viruses Flashcards
what size are viruses?
Viruses are very small and unlike cells are measured in nm, not μm, varying in size between 10nm and 300nm
what do all viruses have?
•All viruses have a protein coat (capsid) that surrounds nucleic acid
•Depending on the virus concerned, the nucleic acid can be DNA or RNA
what are 2 types of viruses
•1. Bacteriophages
•2. HIV as a Retrovirus
what are bacteriophage
• Also known as phage viruses, have a relatively simple structure consisting of DNA core surrounded by a protein coat
•They are parasitic and their reproductive strategy involves them injecting the DNA into a host cell (the protein coat remains outside
• The DNA itself replicates to make copies that are then packaged
within the protein coats, forming new viruses
• In due course, the bacterial cell is destroyed as it ruptures and many new viruses are released to continue the cycle
Human immunodeficiency virus (HIV)
• Have an RNA core
• Outside the RNA core they have a typical protein coat, but in addition, have a lipid bilayer containing glycoprotein
• HIV viruses deliver the RNA into the host cell together with the enzyme reverse transcriptase
• The reverse transcriptase catalyses the synthesis of DNA from RNA
• The DNA then makes new viruses by synthesizing new protein coats and viral RNA
how does HIV cause AIDS
• In humans, HIV invades a type of lymphocytes called helper T-cells
• These T-cells are are very important in the immune system when
protecting against disease.
• As progressively more T-cells are destroyed, the immune system becomes critically compromised and the medical condition called AIDS can develop
why are viruses not true cells?
Viruses are not true cell; they no not have cytoplasm and the organelles associated with it.
• Crucially, viruses are inert unless they gain access to a living cell.
• In effect, they do not exhibit the characteristics normally associated with living organisms
