Molecular base of
Inheritance DNA
Premedical - biology
Proof that DNA is carrier of
genetic information - 1928
•
Griffith‘s experiment - Bacterial transformation
•
Recombination of bacterial genetic material by
transmission of naked DNA into recipient cells
•
Avery, McLeod, McCarthy (1944) – the same effect
with isolated DNA
Streptococcus pneumonie – S strain and R strain
1953 - James D. Watson a Francis Crick
used x-ray diffraction data collected by Rosalind Franklin
•
proposed the double helix as the threedimensional
structure of DNA
•
the main role is the long-term storage of information
•
ability to manage its own replication
•
DNA manage the development of biochemical, anatomical
and physiological and behavioral traits of all known living
organism
Monomers - nucleotides: organic molecule called a
nitrogenous base, a pentose (five-carbon sugar) and
phosphate group
Two families of nitrogenous bases: pyrimidines, purines

into a new complementary strand
= Semiconservative replication
Cell cycle
Replication
Origins of replication
•
circular bacterial chromosome has a single origin
•
Replication starts in many places (Eukaryotes)
simultaneously and asynchronnous
•
DNA replication proceeds in both direction
•
At each end of replication bubble is replication fork
•
DNA polymerase – addition of nucleotides only to the
free 3‘ end, new strand can elongate only in one direction
(5´→ 3´) + and correction of mistakes
A new strand in direction 5´→ 3´ leading strand
The other strand – lagging s. is synthetized
discontinuously - Series of segments = Okazaki fragments
enzyme DNA Ligase joins them
Primase -
RNA primers
Helicase
•
One /10 000bp in replication
•
DNA polymerase
•

•
Histones – basic proteins
H1,H2A, H2B,H3,H4
• Non-histone proteins
The whole length DNA cca 2 m
human genome contains cca 30 000
structural genes
Ultrastructure of chromosomes
Nucleosome:
DNA double helix + histone core
•
Histone core = octameres of two copies of H2A,
H2B, H3, H4
•
DNA double helix is winded around the core
•
spacer segment DNA between two nucleosomes is
free or associated with H1 histone (appearance of
beads on a string)
Organization of chromatin in interphase


Condensation of chromatin into chromosomes
•
String of nucleosomes is coiled into
solenoid (6 nucleosomes in each
turn)
•
Solenoid is packed into loops attached
to the nonhistone protein scaffold

reduction of number of telomeres after each
replication
•
abnormal activity of telomerase in tumor cells