Viruses

IB Biology

True or false?A virus can only reproduce inside a living cellViruses may stay in an inactive state for a long time inside a host cellViruses are larger than bacterial cellsViral DNA is coiled into chromosomesViruses can potentially be used to cure genetic disordersViruses cannot infect other viruses

Introduction to viruses

• Smallest living organisms (20nm-300nm)

• Obligate parasites

• Only reproduce in living cells

• Viruses transferred between cells as inert particles known as virions

Different Shapes

Helical Polyhedral Enveloped Bacteriophage

Functions of capsid and envelope

• Protecting the nucleic acid from enzymes and chemicals when virus is outside host cell

• Binding to the surface of the host cell

• Assisting in penetration of the host cell

Methods of entry into host cell• Direct translocation across the membrane

• Fusion of viral and cell membranes

• Uptake by phagocytosis/endocytosis

virusHost cell membrane

Retroviruses

• Have RNA not DNA

• Use reverse transcriptase to change:

single strand RNA double strand DNA

http://www.youtube.com/watch?v=FdjvDj5YRwE&feature=related

What is a cDNA library?

• complimentaryDNA (cDNA)

• cDNA created from mRNA using reverse transcriptase

• cDNA library : complete set of all the molecules contained within a cell or organism

Gene Therapy and Viruses