cell biology

• Evidence for Davson-Danielli:

  • electron micrographs showed dark layer outside the bilayer
  • suggested this was a layer of proteins
  • phospholipid bilayer model
  • was INCORRECT
• evidence for Singer and Nicholson:

  • free etched micrographs- membrane split had lumps and depressions showing transmembrane proteins
  • Biochemical analysis- proteins found to be globular and different size, and were also partially hydrophobic so would be found within the bilayer
  • Fluorescent tagging of membrane proteins of different cells
• osmosis is the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration
• hypertonic: a solution with high solutes and few free water molecules
• hypotonic: solution with low solutes and lots of free water molecules
• isotonic: solution with same solute and water concentration
• Endocytosis: The process of engulfing material from the extracellular environment into the cell.
• exocytosis: releases materials synthesised by the cell
• meiosis: a type of cell division that produces four haploid daughter cells from one diploid parent cell
• mitosis: the process of cell division that results in two identical daughter cells
• Two main phases of the cell cycle:

  1. interphase
  2. G1 phase- cellular contents duplicated except chromosomes
  3. S phase- replication of all genetic material
  4. G2 phase- Final checks and repairs
  5. cell division
• Mitosis:

  • early prophase
  • spindle microtubules are growing
  • chromosomes become thicker (supercoiling)
• Mitosis:

  • late prophase
  • DNA replication forms two identical chromatids
  • held together by a centromere
  • nuclear envelope breaks down
• Mitosis:

  • metaphase
  • chromosomes align at the equator
  • spindle fibres attached to each centromere from both poles
• Mitosis:

  • Anaphase
  • each centromere divides, pairs of sister chromatids to be pulled to each poles
  • separation of daughter chromosomes
• Mitosis:

  • Early Telophase
  • all chromosomes reach the opposite poles
  • nuclear membrane reforms
  • spindle fibres breakdown
• Mitosis:

  • Late Telophase
  • chromosomes uncoil
  • no longer visible
  • cell starts to divide
• Cytokinesis:

  • plant- new cell wall across the equator with plasma membrane from both sides
  • animal- plasma membrane is pulled inwards until it meets the centre