Final answer:
The precursor molecule in nucleic acid synthesis is a nucleotide, which is composed of a sugar, phosphate group, and a nitrogenous base. tRNA fits the description of the nucleic acid purified from the mixture, and reverse transcriptase is the enzyme that HIV brings into a cell.
Step-by-step explanation:
The precursor molecule used in nucleic acid synthesis is a nucleotide. Nucleotides are the building blocks of nucleic acids, which include DNA and RNA. Each nucleotide is composed of a sugar, a phosphate group, and a nitrogenous base. During DNA synthesis, nucleotides are added to the growing DNA strand by the enzyme DNA polymerase, forming a phosphodiester linkage that makes the backbone of the DNA strand.
Considering the options provided:
- Nucleoside - a compound consisting of a sugar (ribose or deoxyribose) and a nitrogenous base; lacks the phosphate group.
- Nucleotide - a nucleoside with one or more phosphate groups. This is the correct answer.
- Ribosome - a cellular structure where proteins are synthesized, not involved in the initial synthesis of nucleic acids.
- Polypeptide - a polymer of amino acids, which forms proteins, not nucleic acids.
For the other related parts of the question:
- The tRNA is the molecule that is likely purified from a mixture which has small size, contains uracil, and most are covalently bound to amino acids. tRNA's main function is to bring amino acids to the ribosome during protein synthesis.
- Regarding HIV, it brings in an enzyme called reverse transcriptase, which is used to convert the viral RNA into DNA within the host cell.