M2, C6 Cell Divisions Flashcards
what happens during interphase
- DNA is replicated and checked for errors in the nucleus
- protein synthesis occurs in the cytoplasm
- mitochondria grow and divide, increasing in number
- in plant cells chloroplasts grow and divide
- normal metabolic process occur like respiration
what are the three stages of interphase
G1 - protein synthesis, organelles replicate, cell increases in size
S - synthesis phase: DNA is replicated in the nucleus
G2 - cell continues to increase in size, energy stores increase and duplicated DNA is checked for errors
what stages does the mitotic phase include
mitosis - nucleus divides
cytokinesis - cytoplasm divides and two cells are produced
why would a cell enter G0 phase
- for a cell that becomes specialised and no longer is able to divide
- the DNA could be damaged so is no longer viable
what does it mean if a cell is senescent
it can no longer divide
you get more of these cells as you age which leads to the risk of disease
why are their checkpoints in the cell cycle
ensure the cell only divides when it has grown to the right size, there are no errors and the chromosomes are in the correct positions
what does the G1 checkpoint check for
cell size
nutrients
growth factors
DNA damage
if these are there then the cell enters S phase
if not it enters G0
what does the G2 checkpoint check for
cell size
DNA replication
DNA damage
if satisfactory then the cell enters the mitotic phase
if not then it enters resting state
what does the spindle assembly checkpoint check for
chromosome attachment to spindle
mitosis doesn’t proceed unless this checkpoint is passed
define mitosis
a type of cell division that resuslts in 2 daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth
why is mitosis important
growth
repair tissues
asexual reproduction
what is the centromere
the region of a chromosome to which the microtubules of the spindle attach during cell division.
what are chromatids
each of the two thread-like strands into which a chromosome divides longitudinally during cell division. Each contains a double helix of DNA.
what are the phases of mitosis
prophase metaphase anaphase telophase cytokinesis
what happens in prophase in mitosis
mitosis begins
chromatin condenses and becomes inactive
centrioles migrate in pairs to opposite poles and the nuclear evelope and nucleolus break up
the chromosomes are now tightly coiled and visible as separate bodies under the microscope
the mitotic spindle begins to form at the centrioles
what is chromatin
Uncondensed DNA in a complex with histones
what happens during the metaphase in mitosis
the mitotic spindle grows further and attaches to the centromere of each chromosome
the fibres then arrange the chromosomes to line up along the cell equator
what happens during anaphase in mitosis
- the centromere of each chromosome breaks
- sister chromatids (identical chromosomes held by the centromere) separate into daughter chromosomes
- chromatids pulled to opposite poles by shortening of spindle microtubules
what happens during telophase in mitosis
- Each sister chromatid now at each pole
- new nuclear membranes forms around new sets of chromosomes at each pole
- the chromosomes start to uncoil back into chromatin and are no longer visible under the microscope
what happens during cytokinesis in animal cells
the cytoplasm is divided between the 2 daughter cells to finish the cycle
each new cell enters interphase and resumes its normal functions
Cleavage furrow formed in the middle of the cell. cell-surface membrane pulled inwards by cytoskeleton and fuse forming two cells.
what happens during cytokinesis in plant cells
vesicles from the Golgi apparatus begin to assemble between the two nuclear envelopes
the vesicles fuse with each other and the cell surface membrane divides the cell into 2
new sections of the cell wall then form along the new membrane which splits the cell
how are gametes formed
meiosis
why is a gamete said to be haploid
contains half the chromosome number of the parent cell
what are homologous chromosomes
a pair of same chromosomes, one from each parent
have the same genes but can different alleles of each gene
what are alleles
different versions of the same gene
the genes have the same locus and the centromeres will be in the same position
in meiosis 1 what happens during prophase
- chromosomes condense
- nuclear envelope disintegrates
- spindle formation begins
- homologous chromosomes pair up, forming bivalents
- chromatids entangle and alleles are exchanged between homologous chromosomes = crossing over (genetic variation) still same genes just different alleles (expression of genes)
in meiosis 1, what happens during metaphase
- spindle fibres attach to centromere
- homologous pairs of chromosomes assemble along the metaphase plate
- the orientation of the pair is random = the maternal or paternal chromosomes can end up facing either pole = independent assortment (genetic variation)
in meiosis 1, what happens during anaphase
- each chromosome from the homologous pair are pulled to opposite poles and chromatids stay joined together
- the entangled chromatids break off and rejoin (at the chiasmata) (NOT CROSSING OVER THO)
in meiosis 1, what happens during telophase
- chromosome assemble at each pole
- nuclear membrane reforms
- chromosomes uncoil
- cell undergoes cytokinesis and divides into 2 cells
-the reduction of chromosome number from diploid to haploid is complete
in meiosis 2, what happens during prophase 2
- DNA condense and become visible again
- nuclear envelope breaks down
- spindle formation begins
Same as mitosis except that chromatids no longer identical due to crossing over
in meiosis 2, what happens during metaphase 2
- the individual chromosome assemble on the metaphase plate through attachment to spindle fibres to their centromeres.
