What are address blocks and how do they support random access in DNA storage?

• A. They stabilize data by cross-linking sequences.
• B. They encode parity information for error correction.
• C. They are unique sequences that identify data blocks and enable selective amplification and retrieval of specific blocks.
• D. They mark the end of data segments to prevent overrun.

Answer: (C)

In DNA storage, the main idea is to be able to pick out specific chunks of data from a giant pool of DNA molecules. Address blocks serve as unique identifiers for each data block. They are designed as distinctive sequences that sit with the data, acting like an address label and priming sites for amplification.

Because these address blocks are unique, you can design primers that specifically bind to one address and not to others. When you perform a targeted amplification (PCR) using the matching primers, only the data blocks with that address are amplified and recovered. This selective amplification lets you retrieve a single block—or a small set of blocks—without sequencing the entire pool, which is what enables random access.

Address blocks must be carefully designed to be orthogonal to each other and to avoid cross-reactivity, so retrieval remains precise. They aren’t primarily about stabilizing data with cross-links, nor about adding parity for error correction, and they don’t merely mark ends of segments. Those concepts refer to different aspects of the storage system; the address blocks specifically provide the identifiers that make selective, random retrieval possible.