(a) (i) Watson and Crick's discovery of double helical structure was based on which two findings. Also mention the name of the scientists associated…

$\displaystyle \diamond$ Maurice Wilkins and Rosalind franklin, – X- ray diffraction studies of DNA.

$\displaystyle \diamond$ Erwin Chargaff ,– For a double stranded DNA the ratios between Adenine and Thymine and Guanine and Cytosine are constant and equal to one.

The salient features of double helix structure of DNA are as follows :

$\displaystyle \diamond$ It is made of two polynucleotide chains, in which backbone is constituted by sugar phosphate and the bases project inside.

$\displaystyle \diamond$ The two chains have antiparallel polarity.

$\displaystyle \diamond$ The bases in two stands are paired through hydrogen bonds forming base pairs(bp). Adenine form double hydrogen bond with thymine and Guanine form triple hydrogen bond with cytosine.

$\displaystyle \diamond$ The two chains are coiled in a right handed fashion.The pitch of helix is $\displaystyle 3.4$ nm and 10b.p in each turn. Distance between base pair in a helix is approximately $\displaystyle 0.34$ nm .

$\displaystyle \diamond$ The plane of one base pair stacks over the other in double helix.

(Any three points)

Template strand

$\displaystyle 3$' – TAC TGG CAT AAA AGA CAT CAC GGG CAT GAA GTC CGT AAT – $\displaystyle 5$'

m – RNA

$\displaystyle 5$' – AUG ACC GUA UUU UCU GUA GUG CCC GUA CUU CAG GCA UUA – $\displaystyle 3$'

In a bacterium

$\displaystyle 5$' – AUG ACC GUA UUU UCU GUA GUG CCC GUA CUU CAG GCA UUA – $\displaystyle 3$'

In humans

$\displaystyle 5$' – mGppp AUG ACC UUU UCU GUG CCC CUU CAG GCA UUA – poly A tail $\displaystyle 3$'

It will have $\displaystyle 10$ amino acids .