Organelles & Microscopes

Eukaryotic cells
1. Animal Cells
  1. Centrioles
    1. made of protein fibres (microtubules), they form the SPINDLE FIBRES for cell division. which then move chromosomes around
    2. Not found in plants
2. Plant Cells
  1. 1. Plants have: +cellulose cell wall +Vacuole +Chloroplast +No Centrioles
      1. Leaf > Leaf cell > Mesophyll Cell > Chloroplast > Thylakoid
        Thylakoids absorbs light for photosynthesis
        Stroma is filled with fluid and starch grains
        Chloroplasts have a double membrane, inner layer not folded but as disks
        adaptions of chloroplasts for light harvesting: +Thylakoids have large SA for attachments of chlorophyll molecules +Chloroplasts have DNA and ribosomes so can quickly make proteins +Chloroplasts have oil droplets for making more phospholipid membrane
    2. Cell Wall
      1. Cell Wall is made of cellulose (a complex carbohydrate ((polysaccharide)) which is freely permeable
      2. The cell wall provides strength as cellulose fibres are strong
      3. Contents of cell press against cell wall = cell is rigid, supports whole plant- stops it wilting
        Vacuole has cell sap which then pushes contents against cell wall
3. 'Has a nucleus'
4. Nucleus
  1. The interior is called - nucleoplasm, it contains the: nucleolus is a region of chromatin: a DNA/Protein complex containing the genes and involved in making ribosomes and RNA
  2. Nuclear envelope, has a double membrane with nuclear pores (allows communication with cytoplasm) so mRNA can leave the nucleus to join with ribosomes.
5. Ribosomes
  1. Small structures found all over the cell, but mostly in endoplasmic reticulum, made up of RNA (no plasma membrane)
  2. Carry out protein synthesis. 70s - Prokaryotic (smaller) 80s - Eukaryotic cell
6. Endoplasmic Reticulum
  1. Rough Endoplasmic Reticulum: Encrusted with ribosomes, RER transports proteins to Golgi Body
  2. Smooth Endoplamsic Reticulum: Site of production, transport of lipids/steroids
7. Golgi Body
  1. Proteins and Lipids get modified and packaged here into glycoproteins and glycolipids, carbohydrate added for exocytosis
  2. Produces vesicles to transport glycolipids and glycoproteins to cell membrane for exocytosis
  3. Produces lysosomes, contain digestive enzymes (lytic), digest pathogens and unwanted organelles , used in white blood cell and sperm cells to digest egg material
8. Mitochondria
  1. site of aerobic respiration - forms ATP. Have a double membrane: outer and inner, the inner membrane is folded to form cristae space inside is called the matrix (maternal) DNA found here
9. Vesicle and lysosome transport
  1. Cytoskeleton (microtubules) provide a pathway for vesicles to move on. There are two motor types which use ATP:
    1. Dynein
    2. Kinesin
  2. Microtubules can be extended or broken down as required
10. Plasma Membrane
  1. Compartmentalise organelles e.g. mitochondria, isolate enzymes/hormones, provides an attachment site for enzymes/hormones/cell signalling
  2. -selective permeability and transport of substances -Forms concentration gradient
  3. Found surrounding cells/organelles (cell surface membrane)
  4. Phospholipid Bilayer: Two layers of phospholipids,The outer region (phosphate head) is hydrophilic (attracted to water). The inner fatty acid tails are hydrophobic (repel water)
  5. Microvilli
    1. Plasma membranes of animal cells are often highly folded to form Microvilli E.g. intestines: increases SA for faster rate of diffusion
11. Cytoskeleton
  1. A network of protein fibres, which stabilise and support the shape of cell as well as changing the shape, and provide transport within the cell e.g. vesicle and lysosome movement
  2. Microfilaments: made of actin, move against each other allowing cellular movement
  3. Microtubules: made of tubulin, Provide strength, control movement of flagella and cilia
  4. Flagella and Cilia: Nine microtubules arranged in a circle with two in the middle, ATP causes movement of microtubules. ATP made by mitochondria. E.g. sperm cell has a flagella
12. Contains Histone Proteins whcih organise/coil DNA into chromosomes
Extracellular Proteins
1. mRNA made by TRANSCRIPTION in the nucleus, mRNA leaves via nuclear pores in envelope, The mRNA attaches to ribosome on RER. A protein is made in ribosome (TRANSLATION) . Transport vesicle moves protein to Golgi Body, where it is modified into a glycoprotein and packaged into secretory vesicle which moves along the microtubule(s) (cytockeleton) to the cell surface membrane which fuses with the vesicle so secretion occurs by exocytosis.
  1. diagram seprerate
2. Examples of substances secreted: +Enzymes: amylase/lipase/protease +Protein Hormones: insulin/ADH
Prokaryotic
1. 'No Nucleus'
2. Contains Plasmids: small DNA loops
3. Capsule: outter layer to protect cell
4. Flagella: allows movement
5. Mesosome: aerobic respiration takes placce, ATP formed.
Types of Microscopes
1. When drawing an organelle/cell: ~Use sharp pencil/Plain paper ~Use 50% of space ~Use correct proportions ~Continuous lines ~No shading ~Ruled labelled lines ~Labels outside diagram/Label lines don't cross ~Include a title ~State magnification of image
2. Electron microscope Sampling:
  1. Dehydration -Removing water molecules as it has to be an air tight vacuum
