mitosis Flashcards
define mitosis
nuclear division stage in mitotic phase of cell cycle
define chromosome
condensed and coiled DNA in the form of chromatin
define chromatids
one of the two halves of a replicated chromosome
define sister chromatids
identical copies formed by DNA replication of a chromosome with both copies joined together by a common centromere
define centromere
region at which two chromatids are held together
define spindle fibres
structures composed of microtubules that organise chromosomes and pull them apart to opposite poles during mitosis
define homologous pairs
matching pair of chromosomes, one inherited from each parent
describe how DNA is packaged in a chromosome
- DNA is associated with proteins (histones)
- DNA wraps around making it more compact (chromatin)
- interphase: chromatin is decondensed
- mitosis - chromatin is condensed (chromosomes)
list the stages of mitosis in order
- prophase
- metaphase
- anaphase
- telophase
describe what happens during interphase
- chromatin fibers coil & condense = chromosomes (visible if stained)
- nucleolus disappears, nuclear membrane breaks down
- microtubules form spindle fibers
- centrioles migrate to opposite poles of cells
- spindle fibers attach to specific areas on centromeres, start moving chromosomes to center
- nuclear envelope has disappeared by end
describe what happens during metaphase
chromosomes are moved by spindle fibers + line up along the equator of the cell
describe what happens during anaphase
- centromeres holding pairs of chromatids in each chromosome divide
- chromatids pulled to opposite ends by shortening of spindle fibers
describe what happens during telophase
- chromatids have reached the poles as chromosomes
- two new sets of chromosomes assemble at each pole
- nuclear envelope reforms around chromosomes
- chromosomes uncoil, nucleolus is formed
- cytokinesis begins
explain the role of centrioles in mitosis
organise spindle fibres which are attached to them
explain the role of spindle fibres in mitosis
pull chromatids to opposite poles and ensure even chromosome distribution between daughter cells
describe the process of cytokinesis in animal cells
- cleavage furrow forms around middle of the cell
- plasma membrane pulled inwards by cytoskeleton until close enough to fuse
- two cells are formed as a result
describe the process of cytokinesis in plant cells
- vesicles from Golgi assemble on metaphase plate
- vesicles fuse with each other + CSM, dividing cell into two
- new sections of cell wall form along new sections of membrane
what is osmotic lysis
if dividing cell wall forms before daughter cells have separated, surrounding water causes osmotic lysis
why does a cleavage furrow not form in plant cells?
due to the cell walls
compare animal and plant cytokinesis.
- animal cells: form cleavage furrow, plant cells do not bc of cell wall + high internal pressure
- plant cells: use vesicles for cytokinesis, animal cells do not
describe the purpose of mitotic cell division
- ensures both daughter cells produced when a parent cell divides are genetically identical
- necessary when all of the daughter cells have to be identical
list 4 roles of mitosis
- growth of organisms
- repair/Replacement of tissues
- embryo development
- asexual reproduction
what is the mitotic index?
ratio between number of cells in mitosis and total number of cells
how would you calculate the mitotic index of a sample of dividing cells
- count number of cells in sample and number of cells in mitosis
- divide number of cells in mitosis by total number of cells
how would you calculate how many cells have been produced during mitosis from one cell given the number of cell cycles that have taken place.
2(^x) where x is the number of cell cycles
explain how to calculate length of time each stage in cell cycle takes given a sample of cells undergoing mitotic cell division and total duration of the cell cycle.
- calculate mitotic index
- multiply that by total duration - calculates amount of time mitosis takes up in cell cycle
- subtract mitosis time from total cell cycle time to get time in interphase
