DNA Synthesis from RNA Template in Viruses

In typical biological systems, genetic information flows from DNA to RNA and then to protein. This is often called the central dogma of molecular biology. However, some viruses, particularly retroviruses like HIV, have an enzyme that reverses part of this flow.

Process of DNA Synthesis Using RNA as Template

These viruses have their genetic material stored as RNA. Once inside a host cell, they use a special enzyme called reverse transcriptase. This enzyme reads the viral RNA sequence and synthesizes a complementary strand of DNA.

• The viral RNA serves as a template.
• Reverse transcriptase enzyme facilitates the synthesis.
• A single strand of DNA is created first, complementary to the viral RNA.
• Then, a second DNA strand is synthesized, making it a double-stranded DNA molecule.

This newly synthesized double-stranded DNA can then integrate into the host cell's genome.

Naming the DNA Synthesized from RNA Template

The DNA molecule produced using RNA as a template through reverse transcription is commonly referred to as complementary DNA, abbreviated as cDNA. This name reflects its nature of being complementary to the RNA template.

Based on the options provided, the DNA synthesized by using RNA as a template is referred to as C-DNA.

Other Forms of DNA Mentioned in Options

The options also mention A-DNA and B-DNA. These terms typically refer to different structural forms that double-stranded DNA can adopt under various conditions, not specifically how the DNA was synthesized.

• B-DNA: This is the most common form of DNA found in biological systems under physiological conditions. It has a right-handed helix.
• A-DNA: This form is seen under dehydrating conditions and in DNA-RNA hybrids. It is also a right-handed helix but is wider and shorter than B-DNA.
• C-DNA: While less common than A-DNA and B-DNA, C-DNA is also described as a right-handed helical form of DNA found under specific low humidity conditions and in the presence of certain ions. However, in the context of synthesis from an RNA template as described in the question, the term typically relates to complementary DNA (cDNA). Based on the provided options and question structure, C-DNA is given as the name for DNA synthesized from an RNA template.

Therefore, according to the options provided, the DNA synthesized by using RNA as template is called C-DNA.