Q.Do biomolecules (DNA, protein) exhibit biological activity in anhydrous conditions?

No, biomolecules like DNA and proteins do not exhibit biological activity in anhydrous (completely dry) conditions. Biological activity depends on a specific three-dimensional structure, which in turn relies on weak interactions — hydrogen bonds, ionic bonds, van der Waals forces, and hydrophobic interactions. These weak forces require water to form and stabilise the correct conformation.

• Proteins lose their native folded structure (denature) when dehydrated, because water is essential for maintaining the hydrogen bonds that hold secondary and tertiary structures together. Without water, the active site collapses and catalytic or binding activity ceases.
• DNA also depends on water to stabilise its double helix via hydrogen bonding between base pairs and hydration of the sugar-phosphate backbone. In anhydrous conditions, the helix becomes disordered and cannot participate in replication, transcription, or other biological functions. …

Biological activity -- an enzyme catalysing a reaction, a DNA molecule being read or replicated, a protein binding its target -- is never just about having the right atoms present. It depends on the molecule holding a very specific three-dimensional shape, the native conformation. That shape is not held together by strong covalent bonds alone; it is stabilised by a network of weak interactions: hydrogen bonds, hydrophobic interactions, van der Waals forces and electrostatic (ionic) interactions. Every one of these weak forces is mediated by water.

Consider a protein first. Its polypeptide chain folds into a precise tertiary structure because hydrophobic side chains cluster away from water on the inside, while hydrogen bonds form both within the chain and with the surrounding water shell that coats the molecule's surface. Remove the water completely, and this entire scaffold collapses: hydrophobic residues have nothing to hide from, hydrogen-bond geometry is disrupted, and the protein loses its native fold. An enzyme's active site is a precise three-dimensional pocket built from exactly this kind of folding -- once the fold is gone, substrate binding and catalysis stop.

DNA tells the same story. The double helix is held together by hydrogen bonds between complementary base pairs and by base-stacking interactions, but the sugar-phosphate backbone also carries a shell of hydration -- ordered water molecules that stabilise the helix's precise geometry. Strip that hydration shell away entirely, and the helix distorts; the regular geometry that DNA polymerase, RNA polymerase and other DNA-binding proteins recognise is no longer presented correctly, so replication, transcription and other DNA-dependent processes cannot proceed normally. …

Method 2 -- separate the "structure" question from the "activity" question

It helps to treat this as two linked but distinct questions rather than one:

1. Can the covalent, primary structure survive drying? Yes -- the sequence of a protein's amino acids, and the sequence of bases in DNA, are held by strong covalent bonds (peptide bonds; phosphodiester bonds) that do not depend on water. Drying a sample does not chemically break these bonds.
2. Can the molecule's biologically active, folded/native shape survive drying? No -- that shape depends entirely on weak, non-covalent interactions (hydrogen bonds, hydrophobic interactions, van der Waals forces, electrostatic interactions), every one of which is mediated by water. Remove the water, and this shape is lost even though the covalent backbone is untouched. …