Cell cyle and dvision Flashcards
What is the ceell cycle
cycle of events involving the production of duaghter cells from a parent cell by following correct processes in a coordinated manner whcih includes:
- duplication of genome
-synthesis of additional consitituents
-division of cell i
does dna replication occur along with celll growth
Although cell growth (in terms of cytoplasmic increase)
is a continuous process, DNA synthesis occurs only during one specific
stage in the cell cycle. The replicated chromosomes (DNA) are then
distributed to daughter nuclei by a complex series of events during cell
division. These events are themselves under genetic control.
what are two phases of the cell cycle
interphase
- resting phase
-preparatory phase
-phase between two successive m-phases
mphase or mitotic phase:
- dividing phase
-actual karyokinesiss and cytokinesis takes place her
what is the time taken by a human cell to divide?
The human cell takes an avoerage of 24 hours to divide. Of this time only 1 hour is spent in the M-phase. 95% of the time is spent in the Interphase.
The yeast cell takes 90 mins to divide
what is the interphase?
The interphase, though called
the resting phase, is the time during which the cell is preparing for division
by undergoing both cell growth and DNA replication in an orderly manner.
The interphase is divided into three further phases:
l G1
phase (Gap 1)
l S phase (Synthesis)
l G2
phase (Gap 2)
What is done in the G1 phase
G1
phase corresponds to the interval between mitosis and initiation
of DNA replication. During G1 phase the cell is metabolically active and
continuously grows in cytoplasmic area.
protein and rna syntheisis
organelle duplication
what is done in the S phase
S or synthesis phase
marks the period during which DNA synthesis or replication takes place.
During this time the amount of DNA per cell doubles. If the initial amount
of DNA is denoted as 2C then it increases to 4C. However, there is no
increase in the chromosome number; if the cell had diploid or 2n number
of chromosomes at G1
, even after S phase the number of chromosomes
remains the same, i.e., 2n.
In animal cells, during the S phase, DNA replication begins in the
nucleus, and the centriole duplicates in the cytoplasm.
synthesis of histone
what is done in the G2 phas
During the G2
phase, proteins are synthesised in preparation for mitosis while cell growth
continues.
tubulin for spindle fibres
final preparation for cell division
what is G0 or quiscent stage
Some cells in the adult animals do not appear to exhibit division (e.g.,
heart cells) and many other cells divide only occasionally, as needed to
replace cells that have been lost because of injury or cell death. These
cells that do not divide further exit G1
phase to enter an inactive stage
called quiescent stage (G0
) of the cell cycle. Cells in this stage remain
metabolically active but no longer proliferate unless called on to do so
depending on the requirement of the organism.
cna haploid mitosis take place
In animals, mitotic cell division is only seen in the diploid somatic
cells. However, there are few exceptions to this where haploid cells divide
by mitosis, for example, male honey bees. Against this, the plants can
show mitotic divisions in both haploid and diploid cells.
why is mitosis called equational division?
Since the number of
chromosomes in the parent and progeny cells is the same, it is also called as
equational division. Though for convenience mitosis has been divided
into four stages of nuclear division (karyokinesis), it is very essential to
understand that cell division is a progressive process and very clear-cut
lines cannot be drawn between various stages.
what is the 1st phase of mitsosis
It is the first stage of karyokinesis in mitosis.
- Chromosomal material condenses to form compact mitotic
chromosomes. Chromosomes are seen to be composed of two
chromatids attached together at the centromere. - Centrosome which had undergone duplication during interphase,
begins to move towards opposite poles of the cell. Each centrosome
radiates out microtubules called asters. The two asters together
with spindle fibres forms mitotic apparatus. - The nuclear envelope, nucleolus, ER and Golgi bodies disintegreate to initiate the formation of mitotic spindle
what is the metaphase
- completion of condenstaion of compact chromosomes. This is the best stage for the study of morphology of the chromosome.
- The kinetochores (on centromere of chromosomes) serve as the site of attachment of the spindle fibres to the chromosomes that get aligned along the equator of the spindle apparatus. This equitorial plane is also called as Metaphase plate.
the metaphase is characterised by all the
chromosomes coming to lie at the equator with one chromatid
of each chromosome connected by its kinetochore to spindle
fibres from one pole and its sister chromatid connected by
its kinetochore to spindle fibres from the opposite pole
what happens in anaphase
- The contraction of the spindle fibres results in the splitting of the centromere and hence the chromosomes gets divided into daughter chromatids, also called the daughter chromosomes of future daughter nuclei.
- The chromatids now migrate towards the poles
- The movement of chromatids is such that the centromere is facing towards the pole and is the leading edge while the arms are trailing behind
what happens in telophase
Telophase is the reversal of prophase
* The chromosomes cluster at theopposite spindle poles and they begin to decondense and lose their identitiy as discrete elements. They form a cluster of chromatin material.
* Nuclear envelope developes around the cluster of chromosomes at each pole forming two duaghter nuclei.
* ER, golgi complex and nucleolus reform.
