2016_H2_J2_Topic_L_Genetics_of_Viruses

NANYANG JUNIOR COLLEGE H2 Biology Genetics of Viruses J2/2016 1 GENETICS OF VIRUSES Learning Outcome Candidates should be able to: Core Topic 3 – Genetics of Viruses and Bacteria (a) Discuss whether viruses are living or non -living organisms and explain why viruses are obligate parasites. (b) Describe the structural components of viruses. (c) Describe the reproductive cycles of the following virus types: i. bacteriophages that reproduce via a lytic cycle, e.g. T4 phage; ii. bacteriophages that reproduce via a lysogenic cycle, e.g. lambda phage; iii. an enveloped virus, e.g. influenza; iv. retroviruses, e.g. HIV. (d) Explain how viral infections cause disease in animals, e.g. mammals, through the disruption of host tissue and functions (e.g. HIV and T helper cells [details of the immune system are not required], influenza and epithelial cells of the respiratory tract). Content Outline 1. Introduction 2. Definition of Life – Are Viruses Living or Non-living? 3. Structure of Viruses (a) Genome (b) Capsid (c) Envelope 4. Viral Reproductive Cycles (a) Reproductive cycle of bacteriophages, e.g. T4 phage, lambda phage (b) Reproductive cycle of enveloped viruses, e.g. influenza (c) Reproductive cycle of retroviruses, e.g. HIV 5. Viral Infections and Diseases 6. Course of HIV Infection in Humans References 1. Campbell N. A. & Reece J.B. (200 8). Biology. Chapter 1 9: Viruses. Eighth Edition. Pearson Education, Inc. 2. Brooker R.J. (2008). Biology. Chapter 18 : Genetics of Bacteria and Viruses . International Edition. The McGraw-Hill Companies.

NANYANG JUNIOR COLLEGE H2 Biology Genetics of Viruses J2/2016 2 1. Introduction All living organisms, either eukaryotes or prokaryotes, have nucleic acids which make up their genomes. Viruses possess nucleic acids but require the assistance of living cells to reproduce. As such, it becomes a debate as to whether viruses are living or non-living. Viruses are obligate parasites as they can reproduce only within a host cell as they lack organelles and metabolic enzymes necessary for protein synthesis and replication of the viral genome . Thus, isolated viruses , i.e. virions (infectious viral particles found outside a host cell ), are merely packaged sets of genes in transit from one host cell to another. In this topic, we will explore the structure of viruses, their reproductive cycles as well as the diseases caused by them. 2. Definition of Life – Are Viruses Living or Non-living? It has been an ongoing debate in the scientific world as to whether the virus is a living organism or a non-living particle. The consensus is that life is a characteristic of organisms that exhibit all or most of the following phenomena:  Organisation – Being structurally composed of one or more cells which are the basic units of life.  Metabolism – Consumption of energy by converting chemicals into cellular components (anabolism) and decomposing o