Virus Structure & Lytic vs Lysogenic Cycles

Question 1

What is a virus?

Answer 1

An infectious particle that injects its genetic material into a host

http://cdn4.sci-news.com/images/2013/02/image_905_1.jpg

Question 2

Name the three main structural components of a virus

Answer 2

Every virus is made up of…

• a nucleic acid (either DNA or RNA)
• a protein coat (capsid)
• sometimes an extra membranous envelope

http://img.sparknotes.com/figures/2/285caff64361a769a0850014b87c228c/structure.gif

Question 3

The capsid surrounding a virus can be in which three different shapes?

Answer 3

A rod, a polyhedral, and a separate more complex structure

Question 4

What is a bacteriophage and why are they significant in science?

Answer 4

Bacteriophages are viruses that infect bacteria, also just known as phages. These are significant because they led to scientific discoveries such as the lytic and lysogenic cycles, the way in which double stranded DNA viruses can replicate.

http://textbookofbacteriology.net/penetration.jpg

Question 5

Which cyle results in the death of the host cell?

Answer 5

The Lytic Cycle

The photo below depicts the cell lysing and releasing its phages

http://bio1151.nicerweb.com/Locked/media/ch19/19_01T4PhageEColi-L.jpg

Question 6

Describe the steps of the lytic cycle

Answer 6

After the phage has injected its DNA into the bacteria…

1. the phage begins to self-assemble and form multiple phage heads, tails and tail fibers
2. An enzyme is then released to puncture the cells wall and allow water to enter
3. The water causes the cell to lyse and release all its infectious viral phages
   http: //bio1151.nicerweb.com/Locked/media/ch19/19_05T4LyticCycle_5-L.jpg

the video below describes the lytic cycle:

https://www.youtube.com/watch?v=3DP-MAhr0YY

Question 7

What is a virulent phage?

Answer 7

A virus that only replicates using the lytic cycle

Question 8

What type of defense does bacteria orchestrate in order to prevent the lytic cycle from occuring?

Answer 8

The bacteria will send restriction enzymes to cut up the viruses DNA that is recognized as foreign to the cell

Question 9

Which cycle allows the phages to replicate but does not destroy them?

Answer 9

The Lysogenic Cycle

Question 10

What are temperate phages?

Answer 10

Phages that use both the lytic and lysogenic cycle

Question 11

Describe the steps of the lysogenic cycle

Answer 11

After the phage has injected its genetic material…

1. the phage circularizes and enters the lytic or lysogenic cycle
2. If it enters the lysogenic cycle, the phage becomes a prophage by binding to a bacterial chromosome
3. When the bacteria replicates and forms new daughter cells, the prophage is replicated as well and is soon passed on to many new bacteria cells

Here is a simple video for understanding the lysogenic cycle:

https: //www.youtube.com/watch?v=YJJv-tDvHy8
http: //bio1151.nicerweb.com/Locked/media/ch19/19_06LambdaLyticLysoCycle-L.jpg

Question 12

What are viruses unable to perform without injecting a host cell first?

Answer 12

Replication and metabolization.