Topic 1 - Cell Biology

• Cell theory


  • All living organisms are made up of one or more cells
  • Cells are the basic functional unit in living organisms
  • New cells are produced from pre-existing cells
• Cells vary in size and shape but all are surrounded by a membrane, contain genetic material, and have chemical reactions occurring within the cell that are catalysed by enzymes
• Atypical examples that question the cell theory

  • Striated muscle fibres
  • Aseptate fungal hyphae
  • Giant alga (Acetabularia)

  
• Functions of life


  • Metabolism
  • Reproduction
  • Homeostasis
  • Growth
  • Response
  • Excretion
  • Nutrition

  
• Surface area to volume ratio

  • As organisms increase in size, their SA:V ratio decreases
  • This limits the rate of exchange of substances and metabolic reactions
• Emergent properties


  Multicellular organisms can undertake functions that unicellular organisms cannot, due to the organisation and interaction of individual cells
• Levels of organisation in multicellular organisms

  • Cells
  • Tissues
  • Organs
  • Organ systems
  • Organism
• Cell differentiation


  • Specialisation of cells enables them to function more efficiently by developing specific adaptations for their role
  • Specialised cells have the same genome but express different genes
• Once certain genes are expressed, the specialisation of the cell is usually fixed so the cell cannot adapt to a new function
• Stem cell


  A cell that can divide (by mitosis) an unlimited number of times
• Potency


  The ability of stem cells to differentiate into more specialised cell types

  
• Types of potency


  • Totipotency
  • Pluripotency
  • Multipotency
  • Unipotency
• Totipotent stem cells


  Can differentiate into any cell type found in an embryo, as well as extra-embryonic cells (the cells that make up the placenta)

  
• Pluripotent stem cells


  Embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells

  
• Multipotent stem cells


  Adult stem cells that can differentiate into closely related cell types
• Unipotent stem cells


  Adult cells that can only differentiate into their own lineage

  
• Totipotent cells have the highest potency and can differentiate into any type of cell. Unipotent cells have the lowest potency, only being able to divide into one cell type.
• The two key properties of stem cells are that they can self-renew (capacity to divide) and can differentiate
• Therapeutic uses of stem cells

  • Embryonic stem cells
  • Cord blood stem cells
  • Adult stem cells
• Cord blood stem cells

  Multipotent and have limited capacity to differentiate into different cell types
• Adult stem cells


  Difficult to obtain, multipotent and have limited capacity to differentiate into different cell types, risk of rejection if donated from one person to another
• Optical (light) microscopes allow for tissues, cells and organelles to be seen and studied
• Key components of an optical (light) microscope

  • Eyepiece lens
  • Objective lenses
  • Stage
  • Light source
  • Coarse and fine focus
• Magnification


  How many times bigger the image is compared to the actual size of the specimen
• Calculating magnification


  1. Magnification = Size of image / Actual size of specimen

  2. Use a scale bar to measure the size of the image and the actual size on the scale bar
• Measurements are typically in micrometres (μm) or nanometres (nm)
• Miller and Urey found traces of simple organic molecules including amino acids in their mixture
• Endosymbiosis


  • If the relationship is beneficial to both organisms the engulfed organism is not digested
  • For endosymbiosis to occur one organism must have engulfed the other by the process of endocytosis
• Endosymbiotic theory


  1. Ancestral prokaryote cells evolved into ancestral heterotrophic and autotrophic cells

  2. Heterotrophic cells: Ancestral prokaryote cells developed folds in their membrane, a larger anaerobically respiring prokaryote engulfed a smaller aerobically respiring prokaryote

  3. Autotrophic cells: Heterotrophic eukaryotic cell engulfed a smaller photosynthetic prokaryote
• The endosymbiotic theory is used to explain the origin of eukaryotic cells
• Evidence to support the endosymbiotic theory

  • Mitochondria and chloroplasts have in common with prokaryotes: Reproduce by binary fission, Contain their own circular, non-membrane bound DNA, Transcribe mRNA from their DNA, Have 70S ribosomes to synthesise their own proteins, Have double membranes
• Prokaryotic cell


  Simplest cell structure, first organisms to evolve on Earth
• Domains of prokaryotes


  • Bacteria or Eubacteria
  • Archaebacteria or Archaea
• Prokaryotic cells


  • Small, ranging from 0.1µm to 5.0µm
  • Lack a nucleus
  • Cytoplasm not divided into compartments, lack membrane-bound organelles (except for ribosomes)
  • Prokaryotic ribosomes are 70S
  • Have a cell wall containing murein/peptidoglycan
  • May have plasmids, capsules, flagella, pili

  
• Binary fission


  Parent cell splits into two daughter cells, chromosome replicates, cell elongates, cross wall forms, two daughter cells formed
• Eukaryotic cells have a more complex ultrastructure than prokaryotic cells
• Eukaryotic cells


  • Cytoplasm divided into membrane-bound compartments called organelles
  • Have a nucleus
  • Animal cells contain centrioles and microvilli, plant cells have a cellulose cell wall, large permanent vacuoles and chloroplasts
• Structural adaptations of specialised eukaryotic cells


  • Shape of the cell
  • Organelles the cell contains (or doesn't contain)
• Plasma membrane


  Controls the exchange of materials between the internal cell environment and the external environment
• Nucleus


  Contains chromatin (DNA and histone proteins), separated from cytoplasm by nuclear envelope with pores