Mitosis/Meiosis Flashcards
What is mitosis?
Nuclear division stage in mitosis phase of cell cycle
What does Mitosis result in?
Ensures that both daughter cells produced when a parent cell divides are genetically identical and each new cell will have an exact copy of the DNA present in the parent cell and the same number of chromosomes
Why is mitosis necessary?
Whenever all daughter cells have to be identical
GROWTH
REPLACEMENT AND REPAIR OF TISSUES
ASEXUAL REPRODUCTION - genetic,a,g identical offspring from one parent in organisms such as plants fungi etc (Amoeba)
How do bacteria reproduce?
They do not have w nucleus so they reproduce asexually through binary fission
When is DNA in nucleus replicated?
During Interphase ; each chromosome is converted into two identical DNA chromatids (two identical copies of DNA held together at a centromere)
What are centromeres?
They are where the two chromatids are joined - have to keep them together so they can be manoeuvred precisely and segregated equally into the two new daughter cells
After replication what do we have in relation to chromosomes and chromatids?
Two chromatids per chromosome - unlike before where there was 1 chromatid per chromosome
4 stages of mitosis
Prophase
(Prometaphase) Metaphase
Anaphase
Telophase
How can the dividing cells be seen during an experiment?
Through a light microscope - growing root tips of plants (meristems where there are stem undifferentiated cells) ; root tips can be treated with a chemical to allow the cells to be separated and they can then be squashed to form a single layer of cells and stains that bind to DNA are used to make the chromosomes more visible
Prophase
ChromatiN fibres (proteins) condense and coil to form chromosomes that will take up stain to become visible under the light microscope ; nucleoplasm disappears and nuclear membrane begins to break down Microtubules form spindle structures linking the poles of the cell which are necessary to move the chromosomes Two centrioles migrate to opposite poles that help in formation of spindle Spindle fibres attach to specific areas on centromere and move chromosomes (2 sister chromatids) to the centre of the cell and nuclear envelope has totally disintegrated
Metaphase
Chromosomes are moved by the spindle fibres to form a plane in the centre of the cell called the metaphase plate (mitotic spindle from opposite poles with two centrioles each side)
Anaphase
Centromeres holding together the sister chromatids divide and the chromatids are separated and pulled to opposite poles by shortening spindle fibres ; the V shaped chromatids are dragged to poles by the centromeres through liquid cytosol
Telophase
Chromatids have reached the poles and are now called chromosomes - two new sets of chromosomes assemble at each pole and the nuclear envelope reforms around them ; chromosomes start to uncoil and nucleoli is formed and cell division (CYTOKINESIS) begins
Cell division nuclear division?
Cell div - cytokinesis ; 2 separate cells
Nuclear div - mitosis
How does cytokinesis work in animal cells?
A cleavage furrow forms around the middle of the cell and the cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle forming two cells
