DNA Replication [The Central Dogma of Biology]

    Cards (55)

    • DNA Replication
      • A process in which a dividing cell generates a copy of its DNA.
      • ○ Resulting product is two identical DNA molecules produced from a single original DNA.
      • Before a cell divides, it must first copy (or replicate) its entire genome so that each resulting daughter cell ends up with its own complete genome.
    • Location of the DNA Replication
      • Eukaryotic Cells - nucleus
      • Prokaryotic Cells - cytoplasm
      • ○ Prokaryotic cells don’t have a nucleus
    • Models of Replication
      • Each short segment of double helix symbolizes the DNA within a cell. Beginning with a parent cell, we follow the DNA for two more generations of cell - two rounds of DNA replication.
      • Conservative Model
      • Semiconservative Model
      • Dispersive Model
    • Conservative Model
      • Two parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix.
    • Semiconservative Model
      • Two strands of the parental molecule separate, and each functions as a template for synthesis of a new, complementary strand.
      • Half of the strand is conserved while the other is not
      • DNA replicates through this model
    • Dispersive Model
      • Each strand of both daughter molecules contains a mixture of an old and new synthesized DNA
      • Smaller fragments of original DNA are dispersed.
    • Key Enzymes of Replication Process
      • Helicase
      • DNA Polymerase
      • Primase
      • Ligase
    • Enzyme
      • Molecules that speed up the rate of chemical reaction
      • usually ends in -ase
    • Helicase
      • the “unzipping” enzyme
      • unzips/separates the double helix by breaking the hydrogen bonds between the complementary bases
    • DNA Polymerase
      • the “builder” enzyme
      • replicates the DNA molecules to build a new strand
    • Primase
      • the “initializer” enzyme
      • synthesizes short RNA sequences called “primers”
      • Primers - serve as a starting point for DNA to synthesis
      • they are made out of RNA
    • Ligase
      • the “gluer” enzyme
      • an enzyme which connects two strands of DNA together
    • Process of DNA Replication
      • Origin of Replication
      • Forming of Replication Fork
      • Initiation Stage
      • Synthesizing of New DNA Strand
      • Antiparallel Elongation
      • Replacing RNA Primers
      • Proofreading and Correcting DNA
    • Process of DNA Replication
      Origin of Replication
      • Starting point of DNA Replication
      • Where 2 DNA strands are separated and the opening up of replication bubbles
      • Number of Origins
      • ○ Eukaryotic Cell - multiple origins
      • ○ Prokaryotic Cell - one origin
      • There are multiple origins of replication along the DNA strand that makes the replication work simultaneously in different places of the DNA.
    • Process of DNA Replication
      Forming of Replication Fork
      • At each end of replication bubble is a replication fork
      • ○ A Y-shaped region where the parental strands of DNA are being unwound.
    • Process of DNA Replication
      Initiation Stage
      • Helicase
      • Single-strand binding proteins
      • Topoisomerase
    • Process of DNA Replication
      Initiation Stage
      Helicase
      • Enzyme that untwists the double helix at the replication forks, separating the two parental strands and making them available as template strands
      • Finds the origin of replication and starts the initiation process of DNA replication.
      • Destroys the hydrogen bonding
      • ■ the weakest bond-making enzyme is easy to enter
    • Process of DNA Replication
      Initiation Stage
      Single-strand Binding Proteins
      • Binds and stabilizes single-stranded DNA
      • Keeps DNA from re-pairing or degradation
      • ”to keep them separated”
    • Process of DNA Replication
      Initiation Stage
      Topoisomerase
      • Enzyme that relieves the strain by breaking, swiveling, and rejoining DNA strands.
