cell & nuclear division Flashcards
what are the 3 subphases in interphase?
G1, S & G2
describe what happens during G1 phase of interphase.
G1 phase begins after cytokinesis of the previous cell division. the cell is small in size and low in ATP.
so during G1 phase, cells increase in size and acquire ATP.
intensive cellular gene expression and synthesis of appropriate organelles and proteins occur.
describe what happens during S phase of interphase
each DNA molecule undergoes semi-conservative DNA replication, producing 2 identical DNA molecules
histone proteins are synthesised and associate with each DNA molecule
after DNA has replicated, they remain fully extended and uncoiled
describe what happens during G2 phase of interphase
last stage before nuclear division
since DNA replication is an energy-consuming process, the cell undergoes a second growth and energy acquisition stage
cells increase in size and acquire ATP
further synthesis of appropriate organelles and proteins occur
centrioles replicate and mitotic spindle begins to form
what is mitosis?
mitosis involves the nuclear division of one nucleus into 2 genetically identical nuclei. after cytokinesis, it produces 2 daughter cells that are genetically identical to each other and the parent cell.
mitosis occurs in somatic cells, allowing daughter nuclei to receive precisely the same number of chromosomes as the parental nucleus, maintaining the diploid condition from one generation to the next
what are the 4 stages of mitosis?
prophase
metaphase
anaphase
telophase
describe what happens during prophase of mitosis.
- nuclear envelope disintegrates
- nucleolus gradually disappears
- chromatin becomes more tightly coiled and condense into discrete chromosomes
- centriole pairs migrate to opposite poles of the cell (only in animal cells, plan cells don’t have centrioles)
- the spindle fibre that began to form in G2 continues to develop
describe what happens during metaphase of mitosis
- centriole pairs are positioned at opposite poles of the cell
- shortening and thickening of chromosomes is at its maximum
- 2 sister chromatids are joined at the centromeres of each chromosome. each of the 2 sister chromatids of a replicated chromosome has a kinetochore at the centromere
- kinetochore microtubules attach to the kinetochores at the centromeres of chromosomes
- chromosomes migrate and align singly at the metaphase/equatorial plate. they are pulled to the metaphase plate by kinetochore microtubules
NO pairing of homologous chromosomes
some drugs like colchicine interfere with spindle function and can arrest cells at metaphase
describe what happens during anaphase of mitosis
- centromeres divide and sister chromatids are separated
- once the centromeres of sister chromatids are separated, chromatids are known as daughter chromosomes
- daughter chromosomes are pulled to opposite poles of the cell as their kinetochore microtubules shorten
- as kinetochore microtubules are attached at the kinetochore, chromosomes move with the centromere leading towards the poles of the cell, so separated daughter chromosomes are pulled along behind the centromeres, producing a V shape pattern
- poles of the cell move farther apart as polar microtubules slide past each other, elongating the cell
- special motor proteins are involved in the rapid and abrupt movement of chromosomes towards the poles of the cell during anaphase
- at the end of anaphase, the 2 poles of the cell have equal and complete sets of chromosomes
describe what happens during telophase of mitosis
- chromosomes decondense
- chromatin forms by uncoiling
- the nucleolus and nuclear envelope reform
- microtubules dissassemble, and a pair of centrioles end up in each daughter cell
how is the integrity of genetic information in daughter cells ensured during mitosis?
during interphase, semi-conservative DNA replication occurs, using the parental DNA molecule as the template for making genetically identical copies of daughter DNA molecule. this also occurs before the disintegration of the nuclear membrane and before the distribution of genetic material to the 2 daughter cells.
how is entanglement of chromatin & DNA breakage prevented during mitosis?
during prophase, long, thin chromatin is coiled into condensed, thick and discrete chromosomes to prevent entanglement of chromatin and DNA breakage during the separation of genetic material.
this ensures equal distribution of nuclear DNA to daughter cells
how is it ensured that each daughter cell has the complete diploid set of DNA during mitosis?
during metaphase, chromosomes align singly at the metaphase/equatorial plate, and no pairing of homologous chromosomes occur
during anaphase, sister chromatids are separated towards opposite poles of the cell by shortening of kinetochore microtubules
during telophase, daughter chromosomes reach the opposite poles of the cell before cytokinesis.
this ensures that each daughter cell will have the complete diploid set of DNA
what is cytokinesis?
cytokinesis is the division of the cytoplasm to produce 2 daughter cells
cell organelles become evenly distributed towards the 2 poles of the cell
describe cytokinesis in animal cells.
- cytokinesis involves the formation of a cleavage furrow, which pinches the cell in 2
- it first forms as a shallow groove in the cell surface near the metaphase plate
- on the cytoplasmic side of the furrow is a contractile ring of microfilament. the ring of microfilaments contracts, the cleavage furrow deepens until the parent cell pinches into 2 daughter cells, each with a complete nucleus and share of cytosol, organelles and other subcellular structures