2. 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.

3. Why replication is required?
 Assures exact transmission of
information;
 Determines self-reproduction;
 Represents the support of heredity;
 Assures material linkages between
generation.

4. When replication takes place?

5. What are the principles of replication?
 Based on template;
 Complementary;
 Antiparallel;
 Two directions;
 Semi-conservative;
 Fidel;
 Very complex.

7. Bidirectional synthesis

8. 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).

9. Semiconservative
mechanism

11. Components required for
replications
 DNA molecule - template
 Origin of replication – point ORI
 Enzymes
 Nucleotides (dNTP and NTP)
 SSB proteins

13. Main enzymes required for
replication
 DNA-polymerase
(I, II, III – in
prokaryotes,
– in
eukaryotes)
 Primase
 DNA-helicases
 Topoisomerase
 DNA-ligase
 Telomerase

14. DNA
Polymerase

16. Topoisomerase

17. What are the main steps of
replication?
 Initiation
 Elongation
 Termination

18. Initiation of replication:
 Identification of point ori;
 Formation of replication eye containing two
replication forks:
 Unfolding of DNA
 Denaturation of DNA
 Synthesis of RNA primers
 Initiation of polymerization of DNA

19. Point of initiation of replication - ORI
• consists of ~300 bp
• contains sites for interaction with specific proteins
required for initiation of replication

21. 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.

25. Termination
 Meeting of opposite replication forks;
 RNA primers are removed;
 Feeling in the gaps;
 Ligation of all fragments;
 Renaturation of DNA;
1 mol. DNA  2 mol. DNA.

26. The replicon – replication unit
• Contains 100-300 kb.
• Contains ORI point
• Contains two replication forks
• In eukaryotic there are numerous
replicons

27. 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

28. Peculiarities of replication in
eukaryotes
In nucleus replication is carried down by DNApolymerases
 In mitochondria replication is done by DNApolymerase .
 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

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;

30. 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.

31. Replication of
telomeres

32. Werner Patient

33. 30 years old
Doctor and patient –
30 years old
26 years old
45 years old