6.Illustrate the double helix of DNA with details about base pairing, strand polarity, and physical dimensions.

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 6.Illustrate the double helix of DNA with details about base pairing, strand polarity, and physical dimensions.

answer:


polarity

Antiparallel - Direction and Polarity in DNA

DNA is Antiparallel

That DNA is antiparallel means that the two strands of DNA have opposite chemical polarity, or, stated another way, their sugar-phosphate backbones run in opposite directions. Direction in nucleic acids is specified by referring to the carbons of the ribose ring in the sugar-phosphate backbone of DNA. 5' specifies the the 5th carbon in the ribose ring, counting clockwise from the oxygen molecule, and 3' specifies the 3rd carbon in the ring. Direction of, and in reference to, DNA molecules is then specified relative to these carbons. For example, transcription, the act of transcribing DNA to RNA for eventual expression, always occurs in the 5' to 3' direction. Nucleic acid polymerization cannot occur in the opposite direction, 3' to 5', because of the difference in chemical properties between the 5' methyl group and the 3' ring-carbon with an attached hydroxyl group.


base pairing :

A base pair consists of two complementary DNA nucleotide bases that pair together to form a “rung of the DNA ladder.” DNA is made of two linked strands that wind around each other to resemble a twisted ladder — a shape known as a double helix. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G) [GWA-NeeN] or thymine (T). The two strands are held together by hydrogen bonds between pairs of bases: adenine pairs with thymine, and cytosine pairs with guanine.


How is DNA described as A three-dimensional spiral?
The structure of DNA is a double helix. In other words, it is a double stranded molecule that twists like a spiral staircase. The outsides of the molecule, the railings of the staircase, are made of deoxyribose sugars alternating with phosphates. This part of the molecule is sometimes called the "backbone".








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