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# DNA Replication - Topoisomerase - uncoils DNA and of - Primase - adds RNA primers to start off - DNA polymerase - attaches complementary nucleotides in 5' to 3' direction - DNA ligase - fills in gaps and ligates strands ## The Important of DNA - DNA is present in all cells - DNA is made up of nu...

# DNA Replication - Topoisomerase - uncoils DNA and of - Primase - adds RNA primers to start off - DNA polymerase - attaches complementary nucleotides in 5' to 3' direction - DNA ligase - fills in gaps and ligates strands ## The Important of DNA - DNA is present in all cells - DNA is made up of nucleotides - DNA contains the info to make proteins - DNA contains genetic information that is passed on from parent to offspring ## What Does DNA Do? - DNA stores genetic information - is a set of instructions to which make proteins - is passed down to next generation - DNA needs to be copied - Every time a cell divides, DNA needs to be copied - Genes encode proteins, which are expressed in a two-step process: - transcription DNA to RNA - translation RNA to protein ## The Structure of DNA - 5’ end has phosphate group - 3’ end has OH - A - T pairing, G - C pairing - DNA strands run in opposite direction (antiparallel) ## The Sugar Phosphate Backbone - 2 ends of DNA backbone: - 5’ end w phosphate group - 3’ end w OH - 2 strands are anti parallel - New nucleotide is added to 3’ end so DNA chain grows in 5’ to 3’ direction ## DNA Replication - Process of making another copy of DNA - Breaks the hydrogen bonds between 2 strands - Each parent strand serves as template for new strand - Serves as a template for new replicated DNA molecule - A - T, G - C base pairing - Replicated DNA molecule is half "old" ½ half "new" ### Semiconservative replication - A lot of enzymes are needed for DNA replication - **Helicases** - unzips the 2 strands - breaks bonds between bases of the 2 strands - Half of replication bubble is called replication fork - leading strand is synthesized continuously - lagging strand is synthesized in fragments ### The Polymerase Chain Reaction (PCR) - Laboratory technique used to make many copies of a DNA fragment (amplification) - Repeat denaturation and extension steps of DNA replication ### Gel Electrophoresis - Gel electrophoresis allows scientists to see, analyze DNA fragments - Electrical current moves fragments through a special gel that sorts the DNA - DNA has overall negative charge due to its backbone so it **moves toward positive charge** ### DNA Sequencing - Process of determining the sequence of nucleotides (A.T.C.G) in given DNA fragment - There are many types of DNA sequencing using diff technologies. - Lasers are used to excite fluorescently labeled DNA fragments, which then emit light that is detected by cameras or other photodetectors ## Errors in DNA Replication (can occur mistakes) - if mistake isn't corrected, mutation in the DNA occurs. - Wrong info is then encoded in defective protein which can be expressed. ### What can cause errors during DNA replication? - **Polymerase mistake rate**: 1 per every 100,000 nucleotides - In humans, w our 6 billion base pairs in a cell ~120,000 mistakes every time DNA replicates for cell division - **Other replication stress factors**: interferences w DNA replication - Unusual DNA structures - Certain repetitive DNA sequence