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Question: According to the original model of DNA, as proposed by Watson and Crick in 1953. DNA is a A. Righ...

According to the original model of DNA, as proposed by Watson and Crick in 1953. DNA is a
A. Right handed helix
B. Helix that makes a full turn every 70 nm
C. Helix where one turn of DNA contains 20 base pairs
D. Two stranded helix where each strand has some polarity

Explanation

Solution

DNA is a macromolecule, polymers of nucleotides, linear, spirally coiled in eukaryotes and circular in prokaryotes. It controls the structure and function of cells through transcription and translation. It was discovered by F. Miescher in 1868 in pus cells and was named nuclein.

Complete answer:
J. D. Watson and Francis H. C. Crick proposed a model of DNA structure as a double helix form. They inferred that in each DNA molecule there are two long and parallel nucleotide chains helically coiled around the same axis.
The right handed helices are held together by their bases which are paired together by covalent hydrogen bonds. There are ten base pairs per turn of the double helix. Two helices are coiled in such a way that they cannot be separated without unwinding.
The backbone of the helix is a chain of sugars and phosphates alternating with each other.
The two chains of a helix are of opposite polarity i.e. anti-parallel 3’-5’ and 5’-3’ in direction.
A large size purine comes opposite a small sized pyrimidine which generates uniform distance between the two strands of helix.
DNA has a 3D configuration dextrorotatory negative charged molecule where the 5' end of each chain bears phosphate radical and 3’end has sugar residue. Planes of adjacent base pairs are stacked over one another. The stacking along with hydrogen bonding confers stability to the helical structure.

Note: DNA is found in all living cells except mature mammalian RBC and sieve tubes. It is found in chromatin of nucleus in eukaryotes, nucleoid, and plasmid of prokaryotes (as circular strand) mitochondria, and plastids.