A2.3 Viruses

Question 1

A2.3.1 (HL) Structural features common to viruses - small size

Answer 1

Most are between 20-300 nanometres in diameter.

Must be smaller than their host cells to enter. Also small bc lack cytoplasm + other structural features.

Question 2

A2.3.1 (HL) Structural features common to viruses - fixed size

Answer 2

Viruses do not grow so they do not increase in size.

Question 3

A2.3.1 (HL) Structural features common to viruses - genetic material

Answer 3

All viruses have genes made of nucleic acid and they use the universal genetic code.

Question 4

A2.3.1 (HL) Structural features common to viruses - Protein capsid

Answer 4

Before viruses are released from their host cell, their genetic material is enclosed in a protein coat.

Question 5

A2.3.1 (HL) Structural features common to viruses - Cytoplasm and enzymes

Answer 5

Have no cytoplasm and contain no (or few) enzymes. Rely on the hosts metabolism.

The viral enzymes that are produced are required for genetic replication, infecting host cells or bursting host cells.

Question 6

A2.3.2 (HL) ​Diversity of Structure in Viruses - diversity of genetic material

Answer 6

DNA or RNA
Circular or linear
Double-stranded (ds) or single-stranded (ss)

Question 7

A2.3.2 (HL) ​Diversity of Structure in Viruses - diversity of genetic material replication in single-stranded RNA

Answer 7

Positive-sense RNA viruses: use their genes directly as mRNA.

Negative-sense: transcribe genes to make mRNA.

Retroviruses: make double-stranded DNA copies of RNA and then transcribe the negative-sense strand to produce mRNA.

Question 8

A2.3.2 (HL) ​Diversity of Structure in Viruses - Enveloped and non-enveloped viruses

Answer 8

In lysis (cell rupture), some viruses become covered in a membrane from the cell.