The Cell Cycle

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The Cell Cycle
The mitotic phase can be sub-divided 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
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
This is when the cell is not dividing, but is
carrying out its normal cellular functions.
chromatin not visible
DNA, histones and centrioles all replicated
Replication of cell organelles e.g. mitochondria,
occurs in the cytoplasm.
chromosomes condense and become visible ­
this prevents tangling with other
Due to DNA replication during interphase, each
chromosome consists of two identical sister
chromatids connected at the centromere
centrioles move to opposite poles of cell
nucleolus disappears
phase ends with the breakdown of the nuclear
spindle fibres (microtubules) connect centrioles
to chromosomes
chromosomes align along equator of cell and
attaches to a spindle fibre by its centromere.
centromeres split, allowing chromatids to
chromatids move towards poles, centromeres
Anaphase first, pulled by kinesin (motor) proteins walking
along microtubules (the track)
Numerous mitochondria around the spindle
provide energy for movement

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nucleoli form
In animal cells a ring of actin filaments forms
round the equator of the cell, and 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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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.
Sexual reproduction involves two stages:
Meiosis- the special cell division that makes haploid gametes
Fertilisation- the fusion of two gametes to form a diploid zygote
The Advantages of Sexual Reproduction
For most of the history of life on Earth, organisms have reproduced only by asexual
reproduction.…read more

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Homologous Chromosomes
The chromosomes are numbered from largest to smallest.
Chromosomes come in pairs, called homologous pairs ("same shaped"). So there are
two chromosome number 1s, two chromosome number 2s, etc, and humans really
have 23 pairs of chromosomes.…read more


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