8.3 DNA Replication Essential Idea Genetic information in DNA can be accurately copied and can be translated to make the proteins needed by the cell.

8.3 DNA Replication Understandings The replication of DNA is semi-conservative and depends on complementary base pairing. Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds. DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template.

DNA Replication 5 end 3 end 5 end 3 end Space-filling modelPartial chemical structure Hydrogen bond Key features of DNA structure 0.34 nm 3.4 nm 1 nm

DNA REPLICATION Introduction. A single strand of DNA serves as a template for a new strand. The rules of base pairing direct replication. DNA is replicated during the S (synthesis) stage of the cell cycle. Each body cell gets a complete set of identical DNA.

8.3 DNA Replication IB Assessment Statement Explain DNA replication in terms of unwinding the double helix and separation by helicase followed by the formation of the new complimentary strands by DNA polymerase.

DNA REPLICATION INTRODUCTION DNA serves only as a template. Enzymes and other proteins do the actual work of replication. –Enzyme (Helicase) unzip the double helix. –Free-floating nucleotides form hydrogen bonds with the template strand. nucleotide The DNA molecule unzips in both directions.

–Polymerase enzymes form covalent bonds between nucleotides in the new strand. –DNA polymerase enzymes bond the nucleotides together to form the double helix. DNA polymerase new strand nucleotide

DNA Replication UNZIPPING DNA How Replication Occurs DNA replication is carried out by enzymes that “unzip” a molecule of DNA. Hydrogen bonds between base pairs are broken and the two strands of DNA unwind.

Replication Fork The location where the DNA is unwinding is called the replication fork Nitrogen Bases Replication Fork DNA Polymerase Replication Fork Original strand New Strand Growth

Hydrogen bonds are broken –Enzyme helicase aids in breaking bonds which allows strands to separate. –Single strand binding proteins (SSB's) keep strand from joining back together. –Replication Fork is Formed. nucleotide The DNA molecule unzips in both directions.

Adding new nucleotides to the strands of DNA The principal enzyme involved in DNA replication is DNA polymerase. DNA polymerase joins individual nucleotides to produce a DNA molecule and then “proofreads” each new DNA strand. DNA polymerase new strand nucleotide

Nitrogen Bases Replication Fork DNA Polymerase Replication Fork Original strand New Strand Growth

DNA replication is semiconservative. Semiconservative means that each DNA molecule contains one new strand of DNA and one old strand of DNA. original strand new strand Two molecules of DNA Two new molecules of DNA are formed, each with an original strand and a newly formed strand.

8.3 DNA Replication Nature of Science & SKILLS Obtaining evidence for scientific theories—Meselson and Stahl obtained evidence for the semi-conservative replication of DNA. (1.8) Skill: Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA.

8.3 DNA Replication Skills and Applications Application: Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR). (We will cover this in Unit 3.5 Genetics) Application: Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species. (We will cover this is Unit 3.5 Genetics)