cell division Flashcards
Cell division
nuclear division (meiosis and mitosis) and cytoplasmic division (cytokenesis) must occur
Interphase
stage between cell divisions
G1 phase (growth phase)
Duplication of the chromosome (DNA replication)
duplication of centromeres (S phase - synthesis phase)
G2 phase (growth phase)
G0 (sometimes)
Chromosomes not visible
Growth phase
growth and reproduction of organelles as cell prepares to divide
G0
Undergoing an extended G1 phase but are not preparing to replicate their DNA and divide.
cells in stage are withdrawn from active cell cycle and can only re-enter under some circumstances
centromere
Contains 2 centrioles
becomes visible in S phase
Produces spindle fibre
S phase
Chromatin duplicates and the cell doubles its amount of genetic material
cytokenesis
Occurs after mitosis
forms two seperate diploid daughter cells
Division and separation of the cytoplasm to create the new daughter cells
Mitosis
Interphase
prophase
Metaphase
anaphase
Telophase
prophase (Mitosis)
Chromatid threads condense to form chromosomes
nuclear membrane disintegrate and nucleotides disappears
Spindle fibre forms and attaches to each chromosome at centromere
centromeres move towards opposite poles of the cell
Metaphase (Mitosis)
Chromosomes move to centre of the cell and live up along the equator of the cell. Equator referred to as the metaphase plate.
centromeres of chromosomes are aligned on the equator
The centrioles are located at opposite poles of the cell
Anaphase (mitosis)
Spindle microtubules shorten and pull on the centromeres
spindle microtubules pull sister chromatids pull to opposite poles of the cell
Sister chromatids now referred to as chromosomes
at the end of phase, each pole has complete identical set of maternal and paternal chromosomes
Telophase (mitosis)
chromosome decompress to form chromatin, no longer visible under microscope
Two new nuclear membranes form for each cell
Nucleoli reappear, spindle fibre apparatus disappears.
Cell elongates and cleavage furrow forms to become ready for cytokinesis
cytokinesis in plants
Cytoplasm of plant cells divide with the formation of a structure called a cell plate.
cell plate - formed when parts of cell wall fuse wt spindle fibre, cellulose is deposited there, forming a wall that divides the parent cell.
Cytokinesis in animals
cytoplasm divides by process known as cleavage.
Cell membrane around the middle of the cell draws together to form a cleavage furrow.
cleavage furrow continues to develop until the cell membrane eventually meets at a point, cell then splits
Binary fission
reproduction of prokaryotes as they lack nucleus.
Process of asexual reproduction whereby a prokaryotic cell divides into two identical daughter cells.
process includes: DNA replication, chromosome segregation, cytokinesis
Mutation is only cause of variation in prokaryotes. Process much quicker compared to meiosis and mitosis, therefore higher rates of mutation.
binary fission steps
Prokaryote replicates their single DNA strand, signalling beginning of binary fission.
original and replicate chromosomes attach to the cell membrane and are pulled to seperate poles as the cell elongates.
Cleavage furrow develops forming new cell wall.
New cell wall fully develops
two cells seperate (cytokinesis), chromosomes become tightly coiled again.
Continuous process.
meiosis
Production of gametes
plants - gametes are pollen and ovules
Daughter cells have half of parent cell DNA
two divisions of nucleus take place - 1 DNA replication
Called a reduction division
Bivalent - during Meiosis 1, homologous chromosomes pair and physically connect. Synapsis is what causes them to physically connect.
Crossing over
exchange of genetic material between maternal and paternal homologous chromosomes
Recombination of genes
happens through: crossing over, independent assortment and random fertilisation
Random assortment
independent assortment
Assortment of one pair of chromosomes between daughter cells is independent of that of another pair.
Meiosis
Prophase 1
Metaphase 1
Telophase 1
Cytokinesis 1
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2
Cytokinesis 2
Prophase 1
Chromatin condenses forming chromosomes
crossing over occurs
Nuclear membrane disintegrates and nucleolus disappears
spindle fibre attaches to chromosomes at centromere.
Centromeres move to opposite poles
Metaphase 1
Chromosomes line up along metaphase plate (equator) in pairs
lining up of chromosomes at equator is independent assortment
Anaphase 1
Spindle fibres shorten, pulling on centromere of each chromosome.
one of each pair moves to each end of the cell
