cell biology

• Cell theory


  Cells are the smallest units of life
• Living organisms


  • Unicellular
  • Multicellular
• unicellular organisms consist of only one cell
• Unicellular organisms


  • Paramecium
  • Chlamydomonas
• Skeletal muscle


  • Made up of muscle fibres
  • Enclosed inside a membrane
  • Much larger than cells
• As a cell gets larger, its surface area to volume ratio gets smaller
• Emergent properties


  Arise from the interaction of the components in a complex system
• Stem cells


  Cells that have the capacity to divide and differentiat- human embryos
• The use of stem cells raises ethical issues
• Therapeutic use of stem cells

  • Improve health and quality of life for patients
  • Source of stem cells is human embryos
• White blood cells


  • Produced in bone marrow- leukemia
• Stargardt's Macular Dystrophy


  • Genetic disease causing loss of vision
  • Treated using embryonic stem cells to develop into retina cells
• differentiation

  organisms entire set of genes is it’s genome. a cell only uses the genes it needs to follow it’s pathway for development
• Binary fission in prokaryotes

  1. Splitting in 2

  2. Bacterial chromosome is replicated so there are 2 identical copies

  3. Copies move to opposite ends of the cell

  4. Cell wall is pulled inwards making the cell pinch to form 2 identical cells
• davison- danielli model

  Bilayer of phospholipids in the centre and layers of protein on either side
• Fluid mosaic model


  • Phosphate head and 2 fatty acid tails
  • Integral and peripheral proteins- glycoproteins
  • Cholesterol in the centre of the phospholipid bilayer
• Phospholipids

  • Hydrophilic and hydrophobic (amphipathic)
  • Phosphate head makes contact with water
• singer nicolson model- globular proteins were present in the centre of the phospholipid bilayer. Proteins can move within the membrane
• Cholesterol is present in the centre of the phospholipid bilayer and restricts movement of phospholipid molecules, reduces fluidity and permeability of membrane
• Diffusion

  Passive movement of particles from a region of high concentration to a region of low concentration
• Simple diffusion


  • Some particles are allowed through the partially permeable membrane
  • Particles move between the phospholipid molecules in the membrane
• Facilitated diffusion

  • Channel proteins are needed
  • Only allow 1 type of sub to pass
• osmosis

  1. passive movement of water molecules from low conc to high conc

  2. across a partially permeable membrane
• Active transport

  • Movement of substances across membranes using energy from ATP
  • Against concentration gradient, from low concentration to high concentration, across a partially permeable membrane, protein pump is used
• Endocytosis

  Small pieces of membrane can be pinched off the plasma membrane to create a vesicle containing material from outside the cell
• Exocytosis

  Vesicles can move to the plasma membrane and fuse with it, releasing the contents of the vesicle outside the cell
• origins of cells

  formed by the division of pre-existing cells
• Symbiosis

  Two organisms living together- smaller is inside a vesicle in the cytoplasm of the larger cell
• Chromatids

  Each chromosome is a double structure - sister chromatids held at one point by a centromere.
• Organisms with long necks were seen in the flasks with short necks, no organisms appeared spontaneously
• Chromosomes

  Eukaryotic DNA molecules have proteins attached, forming chromosomes
• Chromosome condensation in mitosis

  1. Chromosomes become shorter and fatter

  2. Occurs by supercoiling
• Stages of mitosis

  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Chromatids

  DNA replication produces 2 chromatids which contain identical DNA, centromeres divides and sister chromatids separate
• Cytokinesis

  Division of cytoplasm to form 2 cells after mitosis
• Mitotic index

  Ratio between number of cells in mitosis and total number of cells
• Cell cycle

  Sequence of events between cell division
• Cell cycle

  1. Interphase

  2. Cell division
• Cyclins

  Group of proteins that ensure the cell moves to the next stage at the correct time
• Cyclins

  Bind to enzymes called cyclin-dependent kinases which become active and attach phosphate groups to other proteins