Dna

Duplicate of original molecule

Figure 7.1 Overview of Replication, Transcription, and Translation DNA

replication is the process that duplicates DNA so that its encoded information can be passed on to future generations.Transcription is the process that copies the genetic information into a transitional form, RNA.Translation is the process that deciphers the encoded information to synthesize a specific protein.

each sugar is one of the nitrogenous bases, an adenine (A), thymine (T), guanine (G), or cytosine (C). Because of the chemical structure of the nucleotides and how they are joined, a single strand of DNA will always have a 5'PO4 group at one end and a 3'OH group at the other. These ends are often referred to as the 5' end and the 3' end and have important implications in DNA and RNA synthesis that will be discussed later. ■ deoxyribonucleic acid (DNA), p. 31 ■ nucleotides, p. 31

The DNA in a cell usually occurs as a double-stranded, helical structure (figure 7.2). The two strands are held together by weak hydrogen bonds between the nitrogenous bases of the opposing strands. While individual hydrogen bonds are readily broken, the duplex structure of double-stranded DNA is quite stable because of the sheer number of bonds that occurs along its length. Because short fragments of DNA have correspondingly fewer hydrogen bonds, they are readily separated into single-stranded pieces. Separating the two strands is called denaturing. ■ hydrogen bonds, p. 21

The two strands of double-stranded DNA are complementary (figure 7.3). Wherever an adenine is in one strand, a thymine is in the other; these two opposing nucleotides are held together by two hydrogen bonds between them. Similarly, wherever a cytosine is in one strand, a guanine is in the other. These are held together by the formation of three hydrogen bonds, a slightly stronger attraction than that of an A:T pair. The characteristic bonding of A to T and G to C is called base-pairing and is fundamental to the remarkable functionality of DNA. Because of the rules of base-pairing, one strand can always be used as a template for the synthesis of the complementary opposing strand. ■ complementary, p. 33

While the two strands of DNA in the double helix are complementary, they are also antiparallel. That is, they are oriented in opposite directions. One strand is oriented in the 5' to

Nester-Anderson-Roberts: I I. Life and Death of I 7. The Blueprint of Life, I I © The McGraw-Hill

Microbiology, A Human Microorganisms from DNA to Protein Companies, 2003

Perspective, Fourth Edition

A highly coiled line is used to depict genomic DNA.

A highly coiled line is used to depict genomic DNA.

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