biology Lecture Topic 14: Organisation of Genomes – Viruses 4 I. CHARACTERISTICS OF VIRUSES Are viruses alive? Viruses are considered to exist at the border between chemistry and life, because they possess both living and non-living characteristics. Living characteristics: 1. Viruses can reproduce at a fast rate, but only upon infecting living host cells. 2. They possess a genome, and are capable of transmitting their genetic characteristics from one viral generation to the next. Viral genomes are also capable of evolving by natural selection. Non-living characteristics: 1. Viruses are acellular, since they lack key cellular components such as cytoplasm and cellular organelles. In their simplest forms, they comprise only genomic nucleic acid (DNA or RNA) surrounded by a protein coat. 2. They do not carry out metabolic processes ou tside a host cell, since they la ck essential cellular machinery, and are thus unable to grow and divide on their own. 3. While all cells contain double -stranded DNA genomes, viruses have either DNA or RNA genom es, which can in turn be single or double-stranded. 4. They are not capable of movement, because they lack the means to physically propel themselves B. Viruses are obligate intracellular parasites ⬧ A virus is a sub-microscopic infectious agent that cannot replicate independently of a host cell, the cell which is infected by the virus. ⬧ Viruses are therefore obligate intracellular parasites that must rely on entering a suitable living cell, i.e. infecting a host cell, to carry out their replication cycle and thus multiply. ⬧ Upon infecting a host cell, the virus hijack host cell machinery and exploits the energy resources, raw materials and metabolic machinery of the host cell. o The virus redirects host metabolic functions to support its own replication cycle via the assembly of new viral particles. Eventually, the new viral particles are released, and the process can repeat itself as the infection spreads. ⬧ Although viruses can only replicate after infecting a host cell, they have an extracellular form, known as the viral particle or virion1 that enables them to exist outside the host for long periods , and that facilitates their transmission from one host cell to another. o Viral particles can be passed from host to host either through direct contact (e.g. body fluids) or through a vector or carrier (e.g. dengue is transmitted by Aedes mosquito) 1 Virion is a term used for viral particle that is outside the host cell.

River Valley High School 2025 JC1 H2 Biology Lecture Topic 14: Organisation of Genomes – Viruses 5 C. Viruses exhibit host specificity Host specificity of viruses due to complementary binding between viral surface proteins and host cell surface receptors While viruses infect all types of organisms, from animals and plants to bacteria and archaea2, each type of virus infects only a limited variety of hosts. Thus viruses exhibit host specificity. Virus infects specific host cell by a ‘lock-and-key’ fit between viral surface proteins and specific receptor molecules on the host cell surface. 2 Archaea is one of the two prokaryotic domains, the other being Bacteria. The domain comprises unicellular organisms that are genetically distinct from bacteria and eukaryotes, and often found inhabiting in extreme environmental conditions. Checkpoint 1: Tobacco Mosaic Virus (TMV) has been isolated from virtually all commercial tobacco products. Why is TMV infection not an additional hazard for smokers?

River Valley High School 2025 JC1 H2 Biology Lecture Topic 14: Organisation of Genomes – Viruses 6 II. VIRAL STRUCTURE Representation of structure of a naked virus (left) and an enveloped virus (right) ⬧ Most viruses are smaller than prokaryotic cells, ranging in size from 0.01 – 0.3 µm. They are visible only under the electron microscope. ⬧ Their structures are diverse, varying widely in size, shape and chemical composition. ⬧ Nonetheless, all viruses contain a genome and capsid 1. Vira