1. How many PFUs did you have on each plate? Plate A: Plate B: Plate C: Plate D:
ID: 272652 • Letter: 1
Question
1. How many PFUs did you have on each plate?
Plate A:
Plate B:
Plate C:
Plate D:
Plate E:
2. Assume you did a phage titration showing 6 plaques at 10-5 dilution and plated 0.3 mls from the dilutions. What is the number of phages/ml?
3. Name at least two phages of E. coli, give their physical characteristics and the chemical nature (e.g., dsDNA) of their genome.
4. What are possible reasons for not seeing any plaques? (Hint: “Maybe I did it wrong” is not the answer).
5. From the textbook chapter on viruses, indicate a way to count animal viruses.
Explanation / Answer
1. To calculate pfu one need to have background information on plating density /dilution of e.coli and knowledge as to what initial density for phage moi used. Without these information one cannot obtain an answer.
2. For 0.3 ml one could observe 6 plaques.
For plating 1 ml one should 6/0.3= 20 plaques.
Dilution factor =10^-5
Total number of pages= 20/10-5
=2×10-6 number of plaques.
3. Enterobacter phage T4 and lambda are the ones that ccan infect E.coli.
The T4 phage has a double stranded DNA enclosed in an icosahedral capsid along with a hollow tail so that it can pass the nucleic acid into the bacteria.
Another phage is lambda phage that has a head and a tail along with tail fibers. It has a Linear double stranded DNA with sticky ends called cos site. They have around 48,500 base pairs in their genome.
4. The growth of plaques is determined by several factors that include host strain, virus strain and conditions employed to do the infection. Either the phage is a lysogenic one and only upon entering lytic cycle can it show plaques.
5. Maximum of 3 question according to CHEGG. Hint: plaque assay, fluorescence based assay etc.
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