In some viruses, DNA is synthesised by using RNA as template. Such a DNA is called :

Options

A. A-DNA
B. B-DNA
C. c DNA
D. r DNA

Answer

To solve the question, we need to identify the type of DNA synthesized from RNA in certain viruses. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the question
The question asks about a specific type of DNA that is synthesized using RNA as a template in some viruses.

**Hint:** Focus on the relationship between RNA and DNA in the context of viral replication.

### Step 2: Identify the process involved
In some viruses, particularly retroviruses, the process of synthesizing DNA from RNA is known as reverse transcription. This is a key concept in understanding how these viruses operate.

**Hint:** Remember that reverse transcription is the opposite of the typical transcription process where DNA is used to synthesize RNA.

### Step 3: Recognize the enzyme responsible
The enzyme that catalyzes this reverse transcription process is called reverse transcriptase. This enzyme is crucial for the synthesis of DNA from an RNA template.

**Hint:** Think about the role of enzymes in biological processes and how they facilitate reactions.

### Step 4: Define the type of DNA produced
The DNA synthesized from RNA through reverse transcription is referred to as complementary DNA, abbreviated as cDNA. This term is specifically used to denote DNA that is complementary to the RNA template.

**Hint:** Consider the meaning of "complementary" in the context of nucleic acids.

### Step 5: Analyze the options given
Now, let’s evaluate the options provided:
- A-DNA: This is a form of DNA but not specifically related to RNA templates.
- B-DNA: This is the most common form of DNA in cells, not related to RNA templates.
- C-DNA: This stands for complementary DNA, which is synthesized from RNA.
- R-DNA: This can refer to ribosomal DNA or recombinant DNA, neither of which fits the description.

**Hint:** Eliminate options that do not relate to the synthesis of DNA from RNA.

### Conclusion
Based on the analysis, the correct answer is **C-DNA** (complementary DNA).

**Final Answer:** C-DNA