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Nucleotides
Nucleotides are composed of one phosphate group attached to the 5' carbon atom of one deoxyribose sugar an a nitrogenous base attached to the 1' carbon of the sugar. Long chains of nucleotides form a single strand of DNA. Covalent bonds link the 3' carbon of one nucleotide's sugar to the phosphate of another nucleotide. The Double Helix DNA is double stranded and helical in structure. Two complementary strands form a double helix, completing one turn ever 3.4 nm. This is approximately 10 base pairs for ever one turn. The two strands are antiparallel. This means one of the strands is "flipped" to allow the correct bonding and pattern to form. Looking at one section of a strand, the 5' end of a strand is that which ends with a phosphate attached to the 5' carbon atom of the deoxyribose. The 3' end has an exposed hydroxyl group at the 3' carbon atom of the deoxyribose. Therefore, the principle of antiparallel alignment says that if one strand runs 5' to 3', it's complementary strand runs 3' to 5' Nitrogenous Base Pairs DNA has nitrogenous bases adenine, thymine, cytosine, and guanine. The bases form pairs in a particular way based on their structure. Guanine always bonds with cytosine and adenine always bonds with thymine. This is called complementary base pairing. This lends to the structure of DNA in a couple of ways. Adenine and thymine form two hydrogen bonds. Cytosine and guanine form a stronger connection with three hydrogen bonds. Additionally, cytosine and thymine are pyrimidines, meaning they are made of one carbon ring while adenine and guanine are composed of two and are called purines. These properties cause the complementary base pairing that ensures DNA has a uniform width throughout its length, measuring 2nm across. |
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Rna vs. DNA
There are three main differences between the structures of RNA and DNA. RNA stands for ribonucleic acid. It is a single stranded nucleic acid instead of double stranded. Like DNA, it is composed of phosphate, a five carbon sugar and nitrogenous bases.
However, RNA's five carbon sugar is called ribose and has a hydroxyl group on its 2' C instead of a hydrogen. This sugar is less stable than deoxyribose. Also, RNA's nitrogenous bases are adenine, guanine, cytosine and uracil. Similar in structure to thymine, uracil replaces this base in RNA and is the complementary base pair of adenine.
There are three main differences between the structures of RNA and DNA. RNA stands for ribonucleic acid. It is a single stranded nucleic acid instead of double stranded. Like DNA, it is composed of phosphate, a five carbon sugar and nitrogenous bases.
However, RNA's five carbon sugar is called ribose and has a hydroxyl group on its 2' C instead of a hydrogen. This sugar is less stable than deoxyribose. Also, RNA's nitrogenous bases are adenine, guanine, cytosine and uracil. Similar in structure to thymine, uracil replaces this base in RNA and is the complementary base pair of adenine.