module 2 (cell structure)

• Resolution


  The minimum distance between two objects in which they can still be viewed as separate objects
• Wavelength


  Determines the resolution in a light microscope and electron microscope
• Magnification


  How many times larger the image is compared to the object
• Types of microscope


  • Optical microscope
  • Transmission electron microscope
  • Scanning electron microscope
  • Laser scanning confocal microscope
• Dry mounts


  Thin slices or whole specimens are viewed with just the coverslip placed on top
• Wet mounts


  Water is added to the specimen before lowering the coverslip with a mounted needle to prevent air bubbles from forming
• Squash slides


  Wet mounts where the coverslip is pushed down to squash the sample
• Smear slides


  Ensures a thin layer is obtained so that light can pass through
• Eye piece graticule


  A small piece of glass with a measurement scale etched on its surface that fits inside a microscope eyepiece
• Calibrating the eyepiece graticule

  1. Line up the stage micrometer and eyepiece graticule whilst looking through the eyepiece

  2. Count how many divisions on the eyepiece graticule fit into one division on the micrometer scale

  3. Each division on the micrometer is 10μm, so this can be used to calculate what one division on the eyepiece graticule is at that current magnification
• Differential staining


  A technique involving many different chemical stains being used to stain different parts of a cell in different colours
• Gram staining


  A common use of differential staining that allows different bacteria to be visualised using two different stains - crystal violet and safranin
• Features of scientific drawings

  • Draw in pencil
  • Title the diagram to indicate what the specimen is
  • State the magnification that you are drawing it from
  • Annotate cell components, cells and sections of tissue visible
  • Do not scetch- only use solid lines that do not overlap
  • Do not colour in or shade
• How does a TEM work?

  A beam of electrons pass across the sample used to create an image, focused using electromagnets
• Evaluation of TEMs


  • Highest resolving power
  • High magnification
  • Extremely thin specimens required
  • Complex staining method
  • Specimen must be dead
  • Vacuum required
• How does a SEM work?

  A beam of electrons passes through the sample used to create an image, focused using electromagnets in a vacuum
• Evaluation of SEMs


  • High resolving power
  • High magnification
  • Thick specimens unusable
  • Complex staining method
  • Specimen must be dead
  • Vacuum required
• How does a laser scanning confocal microscope work?

  A type of fluorescent microscope, the image is created using a very high light intensity to illuminate the specimen stained with a fluorescent dye, and the microscope scans the specimen point-by-point using a focused laser beam
• Evaluation of laser scanning confocal microscope

  • High resolution
  • High depth selectivity
  • Can view tiny structures (e.g. embryos) in detail
• Plasma membrane structure


  Phospholipid bilayer with embedded intrinsic and extrinsic proteins
• Nucleus structure


  Surrounded by a double membrane nuclear envelope with nuclear pores, contains chromosomes with protein bound, linear DNA, and a nucleolus to synthesise ribosomes
• Nucleus function


  Site of transcription and pre-mRNA splicing, site of DNA replication, nucleolus makes ribosomes, nuclear pore allows movement of substances to/from cytoplasm
• Plasma membrane function


  Maintain structural integrity and act as a barrier, controlling passage of substances in and out of the cell
• Cilia structure


  Hair-like projections out of cells, can be mobile or stationary

  
• Cilia function


  Mobile cilia help move substances in a sweeping motion, stationary cilia are important in sensory organs, such as the nose
• Flagella structure


  Whip-like structure
• Flagella function


  For mobility, and sometimes as a sensory organelle for chemical stimuli
• Mitochondria structure


  Double membrane with inner membrane folded into cristae, fluid-filled centre called matrix, 70S ribosomes in matrix, small, circular DNA, enzymes in matrix
• Mitochondria function


  Site of aerobic respiration, ATP production
• Centriole structure


  Made of microtubules and occur in pairs to form a centrosome
• Centriole function


  Involved in the production of spindle fibre and organisation of chromosomes in cell division
• Golgi apparatus structure


  Stacks of membranes creating flattened sacs called cistern, surrounded by small, round and hollow vesicles
• Golgi apparatus function


  Proteins and lipids are modified here, carbohydrates can be added to proteins to form glycoproteins, finished products are transported in the golgi vesicles
• Lysosome structure


  Formed when the golgi apparatus contains hydrolytic enzymes
• Lysosome function


  A type of golgi vesicle that releases lysozymes to hydrolyse pathogens/ cell waste products
• Cytoskeleton structure


  A network of fibres found within the cytoplasm all over a cell, consists of microfilaments, microtubules and intermediate fibres
• Cytoskeleton function


  Provides mechanical strength to cells, and helps to maintain the shape and stability of a cell
• Ribosome structure


  Small granules in cells made up of protein and rRNA, ribosomes are made up of a small and large subunit (80S size in eukaryotes)
• Ribosome function


  Site of translation in protein synthesis
• RER structure


  System of membranes with bound ribosomes that is often continuous with the nucleus