Lecture 16

Question 1

Describe the main structural component of viruses and explain how they are produced

Answer 1

Structure
Size (20nm in diameter)
Contain nucleic acid which is packaged in a protective protein coat = capsid
Capsid is made up of repeating protein units (capsomeres)
Animal viruses, for example, influenza have a lipid envelope that surrounds the protein capsid
Lipid envelope derived from the plasma membrane of infected cells (protein and glycoproteins)
Reproduction
Infect specific types of host cell
The specificity of infection occurs during the attachment of the viruses to the host cell surface

Question 2

Contrast the reproduction of a virus with that of a living cell

Answer 2

The virus attaches itself to a specific host cell (the cell in which it will reproduce) the virus injects its genetic material into the host cell. the host cell uses the genetic material to make new viruses. the host cell splits open, releasing the viruses.
A cell divides, it makes a copy of all of its chromosomes, which are tightly coiled strands of DNA, the genetic material that holds the instructions for all life, and sends an identical copy to the new cell that is created.

Question 3

Describe and explain the lytic reproductive cycle of a bacteriophage

Answer 3

Attachment – the phage attaches itself to the surface of the host cell in order to inject its DNA into the cell
Penetration – the phage injects its DNA into the host cell by penetrating through the cell membrane
Transcription – the host cell’s DNA is degraded and the cell’s metabolism is directed to initiate phage biosynthesis
Biosynthesis – the phage DNA replicates inside the cell, synthesising new phage DNA and proteins
Maturation – the replicated material assembles into fully formed viral phages (each made up of a head, a tail and tail fibres)
Lysis – the newly formed phages are released from the infected cell (which is itself destroyed in the process) to seek out new host cells to infect

Question 4

Describe the retrovirus (HIV) cycle

Answer 4

After infecting a cell, a retrovirus uses an enzyme called reverse transcriptase to convert its RNA into DNA. The retrovirus then integrates its viral DNA into the DNA of the host cell, which allows the retrovirus to replicate. HIV, the virus that furthermore cause AIDS

Question 5

Explain the rapid rate of evolution in viruses and it’s consequences for human and animal health

Answer 5

Defence mechanisms i.e. the cell mediated immune system. Viral genomes change rapidly causing it to be particularly difficult for the defence mechanisms to fight the virus. An example of this is RNA viruses such as SARS , HIV, and influenza viruses, these have particularly high rate of mutation because RNA polymerase doesn’t have proof-reading and editing mechanism to correct mistakes