We are now beginning our study of viruses and need to review the structures
and functions of DNA and RNA.
|DNA is used to transfer information from one generation to another.||RNA is used to take the information from DNA and use it to make proteins. Proteins control many of the chemical reactions that occur in cells.|
|The structure of a DNA molecule is called a double helix (a twisted ladder). The two halves of the DNA "ladder" are long strings of building blocks called nucleotides.||RNA molecules are single-stranded polymers of nucleotides also. These molecules could be describes as "half-ladders."|
|Each nucleotide in a DNA molecule consists of three parts, a sugar (deoxyribose), a phosphate group, and a nitrogen base.||Each nucleotide in an RNA molecule consists of three parts, a sugar (ribose), a phosphate group, and a nitrogen base.|
|The sides of a DNA "ladder" consist of alternating sugar and phosphate groups. Each "rung" consists of nitrogen base pairs.||The side of an RNA "half-ladder" consists of alternating sugar and phosphate groups, Each half-rung consists of one nitrogen base.|
|In DNA there are four different kinds of nitrogen bases, adenine (A), guanine (G), cytosine (C) and thymine (T).||In RNA there are four different kinds of nitrogen bases, adenine (A), guanine (G), cytosine (C), and uracil (U).|
|In DNA "rungs," adenine always pairs with thymine and cytosine always pairs with quanine.||When DNA is used as a template to produce RNA (during transcription), guanine always pairs with cytosine. Thymine on the DNA pairs with adenine on the RNA. But adenine on the DNA pairs with uracil on the RNA.|
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