BIOL 1081 Lecture Notes - Lecture 24: Reverse Transcriptase, Macrophage, T Helper Cell
Ch. 27 LO
Viruses Reading: Sections 27.1-27.3 in textbook
1. Explain the basic structures, composition, and life cycle that viruses share.
• Structure-core of nucleic acid surrounded by protein, only DNA or RNA (linear/circular,
1x or 2x stranded), lacks cytoplasm, not a cell, capsid around nucleic acid core
• Composition
o Helical-rodlike threadlike appearance
o Icosahedron- 20 equilateral triangular facets, spider looking thing
• Life Cycle-
o Lytic Cycle
▪ Attachment-phage attaches to surface host cell wall
▪ Penetration- viral DNA enters host cell
▪ Synthesis-phage DNA replicates and phage proteins are made
▪ Maturation/Assembly-new phage articles are assembled
▪ Lysis- cell lyses, releasing the newly made phages
o Lysogenic Cycle-
▪ Attachment-phage attaches to surface host cell wall
▪ Penetration- viral DNA enters host cell
▪ Integration-Viral DNA becomes part of host DNA
▪ Cell Multiplication- Host replicates with viral DNA
▪ Assembly, Lysis, and Release- Cell enters back into lytic cycle
2. Distinguish between lytic and lysogenic bacteriophage, drawing a figure of each of the life
cycles.
• See paper
3. Describe the composition and source of viral envelopes, as well as their function in many
animal viruses.
• Viral envelopes covering protective protein capsids
• Envelopes are typically derived from portions of the host cell membranes, but include
some viral glycoproteins, which help them avoid host immune system
• Source- derived from host cell membranes
• Function-protection of protein, enables the virus to bind to host cells, inject poisonous
materials into the host
4. Draw and explain the life cycle of HIV.
• Attachment
o The gp120 glycoprotein on the surface of HIV attaches to CD4 and one of 2
coreceptors on the surface of a CD4+cell
• Entry into CD4+ cells
o Viral contents enter the cell by endocytosis
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