Nucleic Acids - Nucleic Acids- DNA & RNA Chapter 08...

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Chapter 08 DNA- Deoxyribonucleic Acid Double stranded chains of pentose sugars (deoxyribose), separated by phosphate (PO 4 ) groups and cross- linked by pairs of nitrogenous bases, which are: Purines - Adenine and Guanine Pyrimidines - Thymine and Cytosine This cross-linkage is formed by pairing A with T, and G with C; no other pairings are possible in DNA. The pentose sugars are separated by phosphate groups to form the outsides of a long ladder-like double chain, cross-linked by the nitrogenous bases. Watson and Crick built on the work of Linus Pauling, Maurice Wilkins and Rosalind Franklin to determine the structure of the genetic material. They won the 1962 Nobel prize in Biochemistry for their work. DNA molecules control the metabolism of all living cells, by controlling the synthesis of proteins- most of which are ENZYMES- the tools used by cells for all cell functions. The genetic code contained by genes is a series of directions for assembly of proteins- blueprints for ENZYMES. DNA - The Semi-Conservative Method of Replication Each of the two sides of the double helix is a mirror image of the other; each side can be used as a pattern to replicate its’ complementary strand. This how DNA strands contain all the information required to replicate themselves. Enzymes called DNA helicase unwind the coiled double helix of DNA, beginning at the point called the replication fork. DNA polymerase enzymes separate the complementary DNA strands; this results in one 5’ to 3’ strand and one 3’ to 5’ strand. Then assembly of two new complementary strands can occur; each separated strand is used as a template for synthesis of a new complementary strand. This means that the original 3’ to 5’ strand is used to synthesize a new 5’ to 3’ DNA strand and the original 5’ to 3’ strand is used to build a new 3’ to 5’ strand of DNA. DNA polymerase is the enzyme that assembles new nucleotides by attaching nitrogenous bases to the deoxyribose sugar rings to build nucleotides. DNA polymerases can attach new nucleotides only from the 5’—3’ direction . Synthesis will proceed in opposite directions along the complementary strands of DNA. . This results in two identical strands of DNA—each with one “original” string of sugars and Nucleotide bases and one complementary “daughter” strand, cross-linked by the complementary nucleotides. This is called the “semi-conservative” model of DNA replication. One strand is synthesized continuously, in the 5’---> 3’ direction ; the other strand is synthesized in small fragments , which are then bonded together by DNA ligase enzymes to build the complementary strand. Replication on the 3’-->5’ strand (lagging strand) requires the synthesis of an RNA “primer” by the enzyme RNA polymerase , which “reads” a 3-nucleotide segment of the 3’--->5’ strand and synthesizes a
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Nucleic Acids - Nucleic Acids- DNA & RNA Chapter 08...

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