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DNA & DNA Replication History DNA Comprised of genes In non-dividing cell nucleus as chromatin Protein/DNA complex Chromosomes form during cell division Duplicate to yield a full set in daughter cell From Chapter 3 Nucleic acids are polymers Monomers are called nucleotides Nucleotides = base + sugar + phosphate Base = adenine, guanine thymine, cytosine, uracil Sugar = deoxyribose or ribose Phosphate, a single phosphate in DNA Sugar is linked to the phosphate DNA is a Double Helix Nucleotides A, G, T, C Sugar and phosphate form the backbone Bases lie between the backbone Held together by H-bonds between the bases A-T – 2 H bonds G-C – 3 H bonds H - Bonds Base-pairing rules AT only (AU if DNA-RNA hybrid) GC only Double Helix Nucleotides as Language We must start to think of the nucleotides – A, G, C and T as part of a special language – the language of genes that we will see translated to the language of amino acids in proteins Genes as Information Transfer A gene is the sequence of nucleotides within a portion of DNA that codes for a peptide or a functional RNA Sum of all genes = genome DNA Replication Semiconservative Daughter DNA is a double helix with 1 parent strand and 1 new strand Found that 1 strand serves as the template 3’ for new strand 5’ Parental DNA Molecule Replication Fork 3’ 5’ DNA Template Each strand of the parent DNA is used as a template to make the new daughter strand DNA replication makes 2 new complete double helices each with 1 old and 1 new strand How is DNA Synthesized? DNA is synthesized by Simple addition of nucleotides along one strand (1/2 the double helix) Mistakes during Replication Base pairing rules must be maintained Mistake = genome mutation, may have consequence on daughter cells Only correct pairings fit If wrong nucleotide is included Special enzyme has “proofreading” and can remove incorrect nucleotide Another enzyme then adds correct base Proofreading Other Necessary Proteins Helicase opens the double helix and helps it uncoil Specialized binding proteins keep strands separated DNA Repair For the rare mutations occurring during replication that isn’t caught by DNA proofreading enzyme If no repair In germ (sex) cells inherited diseases In somatic (regular) cells cancer Effect of Mutation Repair Mechanisms Different enzymes correct different mistakes Other enzymes make the proper strand piece Still another enzyme will join new the new piece in its proper spot on the strand