Cell division, cell diversity and cell differentiation Flashcards
what does the cell cycle consist of
- interphase and mitosis followed by cytokinesis
- IPMATC
why is mitosis essential
- growth
- tissue repair
- asexual reproduction
what are the stages in interphase
G1 (G0), S, G2, M
what occurs in G1
- cell grows
- organelle duplicates
- biosynthesis
what occurs in G0
- rest
- apoptosis or differentiation
- not in all cells
what occurs in S
- DNA replication
what occurs in G2
- cell growth
- proteins made for division
where are the checkpoints during cell cycle
- Metaphase checkpoint
- G1 checkpoint
- G2 checkpoint
role of metaphase checkpoint
- ensures sister chromatids are attached to spindle fibres by their centromeres
role of G1 checkpoint
- cell checks that the chemicals needed for replication are present
- cell checked for any damage to DNA before S phase
role of G2 checkpoint
- cell checks whether all the DNA has been replicated without any damage
describe activities of cells during interphase
- cell continues carrying out normal function but prepared to divide
- DNA is unravelled and replicated
- organelles replicated
- ATP content increased (needed for division)
product of mitosis
2 genetically identical diploid cells
what happens in prophase
- chromosomes condense
- nucleolus and nuclear membrane breaks down
- centrioles move to opposite end of the cell
- spindle fibres form between centrioles
what happens in metaphase
- chromosomes (each with two chromatids) line up at the equator of the cell
- chromosomes become attached to the spindle fibres by their centromeres
what happens in anaphase
- centromeres divide, separating each pair of sister chromatids
- spindle fibres contract, pulling chromatids to the poles
chromosome vs chromatid vs chromatin
- A chromosome consists of a single, double-stranded DNA molecule. ( single ‘unit’ before replication but doubles before cell division, so X is now called chromosome)
- chromatids are two molecules of double-stranded DNA joined together in the centre by a centromere
- chromatin is the complex of DNA and histone protein
what happens in telophase
- chromatids reach the opposite poles on the spindle
- they uncoil becoming long and thin again (they’re now called chromosomes again)
- nuclear envelope forms around each group of chromosomes so there are now two nuclei
what happens in cytokinesis (separate process to mitosis)
- cytoplasm divides
- in animal cells, a cleavage furrow forms to divide the cell membrane
- cytokinesis usually begins in anaphase and ends in telophase
meiosis is reduction division. What does this mean
it halves the chromosome number
mitosis is nuclear division. What does this mean
It is a process where a single cell divides into two identical copies
product of meiosis
- 4 genetically different haploid daughter cells
what are homologous chromosomes
one of a pair of chromosomes with the same gene sequence, loci, chromosomal length, and centromere location
similarities between meiosis 1 and 2
- prophase involves chromatin condensing, nuclear membranes breaking down, and spindle formation
- in metaphase, chromatids line along the equator attached to spindle fibres
- in anaphase, motor proteins draw genetic material to the poles of the cell
- telophase involves the nuclear envelopes reforming
differences between meiosis 1 and mitosis 2
- only prophase 1 involves crossing over
- only metaphase 1 has independent assortment?
- in anaphase 1, chromosomes are pulled apart, but in 2, chromatids are
- telophase 1 is followed by a short interphase.
- Telophase 2 forms 4 haploid cells
what is independent assortment
When the pair of chromosomes splits up (in anaphase), each daughter cell will receive one chromosome. The allocation of this is completely random
outline crossing over
- chromatids twist around one another at chiasmata
- tension is placed on each chromatid, breaking a part off
- broken sections re-join with the other homologous partner
Each homologous chromosome will go to the two daughter cells. the total number of combinations is…….(equation)
- 2^n
- n= number of chromosomes in haploid cell
what are stem cells
unspecialised cell able to express all of its genes and divide by mitosis
how do cells differentiate
- genes switch off, forming specialised cells and tissues
what things can be altered by differentiation in cells
- shape
- size
- contents and organelle proportions
define differentiation
the process by which all cells become specialised into different cell types
what are stem cells used for in adults
- replace damaged cells
what can plant stem cells differentiate into
- xylem and phloem
what do stem cells in bone marrow differentiate into
blood cells to replace those lost or produce neutrophils to help fight infections
where are stem cells in plants
- meristematic tissue in meristems (found in shoot tips, roots and cambium of vascular bundles)
vascular cambium vs meristem
The vascular cambium is a layer of meristematic cells
application of stem cells
- researching developmental biology
- replaced damaged cells in disorders like Alzheimer’s and Parkinson’s
how can stem cells be used to treat in Alzheimer’s
- nerve cells in brain die in increasing numbers resulting in memory loss
- researchers are hoping to regrow healthy nerve cells
how can stem cells be used to treat in Parkinson’s
- patients suffer from tremors that they can’t control
