The Cell Cycle, cell division by mitosis, meiosis, DNA and chromosomes and Homologus chromosomes

A detailed document about the cell cycle, division by mitosis & meiosis, DNA and chromosomes

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  • Created on: 11-03-13 19:37
Preview of The Cell Cycle, cell division by mitosis, meiosis, DNA and chromosomes and Homologus chromosomes

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The Cell Cycle
Cells are not static structures, but are created and die. The life of a cell is called the cell
cycle and has four phases:
In different cell types the cell cycle can last from hours to years. For example bacterial
cells can divide every 30 minutes under suitable conditions, skin cells divide about every
12 hours on average, liver cells every 2 years.
The mitotic phase can be subdivided into four phases
(prophase , metaphase, anaphase and telophase ). Mitosis is strictly nuclear division, and is
followed by cytoplasmic division, or cytokinesis, to complete cell division. The growth and
synthesis phases are collectively called interphase (i.e. in between cell division). Mitosis
results in two "daughter cells", which are genetically identical to each other, and is used for
growth and asexual reproduction.
Cell Division by Mitosis
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Mitosis is a type of cell division that produces genetically identical cells. During mitosis
DNA replicates in the parent cell, which divides into two new cells, each containing an
exact copy of the DNA in the parent cell. The only source of genetic variation in the cells
is via mutations.
This is when the cell is not dividing, but is
carrying out its normal cellular functions.
chromatin not visible
Interphase DNA, histones and centrioles all
Replication of cell organelles e.g.…read more

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In animal cells a ring of actin filaments
forms round the equator of the cell, and
Cytokinesis then tightens to form a cleavage furrow ,
which splits the cell in two.
In plant cells vesicles move to the
equator, line up and fuse to form two
membranes called the cell plate. A new
cell wall is laid down between the
membranes, which fuses with the existing
cell wall.…read more

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You don't need to know the details of meiosis at this stage (It's covered in module 5).
Meiosis and Sexual Reproduction
Sexual reproduction is the production of offspring from two parent using gametes . The
cells of the offspring have two sets of chromosomes (one from each parent), so are
diploid.…read more

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During most of the life of a cell the chromatin is dispersed throughout the nucleus and
cannot be seen with a light microscope. At various times parts of the chromatin will unwind
so that genes on the DNA can be transcribed. This allows the proteins that the cell needs
to be made.
Just before cell division the DNA is replicated, and more histone proteins are synthesised,
so there is temporarily twice the normal amount of chromatin.…read more

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This display is called a karyotype, and it shows several features:
Different species have different number of chromosomes, but all members of the
same species have the same number. Humans have 46, chickens have 78,
goldfish have 94, fruit flies have 8, potatoes have 48, and so on. The number of
chromosomes does not appear to be related to the number of genes or amount of
The chromosomes are numbered from largest to smallest.
Chromosomes come in pairs, called homologous pairs ("same shaped").…read more


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