1. Biotechnology Part 1 Genetics of Viruses
AP Biology
Biotechnology Part 1
Genetics of Viruses

2. What type of genetic material do viruses have?
Either a double of genetic material (DNA) or a single strand of genetic material (RNA)
How are viruses classified?
According to whether their genetic material is DNA or RNA
How much genetic material do viruses have?
A very small amount
Anywhere from 4 to 500 genes total

3. What is a capsid?
A protein coat around a virus
What is the purpose of the capsid?
It protects the DNA or RNA strands inside
It allows the virus to attach to a host cell

4. What makes up the capsid?
Protein units
What are these protein units called?
Capsomeres (or capsid units)

5. What is the viral envelope?
A sort of “cloak” that allows the virus to mimic a normal cell
It is like a Trojan horse, because the danger is inside
It is made from a part of the plasma membrane from the previous host cell

6. Where does the viral envelope of HIV originate?
It comes from the helper-T white blood cells that HIV invades
HIV
White blood cell

7. What are bacteriophages?
Viruses that attack bacteria
They are the largest and most complex viruses

8. Why is it impossible to kill viruses?
They are not living organisms
How can viruses be controlled?
They can be denatured using chemicals, heat, etc.
Anti-viral products, such hand soaps, sanitizers, kleenix, etc. may contain some of these chemicals

9. Even though viruses are not living, they can still….
Reproduce
What is essential in order for a virus to reproduce?
A living cell
What is an obligate Intracellular Parasite?
Something that uses the resources of another organism, and must be inside the cell to do so
What does the virus need from the host cell?
Its ribosomes and enzymes
Why does the virus need these?
To make new DNA or RNA

10. What is meant by the host range?
The different organisms that a virus is capable of attacking
How is this determined?
By whether the glycoproteins and glycolipids on the cell membrane of the host cell can be recognized by the virus (cell signaling)

11. What are restriction enzymes?
Enzymes in a bacteria that create a primitive defense system against the virus
They cut up the virus genome
This inactivates the genes and they cannot be transcribed

12. Why is the term “restriction” attached to these enzymes?
They can only cut at certain nucleotide sequences (therefore, they are restricted as to where they can cut)

13. What is the lytic cycle of a virus?
The part of the virus cycle that destroys the host cell
It will lysis the host cell (burst it open)
This cycle is described as virulent

14. What is the lysogenic cycle of the virus?
The virus cycle that permanently incorporates the virus DNA into the DNA of the host cell
This does not immediately kill the host cell
Every time the host cell reproduces, it reproduces the virus DNA at the same time

15. What could cause the lysogenic cycle of a virus to go into the lytic cycle?
When something aggravates the virus
It will then pull its DNA out of the host cell DNA, reproduce rapidly and burst out of the cell by lysis

16. What is a prophage or provirus?
Viral DNA that has been inserted into the bacteria DNA
The virus is in the lysogenic cycle at this stage
Herpes and HPV are examples
When they get aggravated, they will go into the lytic cycle, blisters will form, and the host cell is killed

17. What kind of aggravation causes a virus to go into the lytic cycle?
Stress, fever, sunburn, etc.
Fever blisters (cold sores) are caused by Type I Herpes, and usually occur after a fever, sunburn, or some other type of stress

18. What are retroviruses?
Viruses that use reverse transcriptase to turn RNA back into DNA
Retro means reverse or back
Transcription is being done backwards
HIV and the common cold are both retroviruses

19. What is gene therapy?
Genes for certain proteins or enzymes are inserted into virus capsids
These viruses are injected into a person that has a genetic disease in which they are missing those proteins and/or enzymes
Hopefully, the virus DNA containing the code for the missing protein will be taken into the DNA of the affected person’s cells

20. Virus “size”

21. Viral Structure

22. Glycoprotein Viral envelope Capsid RNA (two identical strands) Reverse.
Glycoprotein
Viral envelope
Capsid
RNA
(two identical
strands)
Reverse
transcriptase

23. How the envelope was acquired.

24. Bacteriophage

25. Viral Reproduction

26. Lytic Viral Life cycle Attachment Entry of phage DNA
and degradation of
host DNA
Phage assembly
Release
Head
Tails
Tail fibers
Assembly
Synthesis of viral
genomes and proteins

27. Lysogenic Viral Life Cycle
Phage
DNA
The phage attaches to a
host cell and injects its DNA.
Daughter cell
with prophage
Many cell divisions
produce a large
population of
bacteria infected with
the prophage.
Phage DNA
circularizes
Phage
Bacterial
chromosome
Occasionally, a prophage
exits the bacterial chromosome,
initiating a lytic cycle.
Lytic cycle
Lysogenic cycle
Certain factors
determine whether
The bacterium reproduces
normally, copying the prophage
and transmitting it to daughter cells.
The cell lyses, releasing phages.
Lytic cycle
is induced or
Lysogenic cycle
is entered
Prophage
New phage DNA and proteins are
synthesized and assembled into phages.
Phage DNA integrates into the
bacterial chromosomes, becoming a
prophage.