When one works with parvoviruses, one notices that some particles have a positive DNA whereas others...

When one works with parvoviruses, one notices that some particles have a positive DNA whereas others have a negative DNA. However all particles are equally infectious. What does it mean when DNA is positive or negative? You also observe that the following observations are perplexing:

a) dsDNA isolated from cells never denatures irreversibly, that is, no ssDNA molecular species are recovered;

b) DNA synthesis can proceed in-vitro in the absence of any primer. Explain the reason(s) for the anomalous behavior of this nucleic acid.

Expert Solution

DNA is positive (sense strand) means that the sequence of mRNA synthesized from DNA is similar to sense strand.

DNA is negative (anti-sense strand) means that the sequence of mRNA synthesized from DNA is complementary to this strand

minus strand is required for the synthesis of mRNA (minus strand is also called as template strand), RNA polymerase binds to minus strand and synthesize mRNA (sequence of mRNA is complementary to minus strand), which results in functional protein.

a) As soon as the virus enters the cells, the single strand DNA (either minus or plus strand) converts in to dsDNA by using host machinery. This double strand DNA now codes for mRNA for synthesis of virus proteins. So we will not observed single stranded viral DNA (ssDNA) when recovered from infected cells.

b) This ssDNA of virus has a palindromic sequences at both 5' and 3' ends. These sequences can fold back to form hairpin strand which serves as primer for DNA replication.

gladiator answered 2 years ago

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