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Cell Division and the Cell Cycle
The Cell Cycle
Interphase is made of 3 other smaller phases.
G1 Phase: proteins for cell organelles are synthesised and
produced. Volume of cytoplasm increases, new organelles
S Phase: DNA replication Centrioles are also replicated in this phase
one of the few organelles to do so. They come in pairs.
G2 Phase: Organelles grow and divide, and energy stores
are increased. Makes the specific enzymes and other
proteins needed to complete M.
M Phase: Prophase: Chromatin threads
condense to form chromosomes,
with their chromatids fully
formed, and joined at the
centromere. Spindle fibres form.
Centrioles appear at opposite
poles. Nucleolus and nuclear
Metaphase: The chromosomes
arrange themselves at the
equator of the cell. As the
nuclear envelope broke down
it disassociates into
vesicles which are
from the ER. The chromosomes
become attached to the
Anaphase: Each chromatid
migrates to an opposite pole, as
spindle fibres shorten and
Telophase: Nuclear envelope reforms. Spindle disintegrates, nuclear
envelope and nucleolous reform, chromosomes become undistinguishable.
Mitosis produces 2 new daughter nuclei, with the same number of chromosomes as the
parent cell, and each other they must have identical DNA. It's always preceded by a
period of non-cell division, known as interphase, which is where a significant amount of
intracellular activity takes place. Mitosis is a continuous process. It's important in:
Growth: If a organism is to grow from a zygote, it must possess the same
genetic information to divide and give a set of identical cells.
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Differentiation: Cells must differentiate in order to give specialised cells,
dividing by mitosis to give tissues of identical cells. Tissues can only be
efficient if all it's cells have the same structure/function.
Repair: New cells produced to replace old ones must have an identical
structure and function, to ensure that tissues function as effectively.
Cytoplasmic Division: divides by cleavage. The plasma membrane around the middle of
the cell is drawn inwards to form a cleavage furrow, gradually deepening till 2 cells
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They non-sister chromatids break
and re-join: equal amounts of the chromatid being exchanged between one chromosome
and another, increasing the genetic variety.
Cancers are a result of uncontrolled cell growth. Mutations occur in the DNA of a cell,
causing it to divide unnecessarily, till a mass of cancerous cells result into a tumour.
Chemicals Industrial chemicals are found to be carcinogenic, including those found in
cigarettes. High fat and low fibre diet also appears to effect our susceptibility to bowel
cancer in particular.…read more