Chapter 13

Virus VS. Bacteria


Chemical and physical composition of an enveloped virus

-envelpe is made of fat, protein, and carbohydrates
- its derived from cell membrane of host cell
- it covers the capsid of the virus
- envelpe protects the virus from phagocytes
-some have spikes made of carbohydrate-protein complexes on the surface of t

Chemical and physical composition of a nonenveloped virus

- the capsid protects the nucleic acid from nuclease and enzymes and helps attach the virus to the host cell

Why are viruses sometimes referred to as being "semiliving"?

- only have some of the characteristics of life
- no metabolism
- no ribosomes
- no plasma membrane
- nucleic acids are not always active
- when viruses are outside of the host cell, they are inert and nucleic acids are not active
- when viruses are insid

one argument for and against the classification of viruses as living organisms

- For: They can be classified as living beings because they contain either DNA or RNA. The DNA/RNA are components of all living organisms and since virus having a component present in the living organisms can be called as a living thing.
- Against: On the

Viral Species

- group of viruses sharing the same genetic inofrmation and cological niche (host range)
- Common names are used for species.
- Subspecies are designated by a number.
- Family: Filoviridae
- Genus: Ebolavirus
- common name: Ebola

How are bacteriophages cultured?

- can be growin eith in suspensions of bacteria in liqud media or in bacterial cultures on solid media.
1. Solid media = plaque method
- sample of bacteriophage mixed with host bacteria and melted agar
- agar then poured into petri plare that has hardened

How are animal viruses cultured?

1. living animals:
- mice, rabbits, adn pigs
- animal is inoculated with the specimen and then observed for signes of disease or killed to examine the infected tissues
2. Embryonated eggs;
- holes drilled in the shel, viral suspension injected into the fl

Lytic cycle

- Phage attaches by tail fibers to host cell.
2. Penetration:
- Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into the bacterium.
3. Biosynthesis:
- Production of phage DNA and proteins. Viral

Lysogenic cycle

- some viruses do not cause lysis and death of the host cell when they multiply (lysogenic cycle)
- Phage attaches by tail fibers to host cell.
2. the originally linear phage DNA forms a circle
3. phage DNA attaches to host chro

How animal viruses multiply

- attachment site are protein and glycoproteins of the plasma membrane
- attachment sites distributed of the surface of the virus
- in enveloped virus, spikes are are the attachment sites
2. PENETRATION (entry): into host cell (2 ways)
- Re


- gene that has potential to cause cancer
- oncogenes can be activated to abnormal functioning by a variety of agents, including high energy radiation and viruses

Latent viral infection

- viruses that enter hose cell and remain dormant or replicate slowly with little damage to host cell
-may activate later if theres some stimulation
ex: cold sore, lukemia, shingles


-not cells
-neither procaryotic or eucatyoric
have either DNA or RNA NOT both
- every virus has a capsid around the nucleic acid
- multiply inside living host cell

obligatory intracellular parasites

-can reproduce ONLY inside living host cells
- won't grow on artifical media
- DO exist outside of the living host cell


-protein coat around the nucleic acid of a virus
- protects the genome
- gives shape to the virus
- composed of protein subunits called capsomeres
- some viruses have capsid covered by an envelope


-protein subunits that make up the capsid of a virus
- sometimes the protein is of single type and sometimes many types of protein are present
- arrangment is characteristic of a particular type of virus


- viruses that infect bacteria
- easiest virus to grow
-replicated in 20-40 minutes
-50-200 phages emerge

host range

- spectrum of host cells the virus can infect
- most viruses are able to infect specific types of cells of only one host species`

reverse transciptase

-use of viral RNA to synthesize DNA in the host cell
- this enzyme also degrades the original RNA
- the viral DNA id integrated into a host cell chromosome as provirus which never comes out of chromosome

oncogenic viruses

viruses capable of inducing tumors in animals
- 10% of cancers are knows to be virus-induces
- their genetic material integrates into the host cells DNA and replicated along with the host cells chromosome