Question

The most common molecule used to spot on a DNA microarray is:

• A. cDNA
• B. Peptide
• C. mRNA
• D. Antibody

Hint:

While classical cDNA arrays are spotted mechanically, modern high-density oligonucleotide arrays (such as Affymetrix chips) are synthesized directly on the silicon substrate using photolithography.

Answer 1

The Correct Option is A

Step 1: Concept
A DNA microarray (or gene chip) is a solid surface (such as glass, silicon, or nylon) onto which microscopic spots of defined DNA sequences are attached at known coordinates.

Step 2: Identification of Spotted Molecules
The spotted target molecules (probes) must be stable, single-stranded, or denatured double-stranded DNA segments designed to hybridize with fluorescently labeled target nucleic acids in a sample. The most common molecules used for spotting are either chemically synthesized oligonucleotides or complementary DNA (cDNA) generated via reverse transcription of mRNA.

Step 3: Elimination
Free mRNA is too unstable (highly susceptible to ribonuclease degradation) to be spotted on a microarray. Peptides and antibodies are utilized in protein microarrays, not DNA microarrays.

Step 4: Conclusion
Hence, cDNA is the most common molecule spotted on a DNA microarray, matching option (A). Final Answer: (A)