Replication is the process by which DNA duplicates itself for transmission to daughter cells. It ensures exact transmission of genetic information from one cell generation to the next. Replication involves semi-conservative synthesis of new DNA strands based on existing DNA templates. It requires specific enzymes and occurs through initiation, elongation, and termination steps. Initiation begins at an origin of replication and results in unwinding and denaturation of the DNA helix. Elongation then extends the new strands bidirectionally until replication forks from adjacent origins meet and terminate the process.

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