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  1. 1. DNA Respiration Model Alexis vite KEY Guanine Thymine Adenine Cytosine
  2. 2. Origins of replication Replication Bubbles: Hundreds of replicating bubbles (eukaryotes) (Prokaryotes) Single replication fork (bacteria) Parental Strand Origin of replication Daughter strand Bubble In Eukaryotes, DNA replication begins at many sites along the giant DNA molecule of each chromosome. Bubble Replication Fork
  3. 3. Strand Seperation: 1.Helicase: enzyme which catalyze the unwinding and separation (breaking H- Bonds ) of the parental double helix. 2. Single- Strand Binding Proteins: proteins which attach and help keep the separated strands apart. Unwind DNA Helicase enzyme unwinds part of DNA helix stabilized by single-stranded binding proteins 3. Semi-conservative replication 1. Each new DNA molecule contains one old strand & one old strand
  4. 4. 1. Complementary base pairing DNA Guanine- a compound that occurs in guano and fish scales, and is one of the four constituent bases of nucleic acids. A purine derivative, it is paired with cytosine in double-strand DNA. 5’ 3’ G-C Thymine- a compound that is one of the four constituent bases of nucleic acids. A pyrimidine derivative, it is paired with adenine in double-stranded DNA. T-A C-G A-T T-A Adenine- a compound that is one of the four constituent bases of nucleic acide. A purine derivative,it is paired with thymine in double-stranded DNA. T-A G-C A-T 3’ Makes replication possible C-G A-T 5’ Cytosine- A compound found in living tissue as a constituent base of nucleic acids. It is paired with guanine in doublestranded DNA.
  5. 5. Base Pairing in DNA Purines Adenine(A) Guanine(G) Pryimidines Thymine(T) Cytosine (C) Pairing A:T 2 bonds C:G 3 bonds Two strands coiled called a double helix Sides made of a pentose sugar Deoxyribose bonded to phosphate (po4) groups by phosphodiester bonds. Center made of nitrogen bases bonded together by weak hydrogen bonds.
  6. 6. Enzyme DNA Enzyme Topoisomerase attaches to the forks of the bubble to relieves stress on the DNA Molecule by allowing free rotation around a single strand.
  7. 7. DNA 5’ 3’ T-A C-G A-T 3’ 5’ G-C T-A DNA Helicase (unwinds DNA) C-G A-T T-A T-A T-A Parental DNA molecule G-C Origins of replication Replication Forks: hundreds of Y-shaped regions of replicating DNA molecules where new strands are growing. 1. Uncoil & unzip DNA molecule enzyme breaks weak 2. Hydrogen Bond between bases T -A G-C A-T Starts in origin of Replication helicase 5’ 3’ 5’ Begins at Origins of Replication Two strands open forming Replication Forks (y-shaped region) New strands grow at the forks. G-C A-T 3’ Replication Fork
  8. 8. DNA polymerase Sugar-Phosphate backbone 5’ 3’ Reads 3’- 5’ synthesises 5’3’ G-C Base Pair (Joined by Hydrogen bonding) Old Strand T-A C-G Replication of DNA *base pairing allows each strand to serve as a template for a new strand. T-A T *new strand is ½ parent template & ½ new DNA. Nucleotide about to be added to a new strand A-T A-T Each parent strand remains intact G-C 5’ New Strand 3’ Every DNA molecule is half “old” and half “new”
  9. 9. Synthesis of the new DNA Strands: DNA Polymerase: with a RNA primer in place, DNA Polyymerase (enzyme) catalyze the synthesis of a new DNA strand in the 5’ to 3’ direction. 5’ 3’ 5’ Nucleotide DNA Polymerase RNA Primer
  10. 10. Leading Strand: The leading Strand is synthesized as a single strand from the point of origin toward the opening replication fork. 5’ 3’ 5’ Nucleotide DNA Polymerase RNA Primer
  11. 11. Synthesis of the New DNA Strands The Lagging Strand is synthesized discontinuously against overall direction of replication This strand is made in MANY short segments it is replicated from the replication fork toward the origin. Leading Strand 5’ 3’ 5’ DNA Polymerase RNA Primer 3 ’ 5’ 5’ 3’ Lagging strand
  12. 12. Okazaki Fragments: series of shore segments on the lagging Strand. Must be joined together by an enzyme. Okazaki Fragment DNA Polymerase RNA Primer 3 ’ 5’ 5’ 3’ Lagging Strand
  13. 13. DNA ligase: a linking enzyme that catalyzes the formation of a covalent bond from the 3’ to 5’ end of joining strands Example: joining two Okazaki fragments together. DNA ligase Okazaki Fragment 1 Okazaki Fragment 2 3 ’ 5’ 5’ 3’ Lagging Strand
  14. 14. Double Helicase Strand 5’ 3’ 5’ G-C 3’ G-C T-A C-G A-T A-T T-A T-A T-A T-A G-C G-C A-T 3’ T-A C-G Sugar phosphate backbone A-T 5’ 3’ 5’ Base Pairs Guanine Thymine Adenine Cytosine