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
define zygote?
the cell formed in sexual reproduction from the fusing of an egg and a
sperm
define maternal chromosomes?
set of chromosomes in an individual’s cells that were contributed by the egg
define paternal chromosomes?
set of chromosomes in an individual’s cells that were contributed by the sperm
define homologous pairs?
chromosome pairs of approximately the same length, centromere position, and staining pattern, with genes for the same
characteristics at corresponding loci. One homologous chromosome is inherited
from the organism’s mother; the other from the organism’s father
define chromatid?
either of the two daughter strands of a replicated chromosome that are joined by a single centromere and separate during cell division to become individual chromosomes
define chiasmata?
the point where non-sister chromatids join and cross over (single = chiasma)
define crossing over?
where lengths of DNA are swapped from one chromatid to another
define bivalent?
a pair of joined (synapsed) homologous chromosomes during prophase and metaphase of meiosis I
define allele?
a version of a gene that is expressed as a slightly different polypeptide
define locus?
the position of a gene on a chromosome
what is prophase I?
chromatin condenses and supercoils
chromosomes come together in homologous pairs to
form a bivalent (one maternal and one paternal)
non-sister chromatids wrap around each other and attach at chiasmata
sections of chromatids are swapped – crossing over nucleolus disappears and nuclear envelope
disintegrates
spindle forms
define metaphase I?
bivalents line up at the cell’s equator
spindle fibres attach to centromeres
bivalents are arranged randomly (independent assortment), with
each member of a homologous
pair facing opposite poles – this
allows chromosomes to independently segregate when
pulled apart
define anaphase I?
homologous chromosomes in each bivalent are pulled to opposite poles by the spindle fibres
centromeres do not divide
chiasmata separate and lengths of chromatid which have been exchanged in
crossing over remain with their newly attached chromatid
define telophase I in animal cells and plant cells?
animal cells – nuclear envelopes re-form and cell divides by cytokinesis. Brief interphase (but no DNA replication), chromosomes uncoil
plant cells – No telophase I. Cell progresses straight from anaphase I to meiosis II
define prophase II?
if a nuclear envelope has reformed, it breaks down again
the nucleolus disappears, chromatin condenses and spindles form
define metaphase II?
chromosomes line up at the cell’s equator and spindle fibres attach to centromeres
chromatids are arranged randomly (independent assortment)
define telophase II?
nuclear envelope reforms around haploid daughter nuclei
animal cells – two cells divide to give four haploid cells
plant cells – tetrad of four haploid cells is formed
what are the four sources of variation in meiosis?
random mutations can occur during interphase when the DNA replicates
crossing over (prophase 1)
independent assortment of chromosomes
(metaphase 1)
independent assortment of chromatids
(metaphase 2)
what happens in the crossing over stage?
fragments of chromatid may get swapped over and genetic material is exchanged between the chromosomes. This will create variation as the chromatids still contain the same genes but now have a different (new) combination of alleles
what’s independent assortment of chromosomes?
independent assortment means that
the inheritance of one chromosome is
independent of the inheritance of
others
either chromosome from each
homologous pair can pass into the
gamete
this means that each gamete receives
a different combination of maternal
and paternal chromosomes
what can fertilisation lead to?
genetic variation because any one of approximately 300 million sperm, each with its own genetic material, can fertilise the egg
what does fertilisation increase?
genetic variation by randomly combining
two sets of chromosomes, one from each of two genetically unrelated individuals
define stem cells?
stem cells are undifferentiated cells that
are capable of differentiating to form specialised cells with a particular function
name the different ways that cells can differentiate?
cell shape, cellular contents or the abundance of a particular organelle
what are the two types of cells that stem cells come from?
embryonic and adult stem cells
what are embryonic stem cells and what happens when we remove these types of stem cells?
these stem cells come from embryos
that are three to five days old
removing stem cells kills the embryo
stem cells are totipotent or pluripotent what does this mean?
means they can become any type of cell in the body
define totipotent?
stem cells which can form ANY type of cell in the
embryo (220+ types) PLUS cells of the placenta. These are the most versatile
define pluripotet?
stem cells which can form ANY type of cell in the
embryo (but NOT placental cells). These are a little less
versatile than totipotent cells
define multipotent?
adult stem cells which can form a limited number
of cell types; e.g. haemopoietic stem cells in the bone marrow
forming erythrocytes and leucocytes. These are the least
versatile
what is bone marrow used for?
widely-used treatment for leukaemia, sickle-cell anaemia and immune disorders
treatment – the patient’s own bone
marrow cells are removed and frozen, then returned to the body after chemotherapy
what can drugs be tested on (not on animals)? and why?
