Cell division

• The role of mitosis and the cell cycle is to produce identical daughter cells for growth and asexual reproduction.
• The three stages of the cell cycle are interphase, cell division and, cytokinises
• Mitosis produces 2 daughter cells while meiosis produces 4.
• Meiosis produces genetically different cells through the crossing over of chromatids and independent assortment of chromosomes.
• Crossing over of chromatids occurs when pairs of chromosomes line up and exchange some of their genetic material.
• The main role of meiosis is the production of haploid gametes that have half the number of chromosomes.
• Independent assortment of chromosomes means there are various combinations of chromosome arrangement.
• Daughter cells in mitosis have the same number of chromosomes as parent cell, while meiosis halves the number.
• Mitosis produces genetically identical cells whereas meiosis doesn’t.
• The main role of meiosis is to produce genetically diverse offspring.
• During the 'telophase' stage of mitosis, the nuclear envelope reforms, chromosomes decondense, and spindle fibres disappear.
• During the 'metaphase' stage of mitosis, chromosomes align along the equator of the cell.
• The 'cytokinesis' stage of the cell cycle involves the division of the cytoplasm and the production of two genetically identical daughter cells.
• During the 'anaphase' stage of mitosis, centromeres divide and sister chromatids move to opposite poles.
• During the 'prophase' stage of mitosis, spindle fibres appear and chromosomes condense.
• The four stages of mitosis are Prophase, Metaphase, Anaphase, and Telophase.
• The cell grows and prepares to divide by replicating organelles and condensing chromosomes during the 'interphase' stage of the cell cycle.
• Chromosomes are made up of DNA and proteins called histones
• the DNAs double helix structure runs through the length of the chromatids small sections of this are called genes
• a chromosome only has the x shape when the chromatin condenses
• the centromere maintains the structure of the chromatids and chromosomes
• the ploidy level of an organism is the number of complete chromosome pairs in an organism
• a polyploid is a organism with more than 2 complete sets of chromosomes
• haploid cells have one set of chromosomes, diploid cells have two sets of chromosomes
• mitosis is a type of cell division in which two daughter cells have the same number of chromosomes and are genetically identical to each other and the parent cell
• interphase is the longest stage of the cell cycle
• in interphase …

  • Cell grows and organelles replicate
  • DNA replicates
  • ATP synthesises histones and enzymes
  • chromatin is dispersed throughout the nucleoplasm
• the full cell cycle in a mammalian cell is 24 hours almost 22 of which is interphases
• a human liver cell takes a whole year to under go the full cell cycle
• the cell cycle is 3 stages

  • Interphase - growth
  • mitosis - cell division
  • cytokinesis - division of cytoplasm
• mitosis is 4 stages

  1. Prophase
  2. metaphase
  3. anaphase
  4. telophase
• the goal of mitosis is to produce 2 genetically identical daughter cells
• in prophase…

  • Chromosomes condense coils get shorter
  • centrioles separate to their opposite poles
  • protein microtubials form from the centrioles making the spindle fibres
  • nuclear envelope breaks down
  • Nucleolus disappears
• in metaphase…

  • Chromosomes line up at the equator of the cell
  • if cell was viewed from the pole chromosomes look spread out
• in anaphase..

  • Spindle fibre shorten
  • centromeres separate
  • sister chromatids separated and pulled towards the poles
• the spindle fibres are able to pull and shorten well because of the removal of the tubulin protein that makes up the micro tubules that make up the spindle
• in telophase…

  • chromosomes uncoil and lengthen
  • spindle fibres break down
  • nuclear envelope reforms
  • nucleolus reappears
• in cytokinesis in animals…

  • Cytokinesis occurs by the constriction of cytoplasm at the equator of the parent cell
  • it forces the cell into 2 from the outside inwards
• cytokinesis in plants…..

  • Occurs when droplets of the cell walls line up at the equator and form a cell plate across the equator of the parent cell
  • forces cell in 2 from the inside out
  • joins a new cell wall
• One significance of mitosis is that it maintains the chromosome number of a cell. this is because this is because the daughter cells are genetically identical to the parent cell. This insures genetic stability.