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The cell will also replicate its
centrosome, which is important for
movement of chromosomes
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During this time, the
cytoplasm is still active, and the cell
continues with its normal
functions, such as protein synthesis, mitochondria replication or chloroplast
replication
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S is the synthesis phase when the DNA is replicated
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All the chromosomes are copied and form chromatids
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G₂ is the third stage, standing for Gap 2, when there is more growth of the cell, then
preparation takes place for cell division
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This consists of four stages: prophase, metaphase, anaphase and
telophase
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Cytokinesis is the division of the cytoplasm to form two daughter cells
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2 - State that tumours (cancers) are the result of uncontrolled cell division and that
these can occur in any organic tissue
Tumours, or cancers, are cell mass formed as a result of uncontrolled cell division
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In a tumour, the normal repressed state of mitosis is disrupted by mutation to the protooncogene
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The proto-oncogene mutates
into the oncogene, resulting in the loss of control of cell division
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Some cells may break away and form a
secondary tumour elsewhere
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It is caused by damage to DNA chromosomes
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Another cause is damage to the
gene that codes for p53, the protein which stops the copying of damaged DNA
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), some
chemicals (tar in tobacco smoke) as well as virus infections
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The development of cancer requires at least two mutations; one of the proto-oncogene;
two of the tumour suppressor
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3 - State that interphase is an active period in the life of a cell when many metabolic
reactions occur, including protein synthesis, DNA replication and an increase in the
number of mitochondria and/or chloroplasts
This is always the longest part of the cell cycle
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The chromosomes disperse as chromatin
and become actively involved in protein synthesis
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Proteins are assembled in the ribosomes by combining
amino acids in sequences dictated by the information from the gene
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There is
intense biochemical activity in the cytoplasm and the organelles, and there is an
accumulation of stored energy before nuclear division occurs again
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These
remain attached until they divide in mitosis
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The length of
interphase varies between cell types
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Then, in the S stage, the DNA is replicated
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Mitochondria (and chloroplasts in plants) are replicated
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Mitosis is a continuous process with no breaks in it, although we divide it into four stages
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They shorten and thicken through
the process of supercoiling
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The genes must be left in

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predictable positions and a distinctive overall chromosome shape
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At the end of prophase, it is possible to see that the two chromatids are held
together at the centromere
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Metaphase
The centrioles move to opposite ends of the cell
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These attach to the centromeres and are arranged at the equator of
the spindle
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Anaphase
The centromeres divide, the spindle fibres shorten, and the chromatids
are pulled by their centromere to opposite poles
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Telophase
The nuclear membrane reforms around both groups of chromosomes
at opposite ends of the cell
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The nucleolus reforms
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5 - Explain how mitosis produces two genetically identical nuclei
Cell division produces genetically identical daughter cells
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An exact copy of each chromosome is made by accurate replication during interphase
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The chromatids remain attached by their centromeres during metaphase, when each
becomes attached to a spindle fibre at the equator of the spindle
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The chromosomes then form two new nuclei when the cell splits
into two, each with an exact copy of the original nucleus
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6 - State that growth, embryonic development, tissue repair and asexual reproduction
involve mitosis
In the growth and development of an embryo, it is very important that all cells carry the
same genetic information as the existing cells from which they are formed, and with which
they share surrounding cells or tissues
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These cells can then
differentiate and specialise their function
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If this was not the
case, different body part would begin working to conflicting blueprints, resulting in chaos
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In other words, they are clones
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