Lecture 1: Characteristics of Viruses

Question 1

By the end of this Deck you should be able to:

• describe the structure of viruses
• describe the limitations of viruses
• Describe the differences between a number of viruses
• discuss were viruses fit in living organisms
• list some approaches to viral nomenclature

Answer 1

ye

Question 2

What is an Amoeba?
Escherichia coli?
Virion?
Viroid?
Prion?

Answer 2

Amoeba = eukaryote
Amoeba
A eukaryote
Escherichia coli 
A prokaryote
Virion
-Mature virus comprising all parts
Viroid
-Infectious circular RNA – plant pathogens
Prion
Infectious proteins

Question 3

What are the characteristics of a virus.
What is the structure of a virus?
7

Answer 3

• small infectious agents
• not a life form (non living)

Structure:

• nucleic acid genome (RNA or DNA)
• enclosed within a protein coat or Capsid
• can be further enclosed in lipoprotein membrane called an envelope
• contains simple enzymes

Question 4

Viral Nucleic Acid can only have 1 type and can be either?

10

Answer 4

RNA

• single stranded (ssRNA)
• double stranded (dsRNA)

DNA

• single stranded (ssDNA)
• double stranded (dsDNA)

All viral nucleic acid don’t contain all genes necessary for energy generation which means they are obligate intra cellular parasites

Question 5

What is a Viral Capsid ?

tell me some info on them

Answer 5

Its when there is protein coat covering the virus

• repeating proteins units
• can be symmetrical pattern
• has antigenic properties
• assis in attachment and entry
• protect nucleic acid from enzymes

Question 6

Viral envolope

Answer 6

• not found on all viruses
• lipis bilayer (made from membrane of host cell)
• if the virus is lacking an envelope its said to be a naked virus (more resistant to environment as envelope is easily damaged)

Question 7

How resilient are viruses outside host?

As in what environmental conditions can they survive in?

Answer 7

• most destroyed by heat 60 degrees for 30 mins
• some can last hrs at room temp
• some can last days at 4 degrees
• some stable in salt solutions
• generally stable at pH 5-9
• envelope can be destroyed by detergent
• chemically harder to kill than bacteria

Question 8

How are Viruses classified?

19

Answer 8

Families classed by nucleic acid DNA viruses and RNA viruses e.g. DNA viruses include

Question 9

How small are viruses in comparison to other things?

Answer 9

Smaller than bacteria but not a toxin. The agent is invisible by light microscopy and refractory to attempts to culture in the absence of plant cells

Question 10

What do viruses need living cells to replicate?

Answer 10

Viruses lack cellular organelles e.g. ribosomes therefore to produce viral proteins and replicate, they need to hijack the host cell synthetic machinery and force it to produce progeny viruses.
refer to table on slide 23 to see examples of viruses and their hosts

Question 11

Viruses are particles that are relatively simple

Answer 11

• Wendell Stanley nobel prize for crystallising tobacco mosaic virus (TMV)
• mehh refer to slide 25

Question 12

A virus genome is DNA or RNA explain.

26

Answer 12

• The genome of a virus is encoded in its nucleic acid
• virus genome can be composed of either RNA or DNA, but never both
• The nucleic acid genome may be single stranded or double stranded

Question 13

Give me the definition of a virus

Answer 13

“Viruses are entities whose genomes are elements of nucleic acid that replicate inside living cells using the cellular synthetic machinery and causing the synthesis of specialized elements that can transfer the viral genome to other cells.”

Question 14

Most specific for range of hosts

Answer 14

-plant viruses
-bacteria viruses
-animal viruses
can be specific for tissue
-some can cross species e.g. avian influenza virus