cell structure Flashcards
how far apart do two objects need to be for a light microscope to distinguish between them?
0.2um or further
when do convex glass lenses work more effectively?
if used in pairs in a light microscope
which has shorter wavelength/beams electrons or light?
electrons
how far apart do two objects need to be for a electron microscope to distinguish between them?
1nm
whats the magnification equation?
magnification + size of image/ size of real object
whats 1mm in nm?
1,000,000nm
whats the resolution or resolving power of a microscope?
the minimum distance apart two objects can be in order for them to appear as separate items
does increasing magnification and therefore increasing the size of the image increase resolution?
not always
whats cell fractionation?
processes where cells are broken up and the different organelles they contain are separated out
why is the solution used in cell fragmentation cold?
to reduce enzyme activity that might breakdown organelles.
why is the solution used in cell fragmentation the same water potential as the tissue?
to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water
why is the solution used in cell fragmentation buffered?
so that pH does not fluctuate. Any change in pH could alter the structure of the organelles or affect the functioning of enzymes
whats homogenation?
the first step in cell fragmentation when cells are broken up by a homogeniser (blender) releasing organelles from the cell. The resultant homogenate, is then filtered to remove any complete cells and large pieces of debris?
whats ultracentrifugation?
the second step in cell fragmentation when the fragments filtered by the homogenate are separated in a centrifuge
what does a cetrifuge do?
spins tubes of homogenate at a very high speed to create a centrifugal force
whats the centrifugal process for animal cells?
-tube of filtrate is placed in the centrifuge and spun at a slow speed
- the heaviest organelles, the nuclei, are forced to the bottom of the tube, where they form a thin sediment or pellet
- the fluid at the top of the tube (supernatant) is removed leaving just the sediment
- the supernatant is then transferred into another tube and spun in the centrifuge faster the before
-the the next heaviest organelles, the mitochondria are forced to the bottom of the tube
-process is repeated at increasing speed for the rest of the organelles
what speed of centrifugation is needed for nuclei to be separated out?
1000 revolutions min -1
what speed of centrifugation is needed for mitochondria to be separated out?
3500 revolutions min-1
what speed of centrifugation is needed for lysosomes to be separated out?
16500 revolutions min -1
whats the advantages of an electron microscope?
- high resolving power due to short wavelength on electron beam
- electrons are negatively charged so beam can be focused using electromagnets
in electron microscopes how do the stop electrons being absorbed or deflected by molecules in the air?
a near-vacuum is created
how does a TEM work?
an electron beam passes through a thin section of the specimen. parts of the specimen absorbs electrons and appear dark other parts allow electrons to pass through so appear bright the image is produced of a screen and can be photographed to give a photomicrograph.
why cant a TEM always reach its resolving power of 0.1nm?
- difficulties preparing the specimen limit the resolution that can be achieved
- a higher electron beam that is required may destroy the specimen
what are the main limitations of the TEM and SEM?
-living specimens cannot be observed due to the vacuum
- complex staining process
-image may contain artefacts
can the TEM produce 3D images?
no an extremely thin specimen is required so the image produced is 2D to create a 3D image with a series of photomicrographs however this is slow and complicated
how does the SEM work?
the electron beam is passed back and forth across a portion of the specimen in a regular pattern. The electrons are scattered by the specimen which depends on the contours of the specimen surface allowing a 3D image to be built
whats the resolving power of the basic SEM?
20nm
