notes on cell structure

Question 1

magnification + resolution

Answer 1

mag = image size/object size IMO
mag = how much bigger the image is than the specimen
resolution = how well a microscope distinguishes between 2 points that are close together

Question 2

Light microscope

Answer 2

1) use light
2) max resolution = 0.2micrometers, used for whole cells/tissues
3) max useful mag = x1500

staining

1) use of dye(methylene blue=DNA/eosin=cell cytoplasm)
2) as stain is taken up more by some parts versus other parts, contrast is shown + stains may be used simultaneously

how to use:

1) clipping slide onto stage
2) lowest-powered objective lens chosen
3) use of coarse adjustment knob to move objective lens down to just above the slide
4) look down eyepiece(ocular lens) and adjust focus via fine adjustment knob until clear image is achieved
5) for greater magnification, switch to higher-powered objective lens

Question 3

laser scanning confocal microscope

Answer 3

1) use laser beams to scan a specimen tagged with a fluorescent dye
2) laser causes dye to fluoresce which is focused through pinhole(out of focus light is blocked to increase clariy of image) onto detector which is hooked up to a computer, which generates an image(could be 3D)
3) useful for objects at different depths in thick specimens

Question 4

transmisson electron microscope(TEM)

Answer 4

1) use elecromagnets to focus a beam of electrons which is then transmitted through the specimen
2) denser parts of the specimen absorb more electrons which makes them appear darker on the image
3) High resolution is useful(range of organelles) but can only be used on thin specimens

staining

1) objects dipped in solution of heavy metal(lead)
2) metal ions scatter the electrons creating contrast and some parts of image appear darker than others

Question 5

scanning electron microscope(SEM)

Answer 5

1) scan a beam of electrons across the specimen
2) this knocks off electrons from the specimen, which is gathered in a cathode ray tube to form an image
3) images produced show the surface of the specimen and can be3D
4) lower resolution than TEMs

staining

1) objects dipped in solution of heavy metal(lead)
2) metal ions scatter the electrons creating contrast and some parts of image appear darker than others

Question 6

summary of microscopes

Answer 6

light = max res: 0.2um max mag: x1500
TEM = max res: 0.0002um max mag: x1 000 000
SEM = max res: 0.002um max mag: x500 000

Question 7

staining

Answer 7

in light and TEMs it passes through the object being viewed, as some parts of the object absorb more light than others
sometimes due to transparency the image appears white as rays/electrons pass directly through

Question 8

microscope slide preparation

Answer 8

slide= strip of clear glass/plastic which is flat/welled(for liquid)

dry mount -

1) thin slice
2) use tweezers to pick up and place in middle of clean slide
3) coverslip(square of thin/transparent plastic/glass) placed on top

wet mount -

1) pipette drop of water onto slide + tweezers specimen onto water drop
2) cover slip via tilt upright to reduce air bubbles
3) stain added added to edge + paper towel opposite edge to draw the stain

Question 9

organelles

Answer 9

RER - folds+processes proteins made at ribosomes
SER - synthesises+processes lipids
golgi apparatus - processes+packages new lipids proteins / produces lysosomes
centrioles - found in animal cells made of microtubules involved in chromosome separation during cell division
cilia - 9+2 formation of protein microtubules used to move substances along the cell surface
flagellum - 9+2 formation of protein microtubules used to propel cell forward

Question 10

protein production

Answer 10

1) protein made at ribosomes(RER=excreted/attached to cell membrane / free ribosomes=stay in cytoplasm)
2) in RER proteins are folded and processed
3) transported to Golgi apparatus in vesicles
4) at golgi appartus, further processing
5) proteins enter more vescles to be transported around the cell

Question 11

cytoskeleton

Answer 11

functions require energy from respiration so this can be inhibited by respiratory inhibitors
functions:
1) microtubules+microfilaments support cell’s organelles keeping them in position
2) help to strengthen the cell and maintain it’s shape
3) responsible for the movement of materials within the cell(movement of chromosomes during cell division)
4) cell movement(cilia + flagella powered by cytoskeletal protein filaments which run through them)

Question 12

different eukaryotes/prokaryotes

Answer 12

prokaryotes - eukaryotes

1. less than 2um - about 10-100um
2. DNA is circular - DNA is linear
3. No nucleus(DNA-free) - nucleus is present(DNA contained)
4. cell wall made of polysaccharide(peptidoglycan) - no cell wall(animals) cellulose(plant) chitin(fungi)
5. few organelles/no membrane-bound organelles - many organelles/membrane bound
6. flagella(flagellin arranged in helix) - flagella(microtubules ‘9+2’)
7. small ribosomes - larger ribosomes