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stem cells are pluripotent cells which are found in the inner cell mass of
blastocyst-stage embryos. These are maintained and in culture up until the time
they are needed.When
the embryonic stem cells are in culture, they must be grown under suitable
conditions in order for them to remain undifferentiated. However if they clump
together they will form embryoid bodies.They
begin to differentiate unexpectedly. This means they can form muscle and nerve
cells. Impulsive differentiation suggests that the culture of embryonic stem
cells is healthy. This process enables the generation of specific types of
differentiated cells like heart muscle cells and blood cells. Nonetheless, to
make these cultures scientists attempt to control the differentiation of stem
cells by changing the chemical composition of the culture medium and alter the
surface of the culture dish. They can also interrupt the differentiation
process by modifying the cells by inserting specific genes.

Cell division does not take place by
random chance. The cell divides according to the conditions in its environment
and genetic code. Cells receive extracellular chemical signals from the body or
other cells that will cause them to start dividing. These chemical signals are
known as mitogens. In addition, other cells can release chemical substances
which will cause nearby cells to divide. One of these is cytokines. Cytokines
are a type of signaling molecule and are mainly used for intercellular
communication. These are molecules which are produced in cells of the immune
system and also in the nervous system. Cells can also be induced into
dividing due to growth factors. The surface of the cell membrane has different
receptor regions for specific regulatory proteins. When the receptor region is
filled with the protein it then sends a signal that activates proteins within
the cell and results in cell division to begin.

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cell cycle is not a linear pathway because in the end the two daughter cells
can start the same process again from the beginning.Interphone is very first the stage where the
cell grows and makes a copy of its DNA. Then leading to the mitotic phase where
the cell will separate the DNA into two copies, dividing the cytoplasm forming
two daughter cells. The process of interphase has three phases. The first phase
is called the G1 (growth phase) which is the longest phase. The cell grows larger as in double its size and copies
organelles. Here is where the cytoplasm increases in volume. It also produces molecular
building blocks for the next two phases. ATP is synthesised to provide energy
for replication. Finally the cell will remain in this phase if the cell is not
going to divide. In the second phase which is known as the S phase where
synthesis occurs to create sister chromatids.The cell duplicates by the process
of semi conservative replication. Semi conservative replication is when a double stranded DNA molecule separates and each strand
is used as a template for the synthesis of a new strand. Producing two
identical copies of the original double stranded molecule. The third phase is G2
(growth 2) is a short gap before mitosis in which the cell resumes its growth by making more
proteins and organelles in preparation for mitosis. Also the cytoskeleton of
the cell breaks down and the protein microtubule components begin to reassemble
into spindle fibres.

Mitosis is a form of cell
division where a cell divides to generate two daughter cells which are
genetically identical to that same cell. The purpose of mitosis is to grow and
repair damaged a cell, that’s how wounds heal. There are four significant
phases firstly, to begin with prophase. In prophase, chromosomes condense and
become visible. The chromosomes coil becoming shorter and fatter. The nucleolus
disappears and the nuclear envelope breaks down. The centrioles move to
opposite poles of the cell. Each centriole forms spindle fibers. The mitotic
spindle forms it’s made of strong fibers called microtubules. The spindle
organises the chromosomes and moves them around when necessary. Next, in
metaphase one or more spindle fibres attach to the centromere of each
chromosome. The chromosomes are then pulled along the spindle apparatus and
arrange themselves across the equator of the cell. Anaphase is the third phase
of mitosis where the centromeres divide into two and spindle fibres shorten,
pull and contract one of each pair of sister chromatids to opposite poles of
the cell. Now each pole will have the exact same number and type of chromosomes.
The chromatids will now be called chromosomes. Also the energy fro this process
is provided by the mitochondria during aerobic respiration. The last stage of
mitosis is telophase where the
cell is almost towards the finish line of dividing, and it starts to reform its
normal structures as cytokinesis occurs. The spindle is broken down. Then two
new nuclei form with the nuclear membranes and nucleoli reappearing. And
eventually chromosomes decondense and return to their original form. Just to finish
the whole process of cytokinesis, the cytoplasm
divides into two and we have two new cells, each with a complete set of
chromosomes identical to those of the original cell we started with.

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