topic three - cell division, diversity and organisation - miss whitehouse Flashcards
what happens in the cell cycle and how long does it take?
the cell cycle describes the events that take place
as one parent cell divides to produce two new
daughter cells
it takes around 24hours in a human cells
what is a eukaryotic cell cycle made up of?
m - mitosis and cytokinesis 1 hour
I - Interphase the period between divisions when DNA is replicated and the cell prepares for division. Lots of
respiration occurs to produce ATP 23 hours
what happens in gap 1 - cell cycle
synthesis of new organelles and proteins, increase in cell volume 10 hours
what happens in gap 2 - cell cycle
volume of cell increases, proteins needed for mitosis are synthesised 4 hours
state the roles checkpoints include?
helping to prevent uncontrolled division which may lead to tumours
detecting and repairing DNA damage (e.g. from
radiation/sun exposure)
ensuring that DNA is only replicated once per cycle and that the cycle cannot move backwards
what does p53 gene trigger?
the p53 gene triggers the two main cell cycle checkpoints and is known as a tumour suppression gene as it ensures cell division is regulate
review the checkpoint sheets?
in book
state the five facts about mitosis?
necessary for growth and repair of tissues (replacement of cells) number of chromosomes stays the same 1 division results in genetically identical cells produces diploid cells asexual reproduction 2 daughter cells formed
state there five facts about meiosis?
takes place in the reproductive organs to produce gametes
number of chromosomes is halved
2 divisions
results in genetically different (unique) cells
produces haploid cells
sexual reproduction
4 daughter cells formed
define haploid?
a cell or organism that has one copy of each chromosome/one set of
chromosomes (e.g. gametes)
define diploid?
cells or organisms that have two
copies of each chromosome in their nuclei
(e.g. normal somatic (body) cells)
define gametes?
sex cells (sperm and ova in animals, pollen and ova in plants)
why does mitosis take place?
for growth and replacing damaged cells/repairing tissue
state the four things that happen in mitosis?
original “parent” cell chromosomes are copied and double in number chromosomes are divided 2 daughter cells, genetically identical to the original “parent” cell
what are homologous chromosomes?
chromosomes in matching
pairs that hold the same genes at the same positions
along the chromosome
define histone?
a protein that
DNA is wrapped around
to form chromatin (found
in the cell nucleus)
define chromatids?
the
“arms” of a replicated
chromosome
define centromere?
the area of a chromosome where two sister chromatids are joined together Chromatids – the “arms” of a replicated chromosome During cell division the chromatin coils up (condenses) to for
what happens to the chromatin during cell division?
chromatin coils up (condenses) to form
visible chromosomes which can be seen under a light microscope
Chromatin thread = 30nm thick; chromosome = 500nm thick
what are the four stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
define prophase in the cell cycle?
longest stage
chromosomes shorten and thicken by
supercoiling (condensing) to form sister
chromatids. The chromosomes are now
visible
the nuclear envelope breaks down
the centriole divides in two (animal cells
only) and the two centrioles move to
opposite poles of the cell
spindle fibres are formed between the
two centrioles from a cytoskeleton
protein called tubulin (in plants the
tubulin forms from the cytoplasm
define the metaphase stage?
short stage
chromosomes move to the equator of the
cell (centre of the spindle fibres)
chromosomes attach to the spindle by their
centromeres
define the anaphase stage?
short stage
centromere splits
the spindle shortens, pulling sister
chromatids in opposite directions towards
the poles of the cell (involves cytoskeleton)
define the telophase?
chromatids reach the poles of the cell
new nuclear envelope forms around each set
spindle breaks down
chromosomes uncoil and become invisible
again
when does cytokinesis occur?
after mitosis
what does cytokinesis do in animal cells?
in animal cells, cytokinesis starts from the outside – ‘nipping in’ the cell membrane and cytoplasm along what is termed a cleavage
furrow
what does cytokinesis do in yeast cells?
in yeast cells, cytokinesis produces a small bud that nips off the parent cell (budding)
what does cytokinesis do in plant cells?
in plant cells cytokinesis starts with the formation of a cell
plate where the spindle equator was.
Vesicles (containing carbohydrates e.g. pectin) produced by the Golgi body line up along the equator 2. Vesicles fuse to form a cell plate 3. The cell plate stretches across the cell, forming the middle lamella 4. Cellulose builds up on each side to form the cell walls of the two new cells
what are meristems?
is the tissue in most plants containing
undifferentiated cells, found in zones of the plant where
growth can take place
where does mitosis occur in plants?
mitosis only occurs
in shoot and root tips where meristem cells are found (zones of active cell division)
what is meiosis?
meiosis is cell division which produces four daughter cells, each with half the original number of
chromosomes
where does meiosis take place?
in the reproductive organs to form haploid gametes
what are the two separate divisions in meiosis?
meiosis I - genetic variation is introduced through
crossing over and independent assortment
meiosis II - chromosomes (pairs of chromatids)
are split and four haploid cells are produced
how many stages does each division have and what are these stages?
four stages - prophase, metaphase, anaphase, telophase
state three reasons why meiosis is important?
it produces haploid gametes
this ensures that when gametes fuse together at
fertilisation the resulting zygote is diploid. Without
meiosis the chromosome number would double in
successive generations
it also contributes to genetic variation, which allows
evolution through natural selection to take place
reasons how meiosis increases genetic variation?
crossing over (in prophase I) reassortment of chromosomes (in metaphase) reassortment of chromatids (in metaphase II) random mutations