Question

Why is HCl poured on the DNase test agar plates that you inoculated last period?

A. To cause intact DNA to precipitate, so the activity of DNase can be determined.
B. To kill the bacteria prior to observing them.
C. To stimulate the bacteria to produce DNase.
D. To cause degradation of DNA, so it easily can be taken up by bacteria.

Answer 1

Answer:The right option is A( to cause intact DNA to precipitate,so the activity of DNase can be determined.

Step-by-step explanation:

Deoxyribonuclease(DNase) test is used to determine the ability of an organism, usually of bacteria origin, to hydrolyse

DNA ( deoxyribonucleic acid). The organism uses the DNA present as a source of carbon and energy for growth. The DNase medium is grouped as a differential medium as it helps distinguish organisms able to produce DNase from non producing organisms. The medium is pale green in colour because of the DNA- methyl green complex. Methyl green( the indicator) is a cation which binds to the negatively charged DNA.

When an organism is inoculated onto the medium, if the organism that grows in the medium produces DNase,DNA will be broken down leading to the release of free methyl green cation in the medium. The green colour of medium fades and the colony is surrounded by a colourless zone.

But when the DNase agar is prepared without an indicator (methyl green), HCL is used for easy identification of the DNase activity.

Answer 2

A. To cause intact DNA to precipitate, so the activity of DNase can be determined.

Step-by-step explanation:

The presence of DNase is special feature for some species of bacteria and can be used for identifying them. During DNase test, diluted hydrochloric acid (HCl) can be poured onto the agar plates so that there will be a clear zone close to the bacteria colonies. Each nucleotides are soluble in diluted HCl. But DNA is not soluble in the diluted HCl, thereby making the DNA to precipitate in the rest of the plate.