- This disease causes the loss of a particular type of nerve cell found in the brain that release dopamine
- Transplanted stem cells may help to regenerate the dopamine-producing cells
how can stem cells be used in developmental biology
- research into how organisms grow and develop
- help understand disorders and cancer
sources of stem cells
- embryos
- umbilical-cord blood
- bone marrow
- induced pluripotent stem cells, iPS ( genes in cells switched on in lab to make them undifferentiated)
define pluripotent
capable differentiating into several different cell types
examples how can stem cells be used to repair damaged tissue
- treat mice with type 1 diabetes by programming iPS cells to become B cells
- bone-marrow stem cells made to develop into hepatocytes to treat liver disease
- used in regenerative medicine to grow organs for transplanting, if patients’ cells obtained turned into iPS then there’s no need for immunosuppressant drugs
- may eventually be used to treat burns and vision loss
why do multicellular organisms need specialised cells and tissues to survive
small SA:V
define tissue
a group of similar cells working together to perform the same specific function
define organ
a group of similar tissues working together to perform the same specific function
define organ system
a group of organs working together to perform the same specific function
difference between the functions of erythrocytes and neutrophils
- erythrocytes carry oxygen from the lungs to respiring cells
- neutrophils ingest invading pathogens
how are erythrocytes specialised
- very small so large SA:V (easy diffusion of O2 into cell)
- flexible due to well developed cytoskeleton so can twist and turn as it travels through narrow capillaries
- most organelles lost at differentiation which provides more space for Hb in them
how are neutrophils specialised
- twice the size of erythrocytes with multilobed nucleus
- attracted to sites of infection by chemotaxis
- function is to ingest bac and fungi by phagocytosis
how are sperm cells specialised
- many mitochondria for ATP for energy which allows tail to move and propel cell towards the ovum
- small, long and thin so they can move easily
- head has acrosomes that digest outer layer of ovum so sperm cell can enter
- head contains haploid male gamete nucleus and very little cytoplasm
how are epithelial cells specialised
- lining tissue
- squamous epithelial cells are flattened in shape
- many have cilia
how are palisade cells specialised
- long and cylindrical so can pack together closely but little space between cells so CO2 in these air spaces diffuse into cells
- large vacuole so chloroplasts near periphery of cell so short diffusion diffusion distance for CO2
- many chloroplasts
- cytoskeleton and motor proteins move chlorophyll nearer to upper surface when light intensity is low but further down when its high
how are guard cells specialised
- in lower epidermis so don’t photosynthesise
- light energy used to produce ATP
- ATP used to for active transport of K+ into cell to lower water pot so water moves into cell by osmosis
- guard cell swells but as tips of cell wall are more flexible and more rigid at the thicker middle part, stomata enlarges
- open stomata allow gas exchange and as CO2 is used for photosynthesis, conc gradient is maintained
- transpiration is an inevitable consequence when stomata are open
how are root hair cells specialised
- hair-like projections increases SA for absorption of water
- mineral ions actively transported into cell by special carrier proteins
- ATP produced for the process
features of epithelial tissue: ciliated and squamous
- lines organs, airways and tubes
- has a role in absorption, secretion and protection
- cells attach in sheets and receive nutrients via diffusion from tissue fluid in connective tissue ( as epithelial tissue has no blood vessels)
- cell have short cell cycles as it replaces cells regularly
features of connective tissue
- consists of cells and non-living matrix
- Cartilage is a type of connective tissue that adds structural strength and cushions joints
features of muscle tissue
- contracts using long protein filaments which contain actin and myosin proteins, these myofilaments allow contraction
- well vascularised
- 3 types:
- smooth lining tubes and propels substances along them
- skeletal for movement
- cardiac in heart which allows heart to beat and pump blood
features of epidermal tissue
- flattened sheets of cells forming a protective covering for the leaf
- some cell walls impregnated with waxy substance to reduce water loss
what’s the vascular bundle in plants composed of
- xylem vessels which carry water and minerals from roots to all parts of the plant
- phloem sieve tubes which transfer sucrose in solution from leaves to all parts of the plant that don’t photosynthesise (roots, flowers)
features of plant stem cells
- thin walls with very little cellulose
- no chloroplasts
- don’t have a large vacuole
- divide by mitosis and differentiate into other cell types
how do cambium cells differentiate into xylem vessels
- lignin deposited in cell walls to reinforce and waterproof cells but this kills them
- ends of cells break down forming continuous columns with wide lumens to carry water and minerals
how do cambium cells differentiate into phloem sieve plates
- most organelles lost, sieve plates develop between cells
- companion cells retain organelles and continue metabolic functions for active loading of sugars into sieve tubes
