1. Structure and functions of nucleic acids. DNA replication.

2. History of DNA research
1868 – discovery of nucleic acids (F. Miescher)
1889 – the term "nucleic acid“ was coined (R. Altmann)
– study of DNA primary structure (Ph. A. Levene, A. Todd)
1928 – Griffith's experiment
1944 – O. Avery, C. MacLeod, and M. McCarty proved that DNA is the biomolecule responsible for heredity.
1952 – A. Hershey and M. Chase confirmed the idea that DNA is the genetic material.

3. Functions of nucleic acids
Storage of genetic information
Transmission of genetic information
Expression of genetic information

4. Nucleic acids are biopolymers made up of monomers called nucleotidesNA
DNA RNA
Deoxyribonucleic acid Ribonucleic acid

5. Pentoses DNA RNA

8. The primary structure of NA
The primary structure of NA is the sequence of nucleotides.
The linkage between two mononucleotides is called a 3’-,5’- phosphodiester bond.

9. Chargaff's rules (E. Chargaff, 1950)
[А] = [T]
[G] = [C]
[A + G] = [T + C]
[A + T] ≠ [G + C]

10. The secondary structure of DNA a double helix (J. Watson and F
The secondary structure of DNA a double helix (J. Watson and F. Crick, 1953)
This model has the following major features:
Two long polynucleotide chains are coiled around a central axis, forming a double helix.
The two chains are antiparallel; that is, their 5’ to 3’ orientations run in opposite directions.
The bases of both chains are flat structures lying perpendicular to the axis.
The nitrogenous bases of opposite chains are paired as the result of the formation of hydrogen bonds; A -T and G -C pairs occur (Complementary base pairing).

12. Forms of DNA A B C Z Right-handed Left-handed 10,7 10,0 9,3 12 +33,6°
Helix direction
Right-handed
Left-handed
Number of base pairs per complete turn
10,7
10,0
9,3 12
Rotation per base pair
+33,6°
+36,0°
+38,6°
-30°
Distance between adjacent bases
0,23 nm
0,34 nm
0,3 nm
0,38 nm
Helical diameter
2,3 nm
2,0 nm
1,9 nm
1,8 nm

13. Classes of RNA
mRNAs carry genetic information from the DNA of the gene to the ribosome (5%).
rRNAs are important structural components of ribosomes (80%).
tRNAs carry amino acids to the ribosome during translation; recognize and decode an mRNA codon (10%).
snRNAs participate in processing mRNAs .
microRNAs, siRNAs are involved in gene regulation.
primers are involved in DNA replication.
telomerase RNA is involved in DNA replication at the ends of chromosomes
viral RNA is genetic material of some viruses.

14. a clover-leaf structure
Structure of t-RNA
Secondary
Tertiary
L-form
 a clover-leaf structure

15. DNA replication
DNA replication is the process of producing two identical replicas from one original DNA molecule (M. Meselson and F. Stahl, 1958; А. Kornberg, 1959)

16. Initiation (preparing of the template)
Origin (Ori) is a particular sequence at which replication is initiated ( bp which contains A–T rich repeats)
+ initiator protein (Dna A) recognizes Ori-site and promotes the unwinding of DNA at the origin
+ Helicase (Dna B/Dna С) hydrolyzes ATP and unwinds the DNA double helix
+ Topoisomerases I, II catalyze removal of supercoils forming by helicase
+ SSB-proteins bind to ssDNA and prevent the DNA double helix formation

17. Prokaryotic DNA polymerases
DNA polymerase I
polymerase
3’-exonuclease
5’-exonuclease
DNA polymerase III (the main enzyme of replication)
Structure of DNA pol III:
2 two cores (one for each strand) responsible for the polymerization activity
2 clamps prevent the core enzyme from falling off the template during polymerization
2 subunits which dimerize two cores
Clamp loader complex
DNA polymerases II, IV и V are involved in DNA repair.

18. Properties of DNA polymerases
DNA polymerases catalyze the template-directed polymerization of nucleotides (the formation of a phosphodiester bond)
(dNMP)n + dNTP → (dNMP)n+1 + PP
they are not able to initiate DNA synthesis de novo by catalyzing the polymerization of free dNTPs. They require a primer.
all polymerases synthesize DNA only in the 5′ to 3′ direction.

19. DNA replication enzymes (elongation)
Primase is a specific type of RNA polymerase which creates an RNA primer.
DNA polymerase III synthesizes the leading strand and Okazaki fragments.
DNA polymerase I removes primers and replaces them with deoxyribonucleotides.
DNA ligase joins Okazaki fragments together by catalyzing the formation of a phosphodiester bond.

20. Peculiarities of eukaryotic replication
DNA polymerases:
DNA pol  creates RNA primers. Its processivity is low.
DNA pol β is involved in DNA repair.
DNA pol δ synthesizes the leading strand and Okazaki fragments.
DNA pol ε participates in synthesis of the lagging strand.
DNA pol ζ is involved in DNA repair.
DNA pol γ synthesizes mitochondrial DNA.

21. Peculiarities of eukaryotic replication
Eukaryotic chromosomes contain multiple replication origins.
The Okazaki fragments are about ten times smaller (100 to 150 nucleotides) than in prokaryotes.
Speed of replication is about 50 nucleotides per second (the speed in prokaryotic cells is nucleotides per second).
Primers are removed by RNase Н.
Replication occurs during S phase of the cell cycle.
The end replication problem is handled by telomere regions and telomerase.

22. Telomeres
Telomeres are ends of linear chromosomes which consist of repetitive nucleotide sequences (TTAGGG).
Telomeres shorten with each cell division

23. Telomerase prevents telomere shortening.
Telomerase is an enzyme that adds DNA sequence repeats (TTAGGG) to the 3' end of DNA strands in the telomere regions. (Olovnikov А.М., 1971; К. Greider, E. Blackburn, 1985).
It is a ribonucleoprotein and consists of RNA (451 nucleotides) and reverse transcriptase.
Telomerase prevents telomere shortening.

24. Modes of replication θ-mode 2. σ-mode (rolling-circle replication)
3. Replication of linear molecules