Nucleotides shapes

Transfer RNA (tRNA) Transfer RNAs are relatively small nucleic acids containing only about 70 nucleotides They get their name because they transfer ammo acids to the ribosome for incorporation into a polypeptide Although 20 ammo acids need to be transferred there are 50-60 tRNAs some of which transfer the same ammo acids Figure 28 11 shows the structure of phenylalanine tRNA (tRNA ) Like all tRNAs it IS composed of a single strand with a characteristic shape that results from the presence of paired bases m some regions and their absence m others... 

Base pair (bp) The four nucleotides in the DNA contain the bases adenine (A), guanine (G), cytosine (C), and thymine (T). Two bases (adenine and thymine or guanine and cytosine) are held together by weak bonds to form base pairs. The two strands of human DNA are held together in the shape of a double helix by those bonds between base pairs. For example, the complementary nucleic acid base sequence to G-T-A-C that forms a double-stranded structure with the matching bases is C-A-T-G. 

Molecular beacons are single-stranded hairpin-shaped nucleotide probes. In the presence of the target nucleotide sequence the molecular beacon unfolds, binds and fluoresces (Figure 6.13). 

DNA (short for 2-deoxyribonucleic acid) is the biological molecule that determines the shape and structure of all organisms. It is found mostly in the nuclei of cells. Each strand of DNA is a polymer that is composed of repeating units, called nucleotides. A single strand of DNA may have more than one million nucleotides. Each nucleotide consists of three parts a sugar, a phosphate group, and a base. 

A complete DNA molecule is a dimer, a molecule that consists of two similar units called monomers. Those units are extended strands of nucleotides joined to each other in a shape somewhat like that of a ladder. The two strands that make up a DNA molecule in turn are held together loosely by hydrogen bonds between adjacent nitrogen bases on opposite DNA strands. 

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