Type a paragraph about dna describing the following: • describe the structure of dna and what it is made of and how it is put together. use the following terms and underline them in your paragraphs. sugarnitrogen basecomplementary pairinghydrogen

1. DNA molecule is a double helix of 2 complementary polynucleotide strands;;

2. The two strands coil around each other to form a right-handed double helix;;

3. The strands are antiparallel, i.e. run in opposite directions (one strand runs in

the 5’ to 3’ direction while the complementary strand runs in the 3’ to 5’

direction);;

4. Each (polynucleotide) strand consists of very long chain of nucleotides, with

each nucleotide comprising of a deoxyribose sugar, a phosphate group and one

of the four nitrogenous bases - Adenine, Thymine, Cytosine or Guanine;;

5. Each strand contains a sugar-phosphate backbone – comprising of nucleotides

arranged in sequence, held together by phosphodiester bonds between C3 of

the (deoxyribose) sugar of one nucleotide and C5 of the (deoxyribose) sugar of

the adjacent nucleotide;;

6. The nitrogenous bases are arranged as side groups of the polynucleotide

strands (oriented toward the central axis);;

7. The width between the 2 sugar-phosphate backbones is constant at 2nm, this is

equal to the width of 1 base pair, i.e. 1 purine + 1 pyrimidine;;

8. One complete turn of the double helix measures 3.4nm in length and comprises

10 base pairs;;

9. The double helical nature of DNA results in the surface of the DNA molecule to

have major grooves and minor grooves;;

10. The nitrogenous bases of 1 strand pair with nitrogenous bases of the opposite

strand via hydrogen bonds. There are 2 hydrogen bonds between adenine and

thymine, and 3 hydrogen bonds between cytosine and guanine;;

11. Base pairing is complementary, i.e. adenine pairs with thymine, guanine pairs with cytosine. The base-pairing is specific and the 2 strands are said to be

complementary (i.e. no. of A = no. of T, no. of G = no. of C,);;

12. (extra pt) The DNA molecule is further stabilised by hydrophobic interactions between the stacked nitrogenous bases;;

13. The nucleosomes are connected by linker DNA and associates with H1 forming the nucleohistone complex;

14. Interactions between the H1 histones (histone tails of octamers and linker DNA) results in further coiling into a 30nm chromatin fibre;

15. The 30nm chromatin fibre form looped domains that are attached to a scaffold of non-histone proteins, giving rise to a 300nm fibre;

the correct answer is d