drugs can be tested on human stem cells grown in a lab rather than on animal tissues – gives a more valid result
as animal cells may not always respond in exactly the same way to a drug as human cells would
why do we study development biology?
help scientists understand how organisms grow, develop and mature
observe how differentiation occurs and see what the consequences
are if there is a developmental issue
what could growing cells/tissues/organ for transplant possibly treat?
could potentially treat type-1 diabetes by making replacement pancreatic cells (tests on mice successful, human research is ongoing)
could potentially grow nerve tissue to treat degenerative conditions like Alzheimer’s (memory loss caused by death of many brain cells) and Parkinson’s (loss of types of brain cell leading to uncontrolled muscle tremors) and to repair spinal cord injuries
leading to paralysis
could potentially grow replacement heart cells to treat patients who have experienced heart disease or a heart attack
state the problems with using stem cells?
scientists don’t yet know how to turn off or on all of the genes found in stem cells. This means that it is very difficult to produce specific types of cells
making useful differentiated cells from stem cells is very expensive, slow and difficult to control. Scientists often
don’t know which specific cell signalling molecules are required to cause stem cells to differentiate into a particular type of specialised cell. Sometimes tumours form
some religious groups feel that as many stem cells are taken from embryos, there is an ethical argument about exploiting one life to benefit another. There are less ethical issues linked to the use of adult stem cells as they are donated with consent and donation causes no lasting harm
what are the two main blood cell types?
neutrophils (white blood cells that
help fight infection)
Red blood cells
(erythrocytes)
what happens to the cells that are destined to become erythrocytes?
lose their nucleus,
mitochondria, Golgi apparatus and RER, and are filled with haemoglobin.
Their shape also changes to a biconcave disc, allowing them to
squeeze through narrow capillaries and providing a larger surface area
for transporting oxygen
what happens to the cells that are destined to become neutrophils?
keep their nucleus and are full of mitochondria. They appear granular
because of the presence of many lysosomes (which contain enzymes to
destroy pathogens)
what are the plants equivalent of a blood vessel and where are they found?
vascular bundles and they are found in plant roots and stems
what are vascular bundles made of?
vascular bundles are made
up of phloem and xylem
tissue, plus cambium
(contains stem cells)
what do cambium cells differentiate to become?
cambium cells differentiate to become new xylem or phloem cells as needed
what is the function of xylem vessels & phloem vessels?
xylem vessels carry water and dissolved mineral ions up the stem
phloem vessels carry sugars made in photosynthesis around the plant
state some specialised cells in animal cells?
sperm cell/egg cell erythrocyte (RBC) neutrophil (WBC) epithelial cell rod cell/cone cell goblet cell fat cell motor/sensory neurone muscle cell
state some specialised cells in plants?
palisade cell root hair cell guard cells xylem cell phloem cell companion cells
define a tissue?
a tissue is a group of similar cells that work together to
perform a specific function
state the four main animal tissues?
connective tissue
epithelial tissue
muscle tissue
nervous tissue
what are the two groups that epithelial tissue splits into?
simple epithelium - one layer thick; lines the respiratory tract, blood vessels, and forms glands in the digestive tract
stratified epithelium - several layers thick; lines the skin, mouth, and anal canal
what do squamous epithelium form?
flattened cells that form a smooth and thin surface suitable for lining
organs and tubes including
blood vessels
form the walls of alveoli – being so thin provides
a very short diffusion
pathway for gases
what do ciliated epithelium form?
long, narrow cells that are often described as “columnar”
where is ciliated epithelium found?
found in the respiratory system (trachea, bronchi and larger bronchioles) and the reproductive system
(fallopian tubes and uterus)
what are the three types of muscles?
involuntary or smooth
muscle – found in the gut,
artery walls, bronchi,
cervix and uterus
voluntary or skeletal
muscle – cause bones to
move
cardiac muscle (walls of the heart)
what is cartilage?
connective tissue found in joints (e.g. the knee) and between vertebrae
also shapes and supports the nose, ears and trachea
where is cartilage found?
formed when cells called chondroblasts secrete an extracellular matrix (jelly-like substance containing protein fibres). This matrix traps the chondroblasts
what is the role of the leaf (organ) and leaf tissues?
is to carry out photosynthesis
each of the leaf tissues has
a particular role to play in
maximising the rate of
photosynthesis
what do epidermal tissues form?
they form a covering over
leaves, stems and roots
what are epidermal cells features?
generally epidermal cells are flattened and lack
chloroplasts (except for guard cells). Some also have a waxy substance embedded in their walls to form a waterproof cuticle to reduce evaporation
