This type of bond is called a glycosidic bond. The phosphate group forms a bond with the deoxyribose sugar through an ester bond between one of its negatively charged oxygen groups and the 5' -OH of the sugar. Nucleotides join together through phosphodiester linkages between the 5' and 3' carbon atoms to form nucleic acids.
The 3' -OH of the sugar group forms a bond with one of the negatively charged oxygens of the phosphate group attached to the 5' carbon of another sugar. When many of these nucleotide subunits combine, the result is the large single-stranded polynucleotide or nucleic acid, DNA. If you look closely, you can see that the two sides of the nucleic acid strand shown above are different, resulting in polarity.
At one end of the large molecule, the carbon group is unbound and at the other end, the -OH is unbound. Deoxyadenosine-5'-monophosphate or deoxyadenylate dAMP. Deoxycytidine-5'-monophosphate or deoxycytidylate dCMP.
Deoxyguanosine-5'-monophosphate or deoxyguanylate dGMP. Base-pairing takes place between a purine and pyrimidine: namely, A pairs with T, and G pairs with C. In other words, adenine and thymine are complementary base pairs, and cytosine and guanine are also complementary base pairs. Adenine and thymine are connected by two hydrogen bonds, and cytosine and guanine are connected by three hydrogen bonds. The diameter of the DNA double helix is uniform throughout because a purine two rings always pairs with a pyrimidine one ring and their combined lengths are always equal.
Figure 9. There is a second nucleic acid in all cells called ribonucleic acid, or RNA. Each of the nucleotides in RNA is made up of a nitrogenous base, a five-carbon sugar, and a phosphate group. In the case of RNA, the five-carbon sugar is ribose, not deoxyribose.
RNA nucleotides contain the nitrogenous bases adenine, cytosine, and guanine. Molecular biologists have named several kinds of RNA on the basis of their function. For this reason, the DNA is protected and packaged in very specific ways. In addition, DNA molecules can be very long. Stretched end-to-end, the DNA molecules in a single human cell would come to a length of about 2 meters. Thus, the DNA for a cell must be packaged in a very ordered way to fit and function within a structure the cell that is not visible to the naked eye.
The chromosomes of prokaryotes are much simpler than those of eukaryotes in many of their features Figure 9. Most prokaryotes contain a single, circular chromosome that is found in an area in the cytoplasm called the nucleoid.
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