Nucleic acids

Nucleic acids - Figure 8 shows how two strands of...

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Nucleic acids The genetic information of a cell is stored in molecules of  deoxyribonucleic acid (DNA).  The DNA,  in turn, passes its genetic instructions to  ribonucleic acid (RNA)  for directing various metabolic  activities of the cell.  DNA is a polymer of nucleotides (Figure 7 DNA molecule consists of three parts—a nitrogenous  base, a five-carbon sugar called deoxyribose, and a phosphate group. There are four DNA  nucleotides, each with one of the four nitrogenous bases (adenine, thymine, cytosine, and guanine).  The first letter of each of these four bases is often used to symbolize the respective nucleotide (A for  adenine nucleotide, for example).  Figure 7. The molecular structure of nucleotides.
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Unformatted text preview: Figure 8 shows how two strands of nucleotides, paired by weak hydrogen bonds between the bases, form a double-stranded DNA. When bonded in this way, DNA forms a two-stranded spiral, or double helix. Note that adenine always bonds with thymine and cytosine always bonds with guanine. RNA differs from DNA in the following ways: The sugar in the nucleotides that make an RNA molecule is ribose, not deoxyribose as it is in DNA. The thymine nucleotide does not occur in RNA. It is replaced by uracil. When pairing of bases occurs in RNA, uracil (instead of thymine) pairs with adenine. RNA is usually single-stranded and does not form a double helix as does DNA....
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