Question

describe the structure of DNA molecule?​

Answer 1

Answer:

double helix structure

Explanation:

made of 2 polynucleotide chains

3 components are present ,they are

sugar base

nitrogenous base

phosphate group

Answer 2

Answer:

• The β-DNA molecule exists as a double helix. It has two unbranched polynucleotide strands. Each  polynucleotide strand/chain consists of a sequence of nucleotides linked together by phosphodiester bonds. The polynucleotide strands are antiparallel, i.e., run in the opposite direction.

• The two strands are not coiled upon each other but the double strand is coiled upon itself around a  common axis like spiral staircase with base pairs forming steps while the backbones of the two strands  form railings. The backbone is formed of sugar and phosphate.

• The nitrogen bases are projected more or less perpendicular to the sugar phosphate backbone but face  inside.

• The base-pairing is specific. Adenine is always paired with thymine and guanine is always paired with  cytosine. Thus, all base-pairs consist of one purine and one pyrimidine. Once the sequences of bases  in one strand of a DNA double helix is known, the sequence of bases in the other strand is also known  because of the specific base pairing. The two strands of a DNA double helix are thus said to be  complementary (not identical). This is known as complementary base pairing.

• The two polynucleotide strands are held together in their helical structure by hydrogen bonding between  bases in opposing strands. Adenine and thymine form two hydrogen bonds. Guanine and cytosine form  three hydrogen bond.

• One end of the strand is called 5′ end where the fifth carbon of the pentose sugar is free and the other  end is called 3′ end where the third carbon of pentose sugar is free.

• At each base pair the strand turns 36°. One full turn of the helical strand (360°) would involve ten base  pairs i.e., one turn of 360° of the helical strand has about 10 nucleotide on each strand of DNA. The  base-pairs in DNA are stacked 3.4 Å apart. Thus pitch of the DNA is 34 Å as ten base pairs occupy a  distance of about 34 Å.