chapter 6- cell division Flashcards
how much of a cell life does it spend in interphase
90-95%
how many divisions take place in mitosis
1 nuclear
1 cytoplasmic
daughter cells are what to the parent cell
genetically identical to the parent cell
in eukaryotes the cell cycle is divided into 2 major phases
interphase and the mitotic phase
is interphase an active or passive phase and what does that mean
active as respiration occurs
what are the 3 phases in interphase
gap/growth stage (G1)
synthesis (S)
gap/growth stage (G2)
what happens in G1
getting dna ready to replicate
cytoplasm increases in volume as it will need to be shared (so growth in cell size)
production of proteins for organelles to be replicated
types of rna (biochemicals) made ready for s phase
organelles synthesised
what happens in the S phase
dna replication so that its ready for mitosis
what happens in the G2 phase
ATP levels increased ready for mitosis
increases in cell size due to increase in cytoplasm volume.
error checking of dna
where is the centromere located
in the centre of a chromosome
in a relicated chromosome (x) what are the 2 branches called
sister chromatids
what is a pair of homologous chromosomes
The two chromosomes in a homologous pair are very similar to one another and have the same size and shape. Most importantly, they carry the same type of genetic information: that is, they have the same genes in the same locations. However, they don’t necessarily have the same versions of genes.
what is never visible in interphase
chromosomes
how long does the cell cycle take for a human cell
24hrs ish
what are the 3 stages of the cell cycle and put them in order of size
interphase
mitosis
cytokinesis
the cell cycle in not a life cycle as it happens
repeatedly
chromatin is wrapped around
histone proteins
what is not visible in interphase
chromosomes, so dna is visible as chromatin
an x looking chromosome means that
the chromosomes have been replicated
what happens at the G1 (end) checkpoint
check for:
nutrients (energy)
growth factors
dna damage
if the G1 checkpoint fails then what will happens
it will enter G0
how can cancer cells replicate freely
they reproduce quickly and over produce growth factors and so can slip through the checkpoints
what happens at g2 checkpoint
check for:
cell size
dna replication (faults)
if there is a fault then the process pauses and it will be repaired, otherwise faulty dna will be passed on daughter cells
which stage of mitosis has a checkpoint
metaphase
what happens at the metaphase checkpoint
checks that all the chromosomes are attached to spindle fibres and that they are aligned
chromosome/dna activity in interphase
dna replicates but is visible as chromatin not chromosomes
status of the nuclear envelope in interphase
present and intact, complete
what else happens in interphase but only in animal cells
centrioles replicate
Animal cells contain an organelle called the ……… which is made up of two structures called ……..
This is where ………. form during metaphase.
centrosome
centrioles
spindle fibres
what is the chromosome activity in prophase
early: chromatin condenses and coils to form chromosomes (into pairs of sister chromatids this will appear darker as it will take up more stain
status of the nuclear envelope in prophase
it breaks down but only later on
what happens to the sf in prophase
they form from the centrioles and migrate to the poles
chromosome activity in metaphase
align at the equator on the metaphase plate which is held in place
status of the nuclear envelope in metaphase
not present
sf activity in metaphase
they attach to the centromeres of the chromosomes
which phase of mitosis is the longest and why
metaphase because it has a checkpoint
chromosome activity in anaphase
sister chromatids separate
is there a nuclear envelope in anaphase
no
sf activity in anaphase
sf contract (shorten) pulling the sister chromatids apart and towards the poles
what shape does the sister chromatid make when it is pulled by a sf
a v shape
chromosome activity in telophase
chromatids assemble at opposite poles
chromatids condense back into chromatin
status of nuclear envelope at telophase
reforms around each set of chromosomes at each pole
what else happens in prophase
the nucleolus breaks down
what else happens in telophase
the nucleuolus reforms
sf activity in telophase
they breakdown and detatch from sister chromatids
why is mitosis important
tissue repair and replacement of damaged cells
organism growth: derive new cells via mitosis
asexual reproduction
development of embryos: zygotes undergo mitosis and differentiate to become embryos > multicellular organisms
what does the centromere do
keeps the 2 sister chromatids together
sf attach to the kineticore
what is used for looking for faults in dna
carrier type
do prokaryotes carry out mitosis
no
how long do rbcs live for
120 days
how many divisions does meiosis
2 nuclear
2 cytoplasmic
what type of cells does mitosis make
somatic
what type of cells does meiosis make
gametes
does crossing over occur in mitosis or meiosis
meiosis
reason for meiosis
to make gametes for sexual reproduction, without haploid gametes a diploid zygote would not be possible
in asexual reproduction there is no ……. as the offspring are…….. of the parent. this is because they inherit the same …… as the parents.
