The reverse transcriptase activity of retroviruses like HIV is used to replicate their RNA genome in the host cell. This activity is not needed or present in DNA viruses which can use the host's  enzymes to replicate. The reverse transcriptase activity of telomerases is used to prevent telomere ends shortening after multiple replications in somatic cells. Telomeres are short sequences at the end of chromosomes that prevent deterioration of the chromosomes. Retrotransposones are elements that amplify repetitive sequences in the DNA of eukaryotes.

For biochemical purposes, it is important to have an understanding of the "Central Dogma" of molecular biology. DNA multiplies via replication, is turned into RNA via transcription, and finally to proteins via translation. Going back to DNA from RNA is known as reverse transcription, and is the correct answer. The term "reverse translation" can refer to an aspect of cloning, but does not naturally occur.

After transcription, mRNA is modified so that it can be preserved for a longer time in the cell. A nucleotide cap structure is attached to the 5' end of the mRNA and a poly A tail is attached to the 3' end of the mRNA in order to accomplish this goal.

We're given the type of enzyme contained within a virus, and we're asked to make a determination of the virus' genetic makeup.

To begin with, we're told that the enzyme is an RNA-dependent RNA polymerase. The name of the enzyme gives us insight into what it does. It requires RNA as a template to produce more RNA.

So if this enzyme can convert RNA into RNA, where does the original RNA come from? The answer is that it must come from the virus. This means that we must be dealing with single-stranded RNA.

Now, the question is to determine the sense of the RNA genome of the virus. That is to say, it can be minus or plus. A minus-sense RNA is one whose complementary sequence can be translated into protein. A plus-sense RNA is one that doesn't need any processing to be translated. Rather, plus-sense RNA can be translated right away. Since we know that the enzyme present is going to produce RNA from RNA, we can then reason that the viral genome is likely minus-sense. When the minus-sense RNA is enacted on by this enzyme, the result is a new strand of RNA that can be translated into protein to serve the needs of the virus.

The RNA transcript contains nucleotide bases at each position, which are complementary to the DNA. RNA is synthesized in the 5' to 3' direction from a DNA template strand with antiparallel direction (3' to 5').The coding DNA strand is identical to the RNA transcript with the exception that thymine is replaced with uracil in RNA. 

Eukaryotes have three types of RNA polymerase, I, II, and III. RNA polymerase II recognizes the promoter and binds to the promoter forming a preinitiation complex. The polymerase is composed of 10-12 subunits. Transcription factors also bind the promoter (the region of DNA upstream of the start or origin of transcription).In eukaryotes sigma protein factor is not required for transcription to occur.

Termination of transcription in prokaryotes (intrinsic termination) is mediated by special DNA secondary structures (stem and loop structures). Stem and loop structures have nucleotides that are complementary with the adjacent nucleotides. Along with a poly uracil sequence, these structures do not allow transcription to go further.In rho-dependent termination, rho binds to RNA until it reaches a RNA–DNA helical region, where it acts as a helicase and unwinds the complex. This in turn stops transcription. Sigma and TFIID are important in transcription in eukaryotes, not prokaryotes.

The correct answer is "six general transcription factors." RNA polymerase I is used to transcribe rRNAs, not mRNAs. The rho factor is used to initiate transcription in prokaryotes, not eukaryotes. Elongator is a factor used by eukaryotes to elongate transcripts and speed up transcription, but is not required to initiate transcription.

DNA replication occurs during the S phase of the cell cycle. Before DNA replication, the cell performs a check to ensure that there are no damages to the DNA molecules. One important molecule in this process is the cyclin-CDK complex. CDKs, or cyclin dependent kinases, are important kinases that facilitate the progression of cell through the cell cycle. Presence of CDK inhibitors will halt the progression of cell cycle and, subsequently, will halt DNA replication.

UV light is very damaging to DNA molecules. It changes the conformation of DNA molecules and prevents the activity of DNA replication enzymes; therefore, excessive UV light exposure will halt DNA replication.

Adenosine triphosphate, or ATP, is the main energy currency of the cell. It is used to power numerous energy consuming cellular processes. DNA replication requires lots of energy. Lack of energy, or ATP, will slow down DNA replication.

DNA methylation is an epigenetic process that involves the addition of a methyl group on DNA molecules. This makes the DNA molecule unavailable for and halts transcription. It does not stop DNA replication, however. Note that the methyl group added to the DNA here is different from the methyl cap added to RNA molecules during post-transcriptional processing.

The other epigenetic change that prevents transcription is the deacetylation of histones. Histones are proteins that facilitate the packaging and ordering of DNA molecules. Deacetylation of histones makes them more positive, strengthening the interaction between histones and negatively charged DNA molecules. This makes it harder for DNA molecules to open and be available for transcription.