Viruses

Question 1

What are viruses

Answer 1

Acellular organisms that cannot survive without a host

Question 2

Why do viruses need a host

Answer 2

They have no metabolic abilities of their own. Therefor cannot reproduce without help from host cells

Question 3

What do viruses infect

Answer 3

All types of cells - obligate intracellular parasites

Question 4

What are viruses composed of

Answer 4

Genetic material - DNA or RNA
Capsid - Surrounds and protects genetic material
In some cases envelope of lipids - surround capsid when outside cell

Question 5

Describe what capsids are

Answer 5

Multiple units of building blocks (capsomers) arranged in precise and repetitive pattern

Question 6

What are the 3 ways capsids can be arranged (symmetry)

Answer 6

Helical - rod shaped. Same repeat slightly offset to form spiral
Icosahedral - Triangular faces (20). Stable and strong
Complex - Helical tail and icosahedral tail

Question 7

What are the 3 arrangements of viral genome

Answer 7

Linear - Poxvirus
Circular - Hep B
Segmented - Influenza virus

Question 8

What are the possible forms of virus genomes

Answer 8

Single or double stranded RNA or DNA

Question 9

What are bacteriophages

Answer 9

Viruses that infect and replicate in bacteria

Question 10

Describe the stages of lytic cycle

Answer 10

1 - Attachment - Recognise receptor on cell surface
2 - Entry - of phage DNA and degradation of host DNA
3 - Synthesis of viral genomes and proteins
4 - Self assembly of virus
5 - Release - Virus escapes bacteria (bursts)

Question 11

How does the virus get out of the bacteria when formed

Answer 11

Produces T4-lysosome which breaks down peptidoglycan bonds (hold together bacteria wall)

Question 12

Describe lysogenic cycle

Answer 12

Viral DNA incorporated into hosts. Host continues to replicate, virus DNA as well.

Question 13

Can lysogenic cycle turn into lytic

Answer 13

Yes. Sometimes randomly virus DNA can separate from bacteria’s and begin replicating itself

Question 14

Why is HIV/AIDS so dangerous

Answer 14

It affects the CD4 cells of our immune system leaving us open to attacks from other bacteria and viruses

Question 15

Describe HIV virus composition

Answer 15

RNA enveloped virus - surrounded by glycoprotein

Question 16

Describe how HIV virus replicates in host cells

Answer 16

HIV membrane fuses with host to enter.
Breaks down capsid and releases RNA.
Uses host to synthesise complimentary DNA strand (Hybrid - reverse transcription)
Then synthesises another (ds)DNA strand and is incorporated into host DNA (Provirus)
This produces mRNA coded to produce virus proteins.
Newly made virus then fuses with membrane to release out of cell