2- eukaryotic cell cycle and division Flashcards
cell cycle definition
a regulated process in which cells divide into two identical daughter cells
three stages of the cell cycle
- interphase: G1, S and G2
- mitosis: prophase, metaphase, anaphase and telophase
- cytokinesis
chromatin
- DNA packaged with histones
- DNA + histones -> nucleosomes -> chromatin -> chromosomes
homologous chromosome
- pair of chromosomes with the same sequence of genes, but different alleles
- one is inherited from each parent
chromatid
one of two identical halves of a chromosome replicated for cell division
sister chromatids
two identical halves of a chromosome, joined at the centromere
centromere
it is the restricted region of a chromosome, linking a pair of sister chromatids
centrosome
it consists of two centrioles, arranged at right angles to each other
purpose of the cell cycle
- growth of multicellular organisms
- replacement of cells and repair of tissues
- asexual reproduction
purpose of meiosis
- production of haploid gametes
- maintenance of chromosome numbers
mitotic index
the amount of cell division occurring in a tissue is quantified using the mitotic index
mitotic index =
number of cells containing visible chromosomes/ total cells in field of view
cell counts
the number of cells in each stage of mitosis
what does the cell count show
the relative duration of each stage in the cell cycle. the longer a phase, the more cells are likely to be going through the phase
steps in the cell cycle
interphase (gap 1 -> synthesis -> gap 2) -> mitosis (prophase -> metaphase -> anaphase -> telophase) -> cytokinesis
interphase- gap 1
- cells increase in size
- transcription occurs
- organelles replicate
- biosynthesis occurs: the generation of natural products through enzymatic reactions
interphase- synthesis
- DNA replicates by semi- conservative replication
- each chromosome now consists of 2 sister chromatids
- the amount of DNA has doubled
- this is rapid because exposed DNA base pairs are more susceptible to mutations
interphase- gap 2
- cells continue to increase in size and prepare for mitosis
- DNA is checked for errors
- energy stores (ATP content) are increased
mitosis- prophase
- chromosomes supercoil
- the nuclear membrane breaks down, and the nucleolus disappears
- centrioles divide into two and move to opposite ends of the cell
mitosis- metaphase
- chromosomes align at the metaphase plate at the equator of the cell
- chromosomes are joined to spindle via the centromere
mitosis- anaphase
- centromeres divide
- spindle fibres shorten, and split the centromere to separate sister chromatids
- motor proteins walking along tubular
mitosis- telophase
- chromosomes detach from spindle fibres and start to uncoil
- nuclear envelopes begin to form around each group of chromosomes
- there are now two nuclei
- spindle fibres break down and the nucleolus reforms
cytokinesis- animal cells
- the plasma membrane is pulled inwards by the cytoskeleton
- it forms a cleavage furrow in the middle of the cell
cytokinesis- plant cells
- vesicles from the golgi line up where the metaphase plate was to form a cell plate
- vesicles secrete a layer of calcium pectate called the middle lamella
- onto this, a primary cell wall made of cellulose microfibrils is laid down
- then a secondary cell wall at right angles is deposited
- the cell wall may be impregnated with lignin
meiosis results in
genetic variation
what are the two ways genetic variation can be achieved
- crossing over (meiosis 1, prophase 1)
- independent assortment (meiosis 1, metaphase 1)
crossing over
the exchange of sections of DNA between homologous chromosomes
independant assortment
there are various combinations of maternal and paternal chromosome arrangement
chromosome mutations are
changes to the number or structure of chromosomes
types of chromosome mutations
- translocations
- duplications
- deletions
- inversions
- nondisjunctions
translocations
part of one chromosome breaks off and reattaches to a different one
deletions
a section of chromosome is removed, resulting in a loss of a large number of genes
inversions
a part of a chromosome flips it’s orientation
nondisjunctions
homologous chromosomes or sister chromatids fail to separate
nondisjunctions can result in
- polysomy
- monosomy
polysomy
the presence of extra copies of chromosomes
example of polysomy
down’s syndrome- there are 3 copies of chromosome 21
monosomy
the absence of one member of a pair of chromosomes
monosomy example
turner’s syndrome- monosomy of the sex chromosome, where only one sex chromosome is present in a cell (X chromosome)