      • Binds to the overwhelmingly strand and cut the tension
      • ”to avoid supercoiling”
    • Process of DNA Replication
      Synthesizing of New DNA Strand
      • Primase
      • Primer
      • DNA Polymerase III
      • Nucleoside Triphosphate
    • Process of DNA Replication
      Synthesizing of New DNA Strand
      Primase
      ○ It starts with a complementary RNA chain with a single RNA nucleotide and
      add RNA nucleotides one a time using the parental DNA strand as a template
      ○ Completed primer is short (5-10 nucleotides long)
    • Process of DNA Replication
      Synthesizing of New DNA Strand
      Primer
      ○ The “RNA Chain”
      ○ Will attach to the 3’ end because it serves as the starting point of the new
      DNA strand
      ○ Rate of elongation is about 500 nucleotides per second in
      bacteria(prokaryotic) and 50 per second in human cells
      ■ replication is faster in the prokaryotic cells
    • Process of DNA Replication
      Synthesizing of New DNA Strand
      DNA Polymerase III
      ○ Catalyze the synthesis of new DNA by adding nucleotide to the 3’ end of a pre-existing chain
    • Process of DNA Replication
      Synthesizing of New DNA Strand
      Nucleoside Triphosphate
      ○ The nucleotide that is added to a growing DNA strand
      ○ Nucleoside = sugar + nitrogenous bases, no phosphate backbone
    • Process of DNA Replication
      Synthesizing of New DNA Strand
      • DNA Polymerase catalyzes addition of a nucleotide to the 3’ end of a growing DNA strand, with the release of two phosphates.
    • Process of DNA Replication
      Antiparallel Elongation
      • Leading Strand
      • Lagging Strand
      • Okazaki Fragments
    • Process of DNA Replication
      Antiparallel Elongation
      • Because of their structure, DNA polymerase can add nucleotides only to the free 3’ end of a primer or growing DNA strand, never to the 5’ end.
      • Thus, a new DNA strand can elongate only in the 5’->3’ direction.
    • Process of DNA Replication
      Antiparallel Elongation
      Leading Strand
      ○ Strand that continuously adds nucleotide to the new complementary strand as the fork progresses
      ○ Continuous synthesis
    • Process of DNA Replication
      Antiparallel Elongation
      Lagging Strand
      ○ Strand elongates away from the replication fork
      ○ Synthesized discontinuously, as a series of fragments called: okazaki fragments
    • Process of DNA Replication
      Antiparallel Elongation
      Okazaki Fragments
      ○ after Reiji Okazaki
      ○ fragments are about 1,000-2,000 in prokaryotes and 100-200 nucleotides long in eukaryotes
    • Process of DNA Replication
      Replacing RNA Primers
      • DNA Polymerase I
      • DNA Ligase
    • Process of DNA Replication
      Replacing RNA Primers
      DNA Polymerase I
      • Used to remove the primase and replace it with DNA
    • Process of DNA Replication
      Replacing RNA Primers
      DNA Ligase
      ○ Enzyme that will link all the Okazaki fragments
    • Process of DNA Replication
      Proofreading and Correcting DNA
      • DNA Polymerase
      • Nucleotide Excision Repair
      • Mismatch Repair
    • Process of DNA Replication
      Proofreading and Correcting DNA
      DNA Polymerase
      Proofreads the newly made DNA by replacing any incorrect nucleotides
    • Process of DNA Replication
      Proofreading and Correcting DNA
      Nucleotide Excision Repair
      ○ Process of repairing incorrect nucleotides
      ○ A segment of strand containing the damage is excised by a DNA-cutting enzyme called nuclease
      ○ The result gap from the nuclease is filled with nucleotides, using strand as a template via enzymes DNA polymerase and ligase.
    • Process of DNA Replication
      Proofreading and Correcting DNA
      Mismatch Repair
      • Other enzymes remove and replace incorrectly paired nucleotides that have resulted from replication errors.
    • Importance of DNA Replication
      • The process of DNA replication helps in the inheritance process by transfer of the genetic material from one generation to another.
      • ○ Therefore, it is required for the growth, repair, and regeneration of tissues in living organisms.
      • Due to the process of DNA replication, each daughter cell gets an equal amount of DNA.
    • Prokaryotic
      • Site of replication is in the cytoplasm
      • DNA replication is the first step in cell division that is in binary fission
      • One origin of replication(ori) per DNA molecule. Replication occurs at one point in each prokaryotic DNA molecule.
      • Origin is formed of approximately 100-200 or more nucleotides
      • Two replication forks and one replication bubble is formed
      • Okazaki fragments are longer. (1000-2000 nucleotides)
      • Replication is more accurate and rapid. (2000 bp/s)
      • Simple and less complex
    • Eukaryotic
      • Occurs in the nucleus
      • Occurs during interphase or S(synthesis) phase in the cell cycle
      • Many over 1000 ori in each eukaryotic chromosome.
      • Replication occurs at several points simultaneously.
      • Each origin is formed of approximately 150 nucleotides
      • Vast number of replication forks and replication bubbles
      • Okazaki fragments are shorter (100-200 nucleotides)
      • Replication is slow. (100 bp/s)
      • Complex and involves various stages of mitosis