Cell division Flashcards
cells can only be formed from?
existing cells
when a new cell forms it goes through 3 stages before it can divide again. what are they?
synthesis of materials it will need
growth
reproduction to form new cells
the forming of new cells is called
cell continuity
cell continuity can be summarised in
the cell cycle
what does the cell cycle describe
interphase and mitosis
what is interphase
a cell’s state of non-division
what is a state of mitosis
a cell’s state of division
3 stages of the cell cycle
division of nucleus
division of cell
interphase
the long part of the cell cycle
interphase
the short parts of the cell cycle
division of nucleus
division of cell
what occurs in the division of nucleus stage
mitosis
what occurs in the division of cell stage
cytokinesis
where are chromosomes found?
in the nuclei of the cells
what are chromosomes made of
DNA and protein
what does DNA stand for?
deoxyribonucleic acid
in a cell that is not dividing the chromosomes are in what form?
in the form of chromatin
what does chromatin look like
long, thin threads
what happens to chromatin during cell division
it condenses to chromosomes
what do chromosomes look like in comparison to chromatin?
shorter, thicker and clearly visible
every organism has a distinct
number of chromosomes
most human cells have how many chromosomes
46
each chromosome contains what along its length
each chromosome contains many genes across its length
what is a gene?
a section of DNA that codes for a particular protein
how many genes on human chromosomes
over 30,000
2 things that genes control in humans
eye colour, blood groups etc
3 things that genes control in plants
height
flower colour
seed shape
Human genome project
the sequence of genes on human chromosomes has been mapped, this is the human genome project
how long has the human genome project taken?
10 years to complete it
genome
all the genes present in an organism
in most organisms chromosomes appear in
in pairs
how many pairs of chromosomes in humans
23
how many chromosomes in humans
46
diploid number of chromosomes represented as
2n
in humans, 2n =
46
diploid number
how many pairs of chromosomes an organism has
these pairs of chromosomes are called
homologous chromosomes
diploid cell
2 sets of chromosomes
haploid cells
cells that only have one set of chromosomes
2 cells in humans that are haploid cells
sperm cell
egg cell
haploid cells represented by the symbol
n
in humans n=
23
2 types of cell division
mitosis
meiosis
mitosis
when cells divide, one parent cell gives rise to 2 identical daughter cell
parent cell 2n=
4
daughter cells 2n =
4
body cells, every cell but reproductive cells
somatic cells
when does mitosis occur
in the growth and replacement of cells
somatic cells divide by
mitosis
2 examples of somatic cells
skin cells
liver cells
in plants mitosis occurs in?
meristematic cells
where are meristematic cells found?
in the root tip and shoot tip
meristem
a zone of active cell division
reproduction by mitosis
some simple organisms reproduce asexually by mitosis
2 examples of organisms that can reproduce by mitosis
yeast and amoeba
preparation for mitosis down as
interphase
interphase
the phase between cell divisions during which the cell prepares for the next division
what happens during interphase
DNA replicates
during interphase each chromosome consists of
2 identical strands joined together at a point
2 identical strands joined together at a point
chromatids
centromere
where the 2 chromatids are joined together
what happens when DNA replicates itself
makes an exact copy of itself
why is the replication of DNA very important?
it allows genetic information to be passed fro one generation to the next
what also replicates
cell organelles e.g. mitochondria
why do cell organelles replicate?
to build up the cells energy store
what occurs when cell organelles replicate
protein synthesis occurs
4 stages of mitosis
prophase
metaphase
anaphase
telophase
length of prophase
usually the longest phase
what happens to chromatin during prophase
shortens to form chromosomes
when does DNA replicate
prior to prophase
what happens to the nuclear membrane during prophase
it disappears
what starts to form in prophase
spindle fibres start to form
what forms the spindle fibres
centrioles
what structure do the spindle fibres form
the spindle
what happens to the nucleolus during prophase?
it disappears
what is the function of the nucleolus
makes ribosomes
2 events of metaphase
- the pairs of chromatids become attached to the spindle fibres at their centromeres
- the pairs of chromatids line up across the middle of the spindle
other name for middle of the spindle
equator of the spindle
length of anaphase
this is a rapid phase
events of anaphase
the centromeres split into 2 and the spindle fibres contract and pull the chromatids to opposite ends of the cell. they are now chromosomes
what happens to chromosomes in telophase
when they reach the poles (ends) of the cell the chromosomes uncoil and become chromatin threads
what forms arounds the chromatin in telophase
new nuclear membranes
what happens to the nuclei in telophase
they reappear
cytokinesis
the division of the cell immediately after mitosis
what happens in animal cells during cytokinesis
a cleavage furrow appears which becomes deeper until it eventually divides the cytoplasm in 2
what happens in plant cells during cytokinesis
a cell plate is formed between the two new nuclei
cell wall formation during cytokinesis
a new cell wall forms on either side of the cell plate
what happens to the cell plate then during cytokinesis
becomes the middle lamella
function of middle lamella
cements the cells together
chromosomes in daughter cells
identical to each other and parent cells
cell resulting from mitosis have
identical genes
cells resulting from mitosis are called
clones
cancer
the uncontrolled division of cells (mitosis), producing abnormalities that are passed on to daughter cells
deaths in ireland from cancer
1 in 4 deaths
uncontrolled cell division produces
a mass of cells called a tumour
benign tumours
not life threatening
do not invade other tissues
example of a benign tumour
warts
malignant tumours
invade other tissues and may be life threatening
what causes cancer
when normal genes are changed into cancer causing genes called oncogenes
cancer causing agents
carcinogens
what are responsible for bringing about changes to genes to become oncogenes
carcinogens
3 examples of carcinogens
UV radiation, cigarette smoke, some viruses
what do carcinogens do
they cause changes in the DNA (mutations) which can cause cancer
can cancers be cured
most cancers can be cured if they are caught and treated early
3 treatments for cancer
surgery to remove tumour
radiation to burn out the tumour
chemotherapy to slow down mitosis
4 ways to reduce the risk of cancer
do not smoke
eat a healthy diet
avoid sunburn
self examination for lumps on breasts/testes
meiosis
a form of cell division involving a reduction from the diploid number of chromosomes to the haploid number
meiosis is often called
a reduction division
why is meiosis often called a reduction division
because the number of chromosomes is halved
in meiosis parent cell
2n=4
in meiosis 4 daughter cells
n=2 and non identical
how does meiosis occur in animals
in the formation of gametes
gamete
a haploid sex cell capable of fusion with another sex cell
2 gametes
sperm cell
egg cell
gametes formed by
meiosis
gametes formed by meiosis and are therefore
haploid
when is the diploid number of chromosomes restored in gametes
when fusion of gametes occurs during fertilisation
meiosis leads to
genetic variation in daughter cells
how many new cells (nuclei) formed in mitosis
2
how many new cells (nuclei) formed in meiosis
4
chromosome number in mitosis
stays the same
chromosome number in meiosis
is halved
daughter cells in mitosis
genetically identical to each other and to parent cell
daughter cells in meiosis
genetically different to each other and to parent cell
mitosis occurs in
haploid and diploid cels
meiosis occurs in
diploid cells only
