Multicellular organisms rely on cell division for growth and the replacement of lost cells, with somatic cells generated through a controlled sequence known as the cell cycle, comprising notable phases: interphase and mitotic (M) phase. Interphase involves cell growth and DNA synthesis across distinct G0, G1, S, and G2 stages, while mitosis is a rapid process divided into five phases culminating in the formation of two identical daughter cells. The document details how these processes function and regulate cellular activity, leading to proper division and the generation of new cells.

2. Multicellular organisms are composed of a variety of specialized cells organized
into a cellular community. When an organism requires additional cells, either for
growth or to replace those normally lost, new ones must be produced by cell division,
or proliferation. Somatic cells are generated by the division of existing cells in an
orderly sequence of events. They duplicate their contents and then divide to produce
two identical daughter cells. This sequence of duplication is known as the cell cycle
and is the essential mechanism of eukaryotic reproduction. Cell division occurs
throughout the life of the organism, although different cell types divide more or less
often than others. Cells display remarkable variation in their proliferative capacity,
depending on the cell type and the age of the individual.
the new cell originate only from other living cells, the process by which this
occurs is called cell division.

3. each cell passes through a series of defined stages. Which
constitutes the cell cycle can be divided into two major phases based on
cellular activity which are readily visible with the light microscope.
1. interphase
2. M- Phase

4. all cells, whether actively cycling or not, spend the vast of their lives in interphase is
an eventful and important part of the cell cycle and comprises G0, G1, S, and G2 phases,
cellular growth and DNA synthesis occur during interphase, resulting in a duplication of
cellular materials so that there are sufficient materials for two complete new daughter cell.

5.  named for the gap that follows mitosis and the next round of DNA synthesis
 G1 phase is generally both a growth phase & preparation time for DNA synthesis of S
phase
 RNA and protein also synthesized in this phase in addition organelles and
intracellular structure are duplicated and the cells grows during this phase
 the length of G1 phase is variable among cell types. Very rapidly cells, such as
growing embryonic cell
 these cells in G1 phase that are not committed to DNA synthesis are in a specialized
resting state called G0 phase. Some inactive or quiescent cells in G0 phase may
reenter the active phase of cell cycle upon proper stimulation.
 the restriction point is critical for cell cycle regulation is located with in G1 phase and
if passed with commit a cell to continuing into DNA synthesis within S phase

6.  occur the DNA replication
 46 chromosomes in a human cells is copied to form a sister chromatid
 ATP- depended unwinding of chromatin structure by DNA helicase exposes the binding
sites of for DNA polymerase that will catalyze the synthesis of new DNA in the 5’ to 3’
direction

7.  multiple replication forks are activated on each chromosome & entire genome is
duplicated within the time span of S phase
 after this chromosome synthesis this strands are condensed into tightly coiled
heterochromatin
 time of preparation for the nuclear division of mitosis
 this safety gap allows the cell to ensure that DNA synthesis is complete before
proceeding to nuclear division in mitosis

8.  G2 is a check point where intracellular regulatory molecules asses nuclear integrity
mitosis or nuclear division is a continuous process and can be divided into five phase
based on progress made to a specific point in the overall nuclear division
 that occur in 1 hour in mitosis
 after completion division resulting in the formation of two sepate daughter cells
from the on parent cell

9. .

10.  in prophase the nuclear envelop remains intact while the chromatin that was
duplicated during S phase condenses into defined chromosomal structures called
chromatids.
 chromosomes of mitotic cells contain two chromatids connected to each other at a
centromere
 specialized protein complexes, called KINETOCHORES, form and associate with each
chromatid.
 mitotic spindle microtubules will attach each kinetochore as chromosomes are moved
apart later in mitosis
 the microtubules of the cytoplasm disassemble and then reorganize on the surface of
the nucleus to form the mitotic spindle. Two centriole pairs push away from each other
by growing bandles of microtubules forming the mitotic spindle. The nucleolus, the
organelle within the nucleus where ribosomes are made, disassembles in prophase.

11.  chromosomal microtubules attach to kinetochores of chromosomes
 chromosomes are moved to spindle equator

12. • z
Astral
microtubules
Centrosome

13.  chromatids aligned at the equator of the spindle, halfway between the two poles
 the aligned chromatids form the metaphase plate cells be arrested in metaphase
when microtubule inhibitors are used
 karyotype analyses used to determine the over all chromosome composition and
structure most often require cells in metaphase.

14.  the mitotic poles are pushed further apart as a result of polar microtubules
elongation
 each centromere splits in two and paired kinetochores also separate. Sister
chromatids migrate toward the opposite poles of the spindle

15.  the last phase of nuclear division, telophase is characterized by kinetochore
microtubule disambly and mitotic spindle dissociation
 chromosomes become dispersed
 nuclear envelope assembles around chromosomes clusters
 golgi complex and ER reforms
 daughter cells formed by cytokinesis

16.  in order to create two distinct, separate daughter cells. Cytoplasmic division follows
nuclear division
 an actin microfilament ring forms to crate the machinery needed. Contraction of this
actin based structure results in the formation of a cleavage furrow.
 the furrow deepens until opposing edges meet. Plasma membrane fuse on each side
of the deep cleavage furrow and the result is the formation of two separate daughter
cells, each identical to the other and to the original parent cell

18. • REFERENCE:
 Gerald Karp - Cell and Molecular Biology_ Concepts and Experiments-Wiley (2010), 1ST edition
188-195.
 (Lippincott’s Illustrated Reviews) Nalini Chandar, Susan Viselli - Cell and Molecular Biology
(Lippincott’s Illustrated Reviews) -Lippincott Williams & Wilkins (2010), 6th edition, 569-588.