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11/19/2014 1 19.11.2014 1 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. 19.11.2014 2 Why replication is required? Assures exact transmission of information Determines self- reproduction Represents the support of heredity Assures material linkages between generation 19.11.2014 3

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

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Page 1: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

11/19/2014

1

19.11.2014 1

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.

19.11.2014 2

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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Page 2: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

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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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Page 3: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

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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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Page 4: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

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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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Page 5: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

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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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Page 6: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

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Characteristics of eukaryotic

DNA-polymerases

DNA polymerase α δ ε β γ

Location Nucleus Nucleus Nucleus Nucleus Mitochondria

Synthetic activityPrimer

extension

Synthesis of

DNADNA repair DNA repair Replication

Additional

functions- Exonuclease Exonuclease - Exonuclease

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Topoisomerase

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Page 7: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

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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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Page 8: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

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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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Page 9: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

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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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Page 10: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

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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 hours19.11.2014 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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Page 11: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

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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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Page 12: What is replication? - USMF · What is replication? ... Semi-conservative synthesis of DNA based on a template Duplication of genetic material The main mechanism that assures transmission

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26 years old

30 years old

Doctor and patient –30 years old 45 years old

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