variation
clones
genes
in sexual reproduction each …… is different. therefore when…… occurs chromosomes from the father mixed with chromosomes from the mother so the offspring have a combination of ….. giving rise to variation
gamete
fertilisation
alleles
gametocytes (germline cells) are what
eukaryotic germ cells that divide by meiosis into gametids during gametogenisis
male gametocytes are called
spermatocytes
female gametocytes are called
oocytes
what happens in prophase I in meiosis
dna condenses and chromosomes become visible
homologous chromosomes undergo synapsis whereby they pair up to form a bivalent,
are held together at points called chiasmata.(where the crossing over occurs)
centrioles migrate to the opposite poles and the spindle is formed
the nuclear envelope breaks down and the nucleolus disintegrates
which stage does crossing over occur in meiosis
prophase 1 ONLY
how many bivalents in a human cell
23 (a pair of chromsomes=1)
result of prophase 1
physical change of genetic material and all 4 haploid daughter cells will be genetically distinct as the sister chromatids will no longer be identical
once the chiasmata are formed the homologous chromosomes fully condense as bivalents and then are separated (later)
what happens in metaphase 1
the bivalents line up along the equator (mp) of the spindle (RANDOMLY) with the sf attached to the centromeres. independent assortment occurs. nuclear membrane fully breaks down
what is independent assortment
occurs during metaphase 1. the maternal and paternal pairs of chromsomes position themselves separate from the others and can end up facing either pole (orientation) so can result in many different combinations of alleles facing the poles, IA results in genetic variation
what happens in anaphase 1
the homologous pairs are pulled by sf to the opposite ends of the spindle (whole chromosomes), the centromeres do not divide
v shape created
what happens in telophase 1
sf start to break down
nuclear envelopes start to form around the 2 groups of chromosomes and nucleoli reform.
what can be different about plant cells in meiosis
some go straight to meiosis 2 without the reformation of the nucleus in telophase 1
process of cytokinesis in animals 3/4
cell surface membrane pinches inwards, by the cytoskeleton, creating a cleavage furrow in the middle of the cell which contracts dividing the cytoplasm in half
cleavage furrow forms around the middle of the cell and the cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle forming two cells
cytokinesis in plants
plant cells have cell walls so a cleavage furrow cannot form.
vesicles from the golgi begin to assmble in the same place the metaplate was formed.
what else generally happens in cytokinesis
the cell organelles also get distributed between the 2 developing cells
there is no ……… between meiosis 1 and meiosis 2 so the dna is … ……..
interphase
not
replicated
what happens in prophase 2
the nuclear envelope breaks down and chromosomes condense
a spindle forms at a right angle to the old one
there is no pair of chromosomes so crossing over cannot occur
what happens in metaphase 2
chromosomes line up in a single file along the equator of the spindle, IA can occur
define stem cell
a cell that is unspecialised and undifferentiated
which is true about stem cells
a) stem cells naturally divide to produce a new organism
b) stem cells in adult humans can divide into a limited range of cell types
b
what 2 qualities of stem cells
self renewal and potency
what is self renewal
they can continuously divide and replicate
what is potency
they have the capacity to differentiate into specialised cell types
what is the potency and source of totipotent stem cells
p: can form any cell type including extra embryonic tissue (total potential), can differentiate into any cell and are capable of forming whole organisms
s: zygote during the first mitotic divisions (first 1-4 days)
potency and source of pluripotent (embryonic) stem cells
p: can form any cell type but cannot form whole organisms, can differentiate into most cells
s: early embryos/blastocysts
potency and source of multipotent (adult) stem cells
p: can differentiate into a number of closely related cell types within a tissue
s, can differentiate into a limited number of cells
s: bone marrow
Multipotent stem cells are found in the bone marrow. What two cell types can they differentiate into?
