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CHAPTER 5: BIOLOGY 1 DB014 SEMESTER 1 EXPRESSION OF BIOLOGICAL INFORMATION 5.2 DNA REPLICATION LEARNING OUTCOMES a) Describe semi-conservative replication of DNA b) State the enzymes and proteins i...

CHAPTER 5: BIOLOGY 1 DB014 SEMESTER 1 EXPRESSION OF BIOLOGICAL INFORMATION 5.2 DNA REPLICATION LEARNING OUTCOMES a) Describe semi-conservative replication of DNA b) State the enzymes and proteins involved in DNA replication c) Describe the mechanism of DNA replication and the enzyme involved  SEMI-CONSERVATIVE MODEL Type of DNA replication in which the replicated double helix consists of one old strand, derived from the parental molecule, and one newly made strand  SEMI-CONSERVATIVE MODEL - Two parental strands of parental molecule separate, each functions as a template for synthesis a new, complementary strand. - Each DNA consist of one old strand and one new strand.  DNA REPLICATION Watson and Crick’s Hypothesis Both polynucleotide First step in DNA strands of DNA is replication is complementary to separation of 2 DNA each other strands  DNA REPLICATION Watson and Crick’s Hypothesis Parental / old strands Each parental strand act as template to produce new, complementary strands; according to base-pairing rule New strands  DNA REPLICATION Watson and Crick’s Hypothesis Two identical DNA strands are formed from one DNA strand; each daughter DNA molecule consists of one parental strand and one new strand.  DNA REPLICATION Review Watson and Crick’s Hypothesis 2 daughter DNA New strands Parental strands (act as template)  DNA REPLICATION DNA replication is semi-conservative. Each strand acts as template. Free DNA nucleotide join up to exposed bases by specific base pairing.  Basic Rules of DNA Replication 1. Semi-conservative 2. Starts at the origin 3. Synthesis always in the 5’ to 3’ direction (new strand) 1. Can be unidirectional or bidirectional 2. Primers required  DNA REPLICATION ⮚ 5 enzymes and 1 protein are involved: 1. Helicase 2. Single-strand binding protein 3. Topoisomerase 4. Primase 5. DNA polymerase (I and III) 6. DNA ligase  He said “ Please don’t do lies” Single strand Primase Helicase binding protein He said Please DNA DNA DNA ligase polymerase III polymerase I D on’t Do Lies  1. Helicase Helicase are the enzymes that unwind the double helix strand of DNA by breaking hydrogen bond and separate two parental strand to become single strand.  2. Single-strand binding protein Single-strand binding proteins are the proteins that hold the separated parental strands apart while they act as template.  3. Topoisomerase Topoisomerase are the enzymes that helps relieve the strain caused by unwinding.  4. Primase Primase are the enzymes that catalyze the addition of RNA nucleotides that complementary to the template to form RNA primer.  5. DNA polymerase DNA polymerase are the enzymes that catalyze the synthesis of new DNA by adding nucleotides to the 3’ end of a pre-existing chain. There are two types of DNA polymerase: DNA polymerase III DNA polymerase I  5. DNA polymerase DNA polymerase III adds free DNA nucleotides to the exposed bases by specific base pairing at 3’ end of RNA primer. RNA primer 3’ 5’ DNA polymerase III  5. DNA polymerase DNA polymerase I removes the RNA primer and replace with DNA nucleotides DNA polymerase I I  6. DNA ligase DNA ligase are the enzymes that catalyzed the joining of all Okazaki fragments together to form a continuous strand by formation of phosphodiester bond DNA ligase DNA replication  DNA Replication Process Primase Topoisomerase Helicase replication bubble Single-strand binding protein Step 1: Unwinding of strand DNA replication begins at origin of replication Helicase unwind the double helix strand of DNA and separate two parental strand to become single strand. Forming replication bubble.  DNA Replication Process Primase Topoisomerase Helicase Single-strand binding protein replication fork Step 1: Unwinding of strand At each end of replication bubble is a replication fork. **Replication fork is a Y shape region where parental strands of DNA are being unwound  DNA Replication Process Primase Topoisomerase Helicase Single-strand binding protein DNA template strands Step 2: Strand acts as template When parental strands of DNA are being unwound, both DNA strands act as template Single-strand binding proteins hold the separated parental strands apart while they act as template, keep them from re-pairing.  DNA Replication Process Primase Topoisomerase Helicase Single-strand binding protein DNA template strands Step 2: Strand acts as template The unwinding of double helix causes tighter twisting and strain ahead of replication fork Topoisomerase helps relieve the strain caused by unwinding.  DNA Replication Process Step 3: Synthesis of RNA primer Primase catalyze the addition of RNA nucleotides that complementary to the template to form RNA primer. Primase Topoisomerase Helicase Single-strand binding protein DNA template strands **RNA primer is a short segment of RNA which consist of 5 to 10 nucleotides  Why Priming? This is because DNA polymerase III cannot initiate the synthesis of new DNA strands. They can only add DNA nucleotides to the end of an existing chain that is base-paired with the template strand. The existing chain refer to RNA primer. RNA primer  DNA Replication Process Step 4: DNA nucleotides join up to the exposed bases by specific base pairing - DNA polymerase III adds free DNA nucleotides to the exposed bases by specific base pairing at 3’ end of RNA primer. RNA primer 3’ 5’ DNA polymerase III  DNA Replication Process Step 4: DNA nucleotides join up to the exposed bases by specific base pairing - DNA polymerase III catalyze the elongation of new DNA strand at replication fork only in 5’ to 3’ direction. III 3’ 5’  DNA Replication Process Step 5: Formation of leading and lagging strands from 5’ to 3’ Leading strand synthesized continuously along the template strand which is elongates towards the replication fork. III  DNA Replication Process Step 5: Formation of leading and lagging strands from 5’ to 3’ Lagging strand synthesized discontinuously along the template strand which is elongates in the direction away from the replication fork. III  DNA Replication Process Step 5: Formation of leading and lagging strands from 5’ to 3’ Lagging strand consist of short fragments called Okazaki fragments. III SYNTHESIS OF LEADING STRAND SYNTHESIS OF LAGGING STRAND Reiji Okazaki SYNTHESIS OF LEADING & LAGGING STRAND 3' 5'  DNA Replication Process Step 5: Formation of leading and lagging strands from 5’ to 3’ DNA polymerase I removes the RNA primer and replace with DNA nucleotides I  DNA Replication Process Step 5: Formation of leading and lagging strands from 5’ to 3’ DNA ligase catalyzed the joining of sugar-phosphate backbone of all Okazaki fragments together to form a continuous strand DNA ligase Lagging strand  DNA Replication Process Two identical copies of the original DNA are produced. SUMMARY