Chromosomes and mitosis

chromsome structure, different stages of mitosis

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  • Created by: malu
  • Created on: 04-07-13 10:52
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DNA AND CHROMOSOMES
Differences in DNA
Prokaryotic cells Eukaryotic cells
No true nucleus True nucleus
No chromosomes DNA combines with proteins to form
Circular DNA chromosomes located inside the
No associated proteins nucleus
Chromosome structure
Chromosomes are only visible as distinct structures when a cell is dividing.
Chromosomes appear as two threads,
joined at a single point. Each thread is
called a CHROMATID.
DNA in chromosome is held together
in place by proteins (histones). DNA
is highly coiled and folded. The coil is then
looped and further coiled before being
packed into the chromosome.
Chromosomes are made up of;
DNA (about 27%)
Proteins mainly bead like histones (about 67%)
RNA (about 6%)
Histones and DNA bind together to form a bead like stable structure called Chromatin
Chromatin =
DNA + proteins
The number of
chromosomes is
always the same
for normal
individuals of a
species, but it
varies from one
species to
another.

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The chromosome number for a given species is always constant. In the nucleus of
the somatic (body) cells in eukaryotes the chromosomes occur in homologous
pairs ­ the cells are DIPLOID (2n/ in pairs)
Gametes are HAPLOID ­they contain HALF the normal number of chromosomes
(e.g. sperm and egg)
The compact `X' like structure is not apparent until the chromosomes condense
during mitosis or meiosis. At metaphase each chromosome is seen to consist of
two sister chromatids joined together at the centromere.…read more

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Mitosis is the division of the nucleus of a cell that results in each of the daughter
cells having an exact copy of the DNA of the parent cell except the rare event of
mutation.
Mitosis is involed in:
· GROWTH ­ an increase in size through the division of cells and development of
a multicellular organism from a single fertilised egg
· CELL REPLACEMENT ­ many cells are constantly dying and being replaced eg.…read more

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The cell cycle
Three stages of cell cycle:
INTERPHASE- which occupies most of the cell cycle.…read more

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Cancer is a group of diseases caused by growth disorder of cells. It
is caused by damage to the genes which regulates mitosis and the
cell cycle.
Cancer treatment
Cancer is treated by blocking the cell cycle to prevent the uncontrolled cell
division.
Chemotherapy involves drugs which disrupts cell cycle:
Preventing DNA from replicating
Interfering with spindle formation and so inhibiting metaphase
Meiosis
Meiosis is a type of cell division used in sexual reproduction to produce gametes.…read more

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