mitotic chromatin

1. P R E S E N T E D B Y : -
S Y E D A T A M A N N A Y A S M I N
M . S C . M I C R O B I O L O G Y 1 S T S E M E S T E R
R O L L : D U 2 0 1 7 M S C 0 1 3 0
MITOTIC
CHROMATIN

2. What is chromatin???
• DNA + Histone = Chromatin
• Chromatin is a complex of macromolecules
found in cells consisting of DNA, protein
and RNA. The primary protein components
of chromatin are histones that compact the
DNA.
• Chromatin is only found in eukaryotic cells.

3. Functions of chromatin
To package DNA.
To reinforce the DNA
macromolecules to allow mitosis.
To prevent DNA damage.
To control gene expression and
DNA replication.

4. Structure of chromatin

5. Types of chromatin
There are two basic types ofchromatins:
 Euchromatin is the genetically active type
of chromatin involved in transcribing RNA to
produce proteins used in cell function and
growth.
 Heterochromatin is the tightly packed
form of DNA. The additional compression of
heterochromatin is thought to involve various
proteins in addition to the histones.

7. Mitotic chromatin
 Mitotic chromosomes represent tightly packed,
transcriptionally repressed chromatin, those are
known as mitotic chromatin.
 They are characteristically resistant to nuclease
accessibility. However, some regions of mitotic
chromosomes remain sensitive to nuclease activity
indicating that some genes remain in open
chromatin conformation, thus giving rise to the
concept of gene bookmarking.

8. Structure of mitotic chromosome

9. Chromatin undergoes profound changes
during mitosis
 In interphase, chromatin is decondensed and nuclear
proteins are confined within the nuclear envelope. Other
factors are associated with chromatin and impart different
chromatin marks.
 During metaphase, the chromatin reaches maximum
condensation and becomes ~300-fold more condensed.
This leads to changes in chromatin volume.
 During mitosis, profound changes in DNA and chromatin
components occur. Chromatin compaction causes
topological stress, which leads to a tenfold increase in the
occurrence of single-stranded DNA.

10. EXAMPLE
Chromatin behavior during the mitotic cell cycle of
Saccharomyces cerevisiae.
• Chromatin is dispersed during interphase and occupies
the non-nucleolar Region.
• However, chromatin was not attached directly to the
spindle pole bodies .
• During nuclear division chromatin remains dispersed
and does not condense into discrete chromatins.
• As the nucleus expands into the bud, chromosomal
distribution to the daughter cells is thought to result
from the separation of the poles of the spindle apparatus
with attached chromatin fibrils.

11. • However, that such distribution is occurring as the
nucleus elongates is not obvious until an advanced
stage of nuclear division is reached and partition of
the nucleus is nearly complete.
• Thus, no aggregation of chromatin into metaphase or
anaphase plates occurs and the appearance of
chromatin during mitosis is essentially the same as
in interphase .
• These observations indicate that the marked changes
in the topological structure of chromatin which
characterize mitosis in the higher eukaryotes do not
occur in S. cerevisiae.