BIOC20 - LECTURE 5 EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED

BIOC20 - LECTURE 5 EXAM QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED What happens after viruses bind and internalize? Viruses must uncoat and be targeted to the right site. What mediates membrane fusion in viruses and how? Specific viral proteins (fusogens), which are type I transmembrane proteins. No ATP is needed, fusion occurs through metastable conformational changes. Where are fusion proteins made and assembled? Fusion proteins are made and assembled in the endoplasmic reticulum (ER) and undergo maturation. Fusion proteins are cleaved by cellular proteases. What reveals a fusion peptide in fusion proteins? Conformational changes reveal a fusion peptide, which is inserted into the target membrane. How do the membranes come together (host and viral)? The viral and host membranes fuse together to form a channel as the fusion proteins fold. What are class I fusion proteins and what are the two conformations? α-helical that form trimers. The two conformations are perpendicular to the envelope surface (pre-hairpin) and hairpin conformation after fusion. What are the characteristics of class II fusion proteins? Class II fusion proteins are β-sheets that form dimers and are parallel to the surface. What are the characteristics of class III fusion proteins? Class III fusion proteins are a combination of α-helices and β-sheets and consist of fusion and receptor binding subunits. What is the mechanism of penetration for non-enveloped viruses? Membrane lysis or pore formation. How can viruses penetrate the host membrane without rupture? Binding to the receptor causes a conformational change (loosen capsid). Hydrophobic proteins in capsids can create membrane channels. How do viruses get transported intracellularly? Take advantage of the cellular transport systems that cells normally use for moving vesicles and other molecules. Virions transported along microtubules with molecular motors: dynein & dynactin. Exception: Small viruses can freely diffuse. Why do DNA viruses use the nucleus as a replication site? What can viruses do in the nucleus? They can utilize the cellular machinery already present for transcription. Establish latency or integrate their genome into the host's genome. What is the disadvantage of using the nucleus as a replication site? Everything must pass through the nuclear membrane. How do viruses enter the nucleus?