9-DNA.pdf

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SAT II Biology E/M Dr Haitham AbdAllah 01003677719 42 DNA - consists of 2 complementary strands running in opposite directions ( 3' end to 5' end , 5' to 3') . - It is a polymer made of repeating units called nucleotides …. Each nucleotide consists of (5-carbon sugar (deoxyribose), phosphate group , nitrogenous base DNA Replication ( synthesis ) ( during S-phase of interphase ) DNA can replicate itself, it can make exact replica ( copy) of itself when cells want to divide Steps: 1. double helix unwinds and 2 strands separate 2. Next to each separated strand, enzyme called DNA polymerase lines up nucleotides acc. To base pair rulesto form new second strands (complementary strands ) 3. If a strand of DNA to be copied has a nucleotide sequence : AAATCGGAC, Then new strand has the seq. TTTAGCCTG 4. Hydrogen bonds form between base pairs to form ‘’ rungs’’ مللاس of the ladder, bonds form between the sugar-phosphate components بانجلأا of the newly formed nucleotides 5. New double stranded molecules twist up into double helices 6. The 2 new molecules of DNA that are produced, each consists of 1 old strand , 1 new strand . This is called Semi-conservative way ادج ماه * Each separated DNA strand acts as Template ليدوم وا بلاق to form new complementary strand ( new partner )
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SAT II Biology E/M Dr Haitham AbdAllah 01003677719 43 * It means that its bases directs construction of complementary strand alongside it * DNA Polymerase : catalyzes replication and proofreads each new DNA strand, Fixing errors and minimizing occurance of mutations * N.B: Each time DNA replicates, some nucleotides from ends of chromosomes are lost. To protect against possible loss of genes at ends of chromosomes, some eukaryotic cells have special non-
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