The expression
"chromosome condensation" refers to one of the oldest
recorded phenomena of the chromosome cycle in eukaryotic
cells - the cytological manifestation of chromosomes
themselves. In the most common sense the term refers to
the shortening of the chromosome axis accompanied by
contraction of the chromosome radius. This process inevitably
results in diminished chromosome volume, as
revealed by low-resolution methods (e.g. optical microscopy)
and in reduction of the exposed chromatin surface,
as seen in biochemical tests (e.g. chemical cross-linker or
nuclease accessibility). As DNA in most eukaryotic cells is
already very tightly packed into nucleosomal arrays, the
essence of condensation is likely not in the increasing density
of chromatin fiber itself, but in the folding of this fiber
in a specific manner. It is presently unclear whether
chromosome condensation in eukaryotes results in any
massive physicochemical chromatin alterations, as only a
limited set of physical characteristics has been determined
for condensed chromosomes . Thus, the term
'condensation' does not convey the full meaning of the
biological process it applies to, and should be viewed as a
simplification based on low-resolution methods of
chromosome analysis.
Despite its seemingly superficial nature, i.e. mere
refolding of chromatin fibers, chromosome condensation
is a remarkably ubiquitous process in eukaryotic cells.
Such widespread prominence of chromosome condensation
in the cell cycle led to the suspicion that its role goes
somewhat beyond the task of just making chromosomes
smaller. At the present level of knowledge, chromosome
condensation can be unequivocally classified as an
essential housekeeping function, indispensable for cell
proliferation. Therefore, chromosome condensation is a
potential target for therapeutic agents targeting cell cycle
progression.
The essential nature of chromosome condensation
has not been proven until very recently, yet this direction
of thought was based on the classic topoisomerase II
(TOPOII) study (6). Namely, TOPOII dysfunction in fission
yeast cells was shown to disrupt both chromosome
condensation and progression through anaphase.
Even though the link between the two processes was not
necessarily causal, TOPOII was known to participate in
other functions in chromatin (transcription and replication)
and the TOPOII role in chromosome condensation
turned out not to be universal, the correlation was
rather strong prompting to search for other, possibly more
specialized molecules participating in mitotic chromosome
refolding.
Chromosomes
condense beforemitosis
to allow them the ability to move smoothly, without becoming entangled and breaking. (So, they are conveniently packaged forcell
division
, in which the chromosomes must move to both poles of the cell.)
The chromosomes duplicate at the end of interphase making the cell 4N and the pachytene phase (this may be an old-fangled term) is where the chromosomes condense into discrete components so that they can "line up" for division into 2, 2N cells. Think of it as a way of organizing a pile of different colored strings into discrete units so that 1 string of each kind ends up in a different pile. If condensation didn't occur the separation would be extremely difficult.
At the onset of mitosis, the chromatin coils and condenses to form chromosomes. This occurs during the prophase stage of mitosis.
They Condense because the DNA wraps around proteins that help organize
So DNA does not get tangled or broken.
a stage during mitosis consisiting of the regrouping of chromatides and string like chromosomes. In summery Chromosomes uncoil and revert to chromatin; nuclear membranes form around the sets of chromosomes.
Mitosis
The nuclear membrane reforms around the nucleus during Telophase, the last phase of mitosis.
first it becomes two chromatids, then during prophase, chromosomes condense from long strands into rod like structures. During METAPHASE paired chromatids align at the cell's equation. Then during ANAPHASE the paired chromatids separate and move to the opposite side of the cell. During TELOPHASE a nuclear membrane forms around each set of chromosomes, and the chromosomes decondense.
During the first stage of mitosis, prophase, the nucleus and nucleolus disappear. Mitosis then proceeds into metaphase and anaphase. Then during telophase, the nuclei reappear in the two cells and finally the cells split apart from each other by a process known as cytokinesis.
a stage during mitosis consisiting of the regrouping of chromatides and string like chromosomes. In summery Chromosomes uncoil and revert to chromatin; nuclear membranes form around the sets of chromosomes.
during metaphase and anaphase
a stage during mitosis consisiting of the regrouping of chromatides and string like chromosomes. In summery Chromosomes uncoil and revert to chromatin; nuclear membranes form around the sets of chromosomes.
a stage during mitosis consisiting of the regrouping of chromatides and string like chromosomes. In summery Chromosomes uncoil and revert to chromatin; nuclear membranes form around the sets of chromosomes.
DNA wraps around proteins that help organize and condense it.
Phase 1- Mitosis begins. Chromosomes condense from long strands into rodlike structures. Phase 2- The nuclear membrane is dissolved. Paired chromatids align at the cell's equator. Phase 3- The paired chromatids separate and move to opposite sides of the cell. Phase 4- A nuclear membrane forms around each set of chromosomes, and the chromosomes decondense. Mitosis is complete.
Mitosis
The nuclear membrane reforms around the nucleus during Telophase, the last phase of mitosis.
It organizes the microtubules in mitosis. The microtubules move the chromosomes around the cell during mitosis, most importantly lining the chromosomes up at the metaphase plate in metaphase so that they can split up into the two daughter cells.
first it becomes two chromatids, then during prophase, chromosomes condense from long strands into rod like structures. During METAPHASE paired chromatids align at the cell's equation. Then during ANAPHASE the paired chromatids separate and move to the opposite side of the cell. During TELOPHASE a nuclear membrane forms around each set of chromosomes, and the chromosomes decondense.
During the first stage of mitosis, prophase, the nucleus and nucleolus disappear. Mitosis then proceeds into metaphase and anaphase. Then during telophase, the nuclei reappear in the two cells and finally the cells split apart from each other by a process known as cytokinesis.
Histone proteins