- chromatids randomly assorted at either side of the equator (genetic variation)
in meiosis 2, what happens during anaphase
chromatids of the genetically different chromatids are pulled to opposite poles after division of the centromeres
in meiosis 2, what happens during telophase
-chromatids assemble at the poles
-chromosomes uncoil and form chromatin again
-nuclear envelope reforms
-cytokinesis results in division of the cells forming 4 daughter cells
the cells will be haploid due to the reduction division
they are all genetically different from each other and the parent cell
what does a differentiated cell mean
they are specialised to carry out very specific functions
how are erythrocytes specialised
have a flattened biconcave shape
increases surface area : volume
essential for transporting oxygen
no nucleus or organelles to maximise space for haemoglobin
flexible to squeeze through narrow capillaries
how are neutrophils (type of white blood cell) specialised
have a multi-lobed nucleus so they can squeeze through small gaps to get to the site of infection
contain many lysosomes to attack pathogens
how are sperm cells specialised
tail or flagellum for movement
lots of mitochondria to supply energy
acrosome on the head contains digestive enzymes to break through the egg
how are palisade cells specialised
contain lots of chloroplasts which can move in the cytoplasm to absorb large amounts of light for photosynthesis
rectangular box shape to tightly pack in a continuous layer
thin cell walls for increased diffusion of co2
large vacuole to maintain turgor pressure
how are root hair cells specialised
long extensions called root hairs to increase surface area
maximises uptake of water and minerals from the soil
how are guard cells specialised
when guard cells lose water and become less swollen as a result of osmotic forces - they change shape and the stoma closes to prevent further water loss
cell wall is thicker on one side so cell doesn’t change shape symmetrically as its volume changes
what are the 4 main categories of animal tissues
nervous tissue
epithelial tissue
muscle tissue
connective tissue
how is squamous epithelium tissue specialised
very thin - one cell thick
for rapid diffusion
forms the lining of the lungs for diffusion of oxygen into the blood
how is ciliated epithelium tissue specialised
cilia that move in a rhythmic manner to move mucus along
goblet cells are also present to release mucus to trap pathogens
how is cartilage tissue specialised
connective tissue
contains elastin and collagen
firm and flexible
prevents ends of bones rubbing together
how is muscle tissue specialised
able to shorten in length in order to move bones
contains contractile proteins and myofibrils
how is epidermis tissue specialised
covered by a waxy, waterproof cuticle to reduce loss of water
closely packed cells
contains stomata which can open and close due to the guard cells
allows water, oxygen and carbon dioxide in and out
how is xylem tissue specialised
composed of dead cells
walls are strengthened by lignin which is waterproof
structural support for plants
how is phloem tissue specialised
composed of columns of sieve tube cells separated by perforated walls called sieve plates
transported organic nutrients from leaves and stems to parts of the plant where it’s needed
define an organ
collection of tissues that are adapted to perform a particular function in an organism
give examples of animal organ systems
digestive system cardiovascular system (movement of blood) gaseous exchange system
what organs are involved in the digestive system
oesophagus rectum stomach large intestine small intestine liver mouth anus
what organs are involved in the nervous system
nerves
brain
what organs are involved in the urinary system
bladder
ureter
kidneys
urethra
what organs are involved in the circulatory system
veins
arteries
heart
capillaries
what organs are involved in the respiratory system
trachea
bronchi
bronchioles
lungs
what organs are involved in the musculoskeletal system
muscles
bones
what are stem cells
undifferentiated cells so they don’t have a specific function
they have the potential to differentiate into a specialised cell
what is the term for a stem cells ability to differentiate
potency
define totipotent
these stem cells can differentiate into any type of cell, forming a whole organism
eg. a fertilised egg
define pluripotent
these stem cells can form all tissue types but not whole organism
define multipotent
these stem cells can only form a range of cells within a certain type of tissue
what stem cells have blood cells derived from
stem cells in the bone marrow
what are the sources of animal stem cells
embyros - these are totipotent
tissues like bone marrow - these are multipotent
umbilical cords - multipotent
what are the sources of plant stem cells
meristematic tissue (meristems) - found wherever growth is occurring in plants or between xylem and phloem - it is pluripotent
what are the potential uses of stem cells
heart disease - repair muscle tissue in the heart
type 1 diabetes - for insulin-producing cells
Parkinson’s disease - for dopamine-producing cells in the brain
Alzeihmer’s disease - brain cells
macular degeneration - treat blindness
birth defects
spinal injuries
what are stem cells currently being used for
treatment of burns - new skin
drug trials - can be tested on stem cells before animals
developmental biology
what are the reasons for using stem cells
- saves lives
- improves peoples lives
- embryos have been donated, were going to be discarded of anyway
- could save NHS lots of money as people wouldn’t need medicine or operations
what are the reasons against using stem cells
- embryos are destroyed
- religious objections - belief life begins at conception so destroying embryos is murder
- costs a lot of money - too much of a risk