  2. Artefact: Structures produced due to preparation process i.e. dust
  3. Expensive, Large and Fixed, Sample Prep Complex, Sample often distorted
3. 1. Laser Scanning Confocal Microscope
    1. High intensity laser moved across specimen, causing fluorescence from components that have been labelled with dye. Emitted light from specimen filtered through pinhole aperture. only the light from focused place (focal plane) is detected = 3D Image
    2. Can see tracked progress of protein (movement)
    3. Lower resolution than electron
    4. Can use living cells
    5. 3D: Different depths and layers
  2. Transmission Electron Microscope
    1. Use electrons rather than light as electrons have a shorter wavelengths, Uses electromagnets
    2. Due to transmission - samples must be thin and treated with metal (lead) salts
    3. A beam of electrons is transmitted (focused by electromagnets) through specimen then focused to produce an image
    4. TEM held within vacuum= dead specimen
    5. 2D images only (ultrastructure)
    6. Max Magnification = 500,000x
    7. Max Resolution = 0.2nm
  3. Scanning Electron Microsscope
    1. Use electrons rather than light as electrons have a shorter wavelengths, Uses electromagnets
    2. A beam of electrons is sent across the surface, of a specimen and reflected electrons are then collected.
    3. SEM held in a vacuum
    4. Black and white
      1. Colour can be added digitally
    5. No living specimen
    6. samples must be thin and treated with metal (lead) salts
    7. 3D Images: cell surface organelles
    8. Max Magnification= 100,000x
    9. Max Resolution= 0.2nm
      1. Electrons increase resolution as they have much shorter wavelength = Higher Resolution
  4. Light Microscope
    1. Uses a light source (lamp/LED) that passes through specimen, the light is passed through two lenses before reaching the eye
    2. Two Lenses:
      1. Objective Lens: Nearest to specimen, magnification options: 4x 10x 40x 150x
      2. Eyepiece/Ocular Lens; Always 10x magnification
    3. Total magnification: objective Lens x Eye piece lens
    4. Max Magnification= 1500x
    5. Max Resolution = 200nm
    6. Cheap, Portable & Small, sample prep simple, Samples not often distorted
Slide Preparation
1. 1. Dry Mount: Solid specimen cut or whole with cover slip
  2. Wet Mount: Specimen suspended in water or oil, cover slip placed on at an angle to prevent air bubble
  3. Squash slide: Same as wet mount but with a second slide apply pressure to cover slip to squash specimen
  4. Smear Mount: Edge of slide used to smear specimen
Staining Samples
1. Differential Staining
  1. Used to identify: Different cellular components and different cell types
  2. Used to see Gram-Positive (bacteria with thick peptidoglycan cell walls) and Gram-Negative (Bacteria with thin peptidoglycan cell walls)
    1. Gram Positive: Killed by penicillin as it works by breaking cell wall down, as stain caught in world.
    2. Gram Negative not killed by cell wall as cell wall not essential. As stain washes through cell
  3. Acid-Fast Technique
    1. To identify mycobacterium i.e. TB from other bacteria, using Carbol fuchsin dye, which is carried into the cell using a lipid solvent to stain the cell. Then using acid/alcohol wash will remove stains from any bacteria but not mycrobacterium
2. Stain with coloured/fluorescent chemicals that bind to cell organelles
3. +Makes them visible +Allows identification of cells and organelles +Provides a contrast
4. Positive Staining is attracted to -ve charged material in the cytoplasm: cell components stained
  1. Positive Stains: Crystal Violet and Methylene Blue
5. Negative Staining: repelled by -ve cytoplasm, don't enter organelles, stain background
  1. Negative stains: Nigrosin and Congo Red
Units
1. nm - nanometre
  1. x1000
    1. um - micrometre
      1. x1000
        mm millimetre
  2. x1,000,000
2. PRACTICE CONVERSIONS AND STANDARD FORM
Microscope Preparation
1. Fixing: chemicals (e.g. formaldehyde) are used to preserve specimens - in near natural state
2. Sectioning: Specimens are dehydrated with alcohols and then placed in a mould with wax/resin to form a hard block, then thinly sliced.
3. Staining: Specimen treated with coloured chemicals
4. Mounting: Specimen are then secured to a microscope and a cover slide is placed on top
Size of Specimen
1. Eyepiece Graticule = Placed into the eyepiece lens. Used to measure specimen when seen under microscope. Doesn't change size when you change the magnification, needs to be calibrated.
  1. Don't Know what each division is worth
2. Stage Micrometer = A microscope slide with a scale etched into it of a known size e.g. 1mm Goes on the stage of microscope
3. DO PRACTICE QUESTIONS
Equations
1. Magnification = Image Size / Object or Actual Size
2. Total Magnification = Objective lens x ocular lens
Keywords
1. Magnification: Degree to which the size of an image is larger than the object itself
2. Resolution: The ability to see two objects that are close together as seperate objects and see in detail

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Organelles & Microscopes

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	Created by Amy Cornwell about 5 years ago