erythrocytes and neutrophils.
what are haemopoietic stem cells
multipotent, found in bone marrrow and long bones not brain or muscle
unipotent stem cells
cannot differentiate but can self renew eg muscle stem cells
Which of the following are issues with using stem cells in scientific study?
the collection of stem cells from embryos destroys the embryo.
Some people have moral objections to this because they argue that embryos are living beings.
Additionally, harvesting stem cells from bone marrow is painful for the donor and there is a risk that the patient’s immune system will reject the donated cells.
red blood cells are also known as `
erythrocytes
what is the shape of an rbc and why is it beneficial
flattened biconcave shape which increases sa to v ratio so they can carry more o2
in mammals what do rbcs not have
nuclei or many other organelles which increases space for haemoglobin which carried o2
rbcs are also flexible so….
they can squeeze through narrow capillaries
chloroplasts in palisade cells can
absorb large amounts of light for photosynthesis and can move within cytoplasm in order to absorb more light
palisade cells are present in the
mesophyll
the vacuole in palisade cells..
is large to maintain turgor pressure and is rectangular so that things can be tightly packed around it to form a continuous layer
the cell wall in palisade cells is thick/thin…..and why
thin to increase ror
root hair cells have many
mitochondria to provide atp for active transport of minerals into the cell
where are rhc present
at the surface of roots near the growing tips, long extensions called root hairs which increases the sa of the cell to maximises uptake of water and minerals from the soil.
rhc have a large vacuole…
containing cell sap- solutions of ions and sugars which lowers water potential
How is eukaryotic DNA similar to prokaryotic DNA?
Their nucleotide structure is identical
Their nucleotides are joined by phosphodiester bonds
which has extrons and introns for pro and eu
eu dna has both
pro dna only has exons
Describe how chromosomes are formed.
First, DNA condenses into chromatin by wrapping tightly around histones. Then, this structure folds together to form a chromatid (one arm of a chromosome).
what is a telomere
One place DNA is found in eukaryotic cells is the nucleus.
Name two other organelles that contain DNA.
mitochondria and chloroplasts.
Some prokaryotes contain small, circular molecules of DNA called…
plasmids
compare the number of cell division and daughter cells from mitosis and meiosis
mitosis: 1 cell division and results in 2 daughter cells.
meiosis is 2 and 4
During meiosis I, chromosomes that carry the same genes pair up.
these pairs are called
homologous chromosomes
What happens during meiosis II? the sister …
The sister chromatids move apart from each other to form two pairs of daughter cells.
During meiosis, sister chromatids are pulled to opposite poles of the cell.
anaphase 2
Pairs of homologous chromosomes line up along the equator of the cell.
Which stage of meiosis is this describing?
metaphase 1
Four nuclear envelopes form.
Which stage of meiosis is this describing?
telophase 2
explain how independent assortment gives rise to genetically varied gametes (2)
random arrangement of chromosomes
maternal and paternal chromosomes/chromosomes from homologous pairs
describe how crossing over gives rise to different combinations of alleles in gametes (2)
exchange of alleles
between non sister chromatids
Describe how crossing over in meiosis leads to genetic variation (3 things)
During meiosis 1, homologous chromosomes twist around each other. Then, portions of alleles are exchanged and this produces a new combination of alleles in each chromosome. `
Describe how independent assortment in meiosis leads to genetic variation (2 things)
During meiosis 1, the homologous chromosomes line up at random. This creates different combinations of chromosomes
