cellular division Flashcards
what is mitosis
a type of nuclear division giving rise to genetically identical cells in which the chromosome number is maintained
in what cells does mitosis occur
somatic cells
what is mitosis important for
- asexual reproduction
- growth in multicellular organisms
- repair of damaged tissues
phases of mitosis
prophase, metaphase, anaphase, telophase
what happens during prophase
- chromatin condenses by supercoiling into chromosomes
- nucleolus disappears, and nuclear envelope breaks down
- (in animals) centrioles replicate to form centrosomes that form spindle fibres
what happens during metaphase
- centrosomes move to opposite ends of the cell
- microtubules of the cytoplasm start to form into a spindle
- each pair of sister chromatids is attached to a microtubule of the spindle and is arranged at the equator of the spindle
what happens during anaphase
- centromeres separate, spindle fibres shorten
- sister chromatids are pulled by centromeres to opposite poles
what happens during telophase
- nuclear envelope reforms around both groups of chromosomes at opposite ends of the cell
- chromosomes uncoil to become chromatin again
- nucleolus reforms in each nucleus
what happens during telophase
- nuclear envelope reforms around both groups of chromosomes at opposite ends of the cell
- chromosomes uncoil to become chromatin again
- nucleolus reforms in each nucleus
what is cytokinesis
cytoplasm division
cytokinesis in animal cells
- cleavage furrow appears near the old metaphase plate
- cleavage furrow deepens until the cell is pinched into 2, producing completely separated cells
cytokinesis in plant cells
- golgi apparatus forms vesicles of new cell wall materials, which collect along the line of the equator of the spindle
- vesicles merge, forming new cell surface membranes and cellulose cell walls between the cells
what is cancer
disease of uncontrolled cell division that may develop when carcinogens cause mutations in genes that control the cell cycle
what are carcinogens
- agents that may cause cancer
- highly likely to cause damage to DNA molecules, resulting in mutation. accumulation of multiple mutations results in uncontrolled cell division
- e.g. x-rays, tobacco, asbestos, UV light
development of cancer
- normally dividing cells subjected to prolonged exposure to carcinogens develop / accumulate mutations
- mutated cells undergo repeated, rapid mitosis and do not respond to signals from other cells
- malignant tumour cells secrete signals triggering the growth of blood and lymph vessels to serve the tumour cells at the expense of other tissues (angiogensis) cells may be spread to other locations (metastasis)
what is a haploid cell
cell containing one set of chromosomes
what is a diploid cell
cell containing 2 sets of chromosomes, 1 from each parent
why must gametes be haploid
allows for a diploid zygote to be formed; keeps the chromosome number from doubling each time sexual reproduction occurs
homologous pair meaning
- one chromosome from male parent, one from female parent
- chromosomes are of same shape, same size, and contain the same sequence of genes
what is meiosis
type of nuclear division that gives rise to genetically dissimilar cells in which the chromosome number is halved due to the separation of homologous chromosomes
phases of meiosis
prophase I and II
metaphase I and II
anaphase I and II
telophase I and II
what happens during prophase I
- homologous chromosomes pair up in a process called synapsis
- non-sister chromatids come into contact with each other at the chiasma
- crossing over between non-sister chromatids results in new combinations of alleles on the chromosomes, mixing paternal characteristics in offspring
what happens during metaphase I
- spindle forms
- homologous pairs become attached to individual microtubules by their centromeres
- homologous pairs are arranged at the equator of the spindle
what happens during anaphase I
- chromosomes of each homologous pair move to opposite poles of the spindle (chromatids remain attached by their centromeres)
