Viruses

Question 1

What are viruses?

Answer 1

They are acellular (not cells), nucleus acids surrounded by a protein.
They aren’t even alive

Question 2

Examples of viruses

Answer 2

• HIV which causes AIDS
  -Influenza which causes the flu
  -rhinoviruses which cause colds

Question 3

What do viruses do?

Answer 3

They invade and reproduce inside the cells of other organisms which are known as host cells.

Question 4

What is the basic structure of a virus?

Answer 4

• have no cell-surface membrane
• no cytoplasm
• no ribosomes
• have a protein coat called a capsid with attachment proteins sticking out from it
• attachment proteins allow the virus to cling onto a suitable host cell
• smaller than bacteria

Question 5

Viral replication

Answer 5

• they’re not alive so cannot undergo cell division.
  Instead, they inject their DNA or RNA into the host cell - this hijacked cell then uses its own ‘machinery’ (e.g. enzymes, ribosomes) to do the virus’s dirty work and replicate the viral particles.
  In order to inject their DNA or RNA, viruses first have to attach to the host cell surface.
  To do this they use their attachment proteins to bind to complementary receptor proteins on the cell-surface membrane of the host cells. Different viruses have different attachment proteins and therefore require different receptor proteins on host cells.
  As a result, some viruses can only infect one type of cell (e.g. some viruses can only infect one species of bacteria), while others can infect lots of different cells (e.g. influenza).