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What is replication? - USMF · PDF file What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures

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  • 11/19/2014

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    What is replication?

    Unique property of double stranded molecules of DNA

    Semi-conservative synthesis of DNA based on a template

    Duplication of genetic material

    The main mechanism that assures transmission of information from cell to cell

    and from one generation – to another.

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    Why replication is required?

    Assures exact transmission of

    information

    Determines self-

    reproduction

    Represents the support of heredity

    Assures material linkages between

    generation

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    When replication takes place?

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    What are the principles of replication?

     Based on template;

     Complementary;

     Antiparallel;

     Two directions;

     Semi-conservative;

     Fidel;

     Very complex.

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    Bidirectional synthesis

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    Principles of replication:

    The monomers (nucleotides) are added to 3’ of one strand by enzyme DNA

    polymerase;

    Newly syntheses strand is complementary to template strand;

    Synthesis is semi-conservative: each new double-stranded molecule

    contains an old strand (template strand) a new strand (daughter strand).

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    Semi-

    conservative

    mechanism

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    Components required for replications

    DNA molecule - template

    Origin of replication – point ORI

    Enzymes

    Nucleotides (dNTP and NTP)

    SSB proteins

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    Main enzymes required for

    replication  DNA-polymerase (I, II,

    III – in prokaryotes, a, g, e – in eukaryotes)

     Primase

     DNA-helicases

     Topoisomerase

     DNA-ligase

     Telomerase

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    DNA

    Polymerase

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    Characteristics of eukaryotic

    DNA-polymerases

    DNA polymerase α δ ε β γ

    Location Nucleus Nucleus Nucleus Nucleus Mitochondria

    Synthetic activity Primer

    extension

    Synthesis of

    DNA DNA repair DNA repair Replication

    Additional

    functions - Exonuclease Exonuclease - Exonuclease

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    Topoisomerase

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    Which are the main steps of

    replication?

    Initiation

    Elongation

    Termination

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    Initiation of replication:

    Initiation of polymerization of DNA

    Synthesis of RNA primers

    Formation of replication eye containing two replication forks:

    Unfolding of DNA Denaturation of DNA

    Identification of point ori;

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    Point of initiation of replication - ORI

    • consists of ~300 bp

    • contains sites for interaction with specific proteins required for initiation of replication

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    Elongation

    Enlarging of replication eye;

    Synthesis of DNA in two directions:

    Continuous synthesis of leader strand;

    Interrupted synthesis of lagging strand; synthesis of Okazaki fragments on lagging strand.

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    Termination

    1 mol. DNA 2 mol. DNA.

    Renaturation of DNA;

    Ligation of all fragments;

    Feeling in the gaps;

    RNA primers are removed;

    Meeting of opposite replication forks;

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    The replicon – replication unit

    Contains 100-300 kb.

    Contains ORI point

    Contains two replication forks

    In eukaryotic there are numerous replicons

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    Peculiarities of replication in eukaryotes

    In nucleus replication is carried down by DNA-polymerases a, d

    In mitochondria replication is done by DNA-polymerase g.

    Chromosomal DNA contains many points ORI;

    Replication speed – 20-100 bases/second;

    Human nuclear genome contains 60000 ORI points at every 100- 150 kb.

    Replication of nuclear human DNA is carried out in 6-9 hours 19.11.2014 29

    Example:  If 1st chromosome will contain 1 ori point,

    replication will take place during 15 hours:

    Contains 260 000 000 bp;

    Each replication fork will contain 130 000 000

    bp

    Replication speed - 100 bp/sec;

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    Peculiarities of replication of telomeres

    Telomeres:

    • Sequences of nucleotides at the end of chromosomes;

    • (GGGTTAA)n;

    • Form loops;

    Telomerase:

    • DNA-polymerase RNA-dependent;

    • Contains snRNA – template for synthesis of telomeric DNA.

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    Replication of

    telomeres

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    Werner Patient

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    26 years old

    30 years old

    Doctor and patient – 30 years old 45 years old

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