Retroviruses like HIV, the pathogen responsible for AIDS, incorporate an RNA template that is copied into DNA duringinfection. The reverse transcriptase enzyme that copies RNA into DNA is relatively nonselective and error-prone, leadingto a high mutation rate. Its lack of selectivity is exploited by the anti-HIV drug AZT (3′@azido@2′,3′@dideoxythymidine),which becomes phosphorylated and is incorporated by reverse transcriptase into DNA, where it acts as a chain terminator.Mammalian DNA polymerases are more selective, having a low affinity for AZT, so its toxicity is relatively low.(a) Draw the structures of AZT and natural deoxythymidine.(b) Draw the structure of AZT 5′@triphosphate, the derivative that inhibits reverse transcriptase.*2
Coding Strand of DNA
When pointing to DNA transcription, the coding strand is found to be the DNA strand whose base sequence is indistinguishable from the base sequence of the RNA transcript developed. It is this strand that comprises the codons, while the non-coding strand comprises the anti-codons.
Nucleotide
Both DNA and RNA are composed of organic molecules known as nucleotides. Hence, nucleotides are known as the basic building blocks of nucleic acids. These substances play a role in various processes such as cell signalling, enzyme reactions, metabolism, and so on.
Structure of Cytosine
Cytosine is among the five primary nitrogenous bases of which DNA and RNA and are being used in storage and transportation of genetic makeup within a cell. Adenine, guanine, thymine as well as uracil are the remaining four nucleobases.
Retroviruses like HIV, the pathogen responsible for AIDS, incorporate an RNA template that is copied into DNA during
infection. The reverse transcriptase enzyme that copies RNA into DNA is relatively nonselective and error-prone, leading
to a high mutation rate. Its lack of selectivity is exploited by the anti-HIV drug AZT (3′@azido@2′,3′@dideoxythymidine),
which becomes phosphorylated and is incorporated by reverse transcriptase into DNA, where it acts as a chain terminator.
Mammalian DNA polymerases are more selective, having a low affinity for AZT, so its toxicity is relatively low.
(a) Draw the structures of AZT and natural deoxythymidine.
(b) Draw the structure of AZT 5′@triphosphate, the derivative that inhibits reverse transcriptase.
*2
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