Monomer Nucleotide 3 Parts Backbone Phosphate Ribose Sugar Center Nitrogenous Base Purine Purine too wide Adenine A Thymine T Guanine G Cytosine C Antiparallel arrangement and twisted feature of DNA DNA Notation 5 and 3 refer to number of carbon with either the phosphate 5 or hydroxyl group 3 1 5 to 3 if single strand 2 If written as double strand the top strand is written 5 to 3 5 3 3 5 Replication Human Genome 46 Chromosomes 4 6 origins of replication Origin of Replication Generally A T 2 hydrogen bonds rich WHY Fewer hydrogen bonds easier to pull it apart where as G C 3 hydrogen bonds Single in prokaryotes multiples in eukaryotes WHY DNA always synthesized by adding bases to the 3 end 5 to 3 elongation Stage Leading Strand Lagging Strand The Cast DNA Polymerase building the DNA adding the nucleotides synthesizes the DNA Topoisomerase untwists the kinks the helix Helicase breaks apart the phosphodiester bonds to open the double helix Single Stranded DNA Binding Proteins stabilizes single stranded binding proteins DNA Ligase Primers short fragment of RNA ribonucleic acid DNA replication depends on it occurs in both directions leading and lagging strand RNA Primase Telomerase enzymes that provide telomeres extends unrelipcated ends codes of junk and sequences that we can afford to lose Replisome large complex where both leading and lagging strands are being processed semiconservative replication occurs at each end of the replication fork Circular DNA vs Linear DNA Telomeres repeating sequences at end of DNA strands Flag the end as normal and not a break in chromosomes Protect against erosion during replication o May serve as biological clock in somatic cells o Active in cancer cells Can you chemically tell the difference between the leading strand and lagging strand DNA picks up methyl groups and radioactivity Clicker Question Which of the following statements about the replication of DNA is false Clicker Question Answer New nucleotides are added to the most 3 end of one strand and the most 5 end of the other strand At the end of DNA replication but before cell division the nucleus contains 4 copies of every gene diploid chromosomes Problem with Linear Replications Problems with copying the ends of linear chromosomes Lagging strand is completed DNA Polymerase III adds a mismatched base sometimes notices the mistake and corrects it No system is 100 correct Mistakes Happen Mismatch wrong base is chosen in daughter strand Fix proofreaders remove it resume synthesis Insertion Deletion No proofreaders is perfect Polymerase errors cause mutations Beneficial deleterious neutral Adds nucleotides to RNA primer DNA polymerase III Removes RNA primer and replaces with Silent Mutation changes the 3rd nucleotide in the codon no effect on amino acid sequence Missense Mutation changes the first nucleotide in the codon may change the amino acid May be beneficial deleterious or harmful Frameshift Deletion 1 base pair is deleted that could change the rest of the polypeptides Nonsense Mutation produces a stop codon very early in the polypeptide chain Frameshift Insertion 1 base pair insertion that could produce a stop codon nonsense No Frameshift 3 base pair deletions one whole amino acid is missing
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