Three important features might be these:-

(i) DNA is a long double  chain or duplex 'molecule' formed of millions of deoxyribonucleotides.

(ii) Length of DNA is characteristic of organism and its chromosomes.

(iii.a) DNA duplex has a diameter of 20Å

(iii.b) The duplex is coiled plectonemically in a right handed manner just as a rope stair is twisted to form a spiral.

(iii.c) This coiling produce alternate major (length 22Å) and a minor (length 12Å) grooves.

(iii.d) Each turn of spiral has a distance of 34Å.

(iii.e) This length contain 10 deoxyribonucleotides in each chain so that the average distance between adjacent deoxyribonucleotides is 3.4Å.

(iv.a) Four types of deoxyribonucleotides occur in DNA - dAMP (deoxyadenosine monophosphate), dGMP (deoxyguanosine monophosphate), dCMP (deoxycytidine monophosphate), dTMP (deoxythymidine monophosphate).

(iv.b) Each deoxyribonucleotide is further formed of three components - deoxyribose sugar (C₅H₁₀O₄), phosphoric acid and nitrogen base.

(iv.c) Two of four nitrogen bases are 9-membered double ring purines, adenine (A) and guanine (G). The remaining two are 6-membered single ring pyrimidines, cytosine (C) and thymine (T).

Hope this information helps...!
The hydrophobic effect. While the edges of the base pairs can make hydrogen bond contacts, the planar surfaces are relatively hydrophobic. Therefore, water is less ordered with the bases outside the helix (no base-paired) than when they are inside (base-paired). The hydrophobic effect that produces this arrangement is calledbase stacking.

2. The two strands are antiparallel.

That is one strand goes in the 3' to 5' direction, while its complementary strand goes in the opposite direction. This is shown in Figure 2.14, above.

3. The helix has three distinct forms:

Properties of DNA helices A Form B Form Z Form RNA-DNA Hybrid Direction of helix rotation rightright left right Residues per turn 11  1012 11Rotation per residue 33 deg. 36 deg. –30 deg. 33 deg. Rise  0.255 nm0.34 nm 0.37 nm 0.255 nm Pitch  2.8 nm3.4 nm 4.5 nm 2.8 nm 

A- form DNA occurs when the amount of water in the surrounding medium is about 75%. The B- form occurs at much higher moisture content, 92%. Z-DNA, or left-handed DNA occurs in regioins of high GC content. Notice that anRNA/DNA hybrid has the same structural parameters as A form DNA.

Here's a side-by-side comparison of A-form and B-form DNA, using wire-frame models: