UNIT 3: Viruses

Question 1

Virology

Answer 1

The study of viruses

Question 2

Basic structure of viruses

Answer 2

All viruses are composed of an outer protein coat (capsid) surrounding a piece of DNA or RNA. They do not possess both types of nucleic acid.

Question 3

Rod-shaped viruses

Answer 3

• viruses that are rod-shaped have proteins packaged tightly into a helix e.g. tobacco mosaic virus

Question 4

Round shaped virus

Answer 4

Viruses that are round are composed of 20 identical proteins arranged into a Spherical protein coat e.g. rhinovirus which causes colds and flu

Question 5

Complex shaped viruses

Answer 5

Comprise a large group of viruses with shapes that vary widely. The most common shape is that of the bacteriophage -that infect bacterial cells.

Question 6

Obligate parasites

Answer 6

They can only replicate using a living cells

Question 7

Replication of viruses: attachment

Answer 7

The virus uses its external proteins to latch onto a target cell

Question 8

Replication of viruses: entry

Answer 8

Either the entire virus enters the cell or it injects its nucleic acid into the cell

Question 9

Replication of viruses: replication

Answer 9

The virus or the viral nucleic acid takes over the cells nucleus and protein synthesis system (ribosome). New viral proteins are synthesised and new copies of viral DNA/RNA are also synthesised

Question 10

Replication of viruses: assembly

Answer 10

The new DNA/RNA and viral proteins are assembled in their correct positions to make new viruses.

Question 11

Replication of viruses: release

Answer 11

The newly formed viral particles are released from the cell either by budding out through the cell membrane or by causing the cell to burst

Question 12

Beneficial effects of viruses

Answer 12

• viruses are regularly used in genetic engineering of various types of cells. They are used as vectors.
• it is hoped that bacteriophage viruses may in the future be used to treat serious bacterial infections in humans, eventually replacing antibiotics

Question 13

Harmful effects of viruses

Answer 13

• viruses can cause illness and disease: for example in humans viruses cause colds and influenza (rhinovirus), AIDS (HIV), hepatitis, poliomyelitis, measles and chicken pox. And in other organisms conditions such as foot and mouth disease in ruminants and various mosaic diseases in plants ( tobacco mosaic virus in the tobacco plant)

Question 14

Bacteriophage

Answer 14

A virus that infects bacteria