Double Helical Structure Essay

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A DNA molecule consists of a double helical structure made up of two strands running in opposite directions and twisted around each other. The helical structure of a DNA molecule is similar to the structure a corkscrew or a spring. Running in opposite directions meant that the DNA strands are anti-parallel to each other where one strand has 3’ end at its terminal while the other strand has 5’ end at its terminal. 5’ and 3’ indicates the carbon numbers in the DNA’s deoxyribose sugar backbone. A 5’ end has a phosphate group and 3’ end has a hydroxyl group.

Starting off from its basics…
The basic units (monomers) of DNA are called nucleotides. Each nucleotide consists of:
• A five-carbon deoxyribose
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Each strand of the DNA has a sugar-phosphate backbone. The deoxyribose sugar and phosphate group are joined together by phosphodiester bonds. To hold the two strands together to form a DNA molecule, hydrogen bonds are present between two complementary bases on the different strands. Each nitrogenous base pairs with a complementary partner; Adenine pairs with Thymine with double hydrogen bonds; Guanine pairs with Cytosine with triple hydrogen bonds.

Factors affecting the double-helical structure of DNA
Besides having hydrogen bonds between the bases to hold the two DNA strands together, the backbone of the polynucleotides must be highly charged too. A strong repulsion between the two strands and will cause them fall apart if there is no salt in the surrounding medium. Thus counter-ions in the surroundings are essential for the double helical structure as they serve as shields for the charges on the sugar-phosphate backbone. These ions also provides attractive interactions with the fluctuating counter-ions around the backbone for fluctuating induced dipoles.

Under different conditions such as hydration, thermal fluctuations or applied force and/or twist, the DNA adopts several different helical

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