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Protein Synthesis 3 major processes: Replication DNA copied to form 2 new DNA molecules Nucleus Transcription DNA info copied to RNA Nucleus Translation building a protein according to RNA instructions Cytoplasm Slide 2 DNA Replication Slide 3 Slide 4 DNA Replication = DNA DNA Parent DNA makes 2 exact copies of DNA Occurs in nucleus Why?? Occurs in Cell Cycle before MITOSIS so each new cell can have its own FULL copy of DNA Slide 5 http://www.sumanasinc.com/webcontent/animations/content/meselson.html Models of DNA Replication Slide 6 Slide 7 Segments of single-stranded DNA are called template strands. Copied strand is called the complement strand (think c for copy) BEGINNING OF DNA REPLICATION (INITIATION) DNA helicase (think helix) binds to the DNA at the replication fork (origin of replication) DNA strand separates into TWO untwist (unzips) DNA using energy from ATP by breaking hydrogen bonds between base pairs at several places along the segments of DNA called origins of replication Single-stranded DNA-binding proteins (SSBP) stabilize the single-stranded template DNA during the process so they dont bond back together. Slide 8 DNA Polymerase DNA Polymerase- adds nucleotides to the DNA strands makes POLYNUCLEOTIDES (1 st function) Slide 9 Helicase unzips the DNA molecule DNA Polymerase adds nucleotides to create two NEW identical daughter molecules (A to T) and (G to C) Slide 10 Complementary bases match up Two new strands are formed A with T C with G Slide 11 Slide 12 Elongation Antiparallel nature: Sugar (3end)/phosphate (5 end) backbone runs in opposite directions one strand runs 5 3, other runs 3 5 DNA polymerase only adds nucleotides at the free 3 end of NEW STRAND forming new DNA strands in the 5 3 direction only!!! Slide 13 Slide 14 DNA Replication (Elongation) After SSBPs bind to each template Primase primase is required for DNA synthesis Like a key for a car ignition makes a short RNA primers Short pieces of RNA needed for DNA synthesis DNA polymerase adds nucleotides to RNA primer makes POLYNUCLEOTIDES (1 st function) After all nucleotides are added to compliment strand RNA primer is removed and replaced with DNA by DNA polymerase (2 nd function) DNA ligase seals the gaps in DNA Connects DNA pieces by making phosphodiester bonds Slide 15 Elongation (cont) Leading (daughter) strand NEW strand made toward the replication fork (only in 5 3 direction from the 3 5 template strand Needs ONE RNA primer made by Primase This new leading strand is made CONTINOUSLY Slide 16 Elongation (cont) Lagging (daughter) strand NEW strand synthesis away from replication fork Replicate DISCONTINUOUSLY Creates Okazaki fragments Short pieces of DNA Okazaki fragments joined by DNA ligase Stitches fragments together Needs MANY RNA primer made by Primase Slide 17 3 DNA Polymerase 5 3 Leading strand base pairs 5 3 Supercoiled DNA relaxed by gyrase & unwound by helicase + proteins: Helicase ATP SSB Proteins RNA Primer primase 2 DNA Polymerase Lagging strand Okazaki Fragments 1 RNA primer replaced by DNA Polymerase & gap is sealed by DNA ligase Slide 18 Slide 19 Slide 20 Why Replication again? DNA replication is necessary to create identical copies of DNA so it can be passed onto a new cell (cell division & reproduction) Slide 21 Summary Slide 22 Accuracy of Replication Very low mistake rate (1/billion!) because cells have enzymes (like DNA Polymerase) that proofread, recognize, and fix mistakes! HOWEVER, mistakes can happen MUTATIONS (cancer) Slide 23 Mistakes Made during DNA Replication Mutation Change in DNA (genetic material) Frameshift(s) extra or missing base(s). Substitutions when the wrong nucleotide is incorporated (mismatch mutation). Deletions Nucleotides are deleted shortening the DNA Slide 24 Review: What is DNA replication? 1.A new sugar-phosphate backbone is made for each new strand 2.Base pairs are added 3.Two strands are created in place of the original strand Slide 25