Question

1) In most laboratory applications, for plate counts to be considered valid, they must have between 30 and 300 colony forming units on them. To achieve this, scientists must dilute the sample prior to plating it. If a culture of bacteria is experiencing exponential growth has 8,449 cells per mL, and an instantaneous growth rate constant of 0.5 hours-1, after 2 hours, what is the total dilution that needs to be performed to yield 71 colony forming units on an agar plate?

2)  A culture of bacteria contains 10⁹ cells per mL. In order to inoculate a flask with 100 mL of media so the initial culture will have 8,900 bacteria per mL, how many mL of culture should be transfered?

3) Group II viruses violate the Central Dogma.

Determine whether each of the following are True or False

a) Group II Viruses still use a DNA genome as a template for anti-sense DNA, which is then used as a template for RNA, which is then translated to proteins. This is still DNA -> RNA -> Protein.

b) Group II Viruses use an RNA genome as a template for for proteins.

c) Group II Viruses use a DNA genome as a template for DNA, which is then transcribed to mRNA. The Central Dogma is DNA -> RNA -> Protein. Group II viruses use a DNA -> DNA -> RNA -> Protein pathway.

d) Group II Viruses use an RNA genome to synthesize DNA, which is then used to synthesize mRNA, which is then used to synthesize proteins. This is still DNA -> RNA -> Protein.

Answer 1

1)

First let us find the bacterial amount after 2 hours

log (N₂/N₁) = k (t₂-t₁) / 2.303

= 0.5(2)/2.303 = 0.4342;

log (N₂/N₁)= 0.4342; N₂/N₁ = 2.7171, N₂= 2.7171 * N₁ = 22962.62

Now the dilution

22962.62 cfu * X ml = 71* 1 ml; x= 3 microlitres ; this means we take 3 microlitres of the sample and make the volume to 1 ml and then plate this on agar. So you the dilution factor is 1000/3= 330.

2)

10⁹ * X = 8900 * 100; X= 0.000890000= 0.8 microlitres

3) Answer is c) Sense strand (+) is used to derive - or anitsense DNA, but sense + strand is used to carry out mRNA synthesis