cell structure Flashcards
place there units in order from smallest to largest:
kilometre, metre, micrometre, millimetre, nanometre
- nanometre
- micrometre
- millimetre
- metre
- kilometre
match the unit up to their equivalence to metres:
kilometre, metre, millimetre, micrometre, nanometre
km = 1000m
m = 1m
mm = 10^-3
um = 10^-6
nm = 10^-9
what is the minimum distance between 2 points that a light microscope can resolve?
200nm or 0.2 umw
what is the maximum useful magnification of a light microscope?
1500
what is the definition of magnification?
how much bigger the image is than the real specimen
what is the definition of resolution?
the ability to distinguish between two points that are close together, and see them as separate structures
what is the equation for magnification?
magnification = image size/actual size
what is cell fractionation and ultracentrifugation?
a method used to break open cell and separate all of the organelles
before the cells are broken open, they need to be placed in a solution. what 3 things does this solution need to be?
- cold
- isotonic
- buffered
why does the solution that cells are placed in before they are broken open and centrifuged need to be cold?
because this reduces enzyme activity that could lead to the break down of organelles
why does the solution that cells are placed in before they are broken open and centrifuged need to be isotonic?
so that the solution has the same water potential as the cells and does not cause the cells to burst or shrink
why does the solution that cells are placed in before they are broken open and centrifuged need to be buffered?
so that the PH of the solution doesnt fluctuate and change the function of the enzymes or structure of organelles inside the cell
what are the two stages of cell fractionation?
- homogenisation
- ultracentrifugation
how is homogenisation of cells achieved and what is removed in the process?
- cells are broken up in a blender, which releases organelles from the cell
- the homogenate (resultant fluid) is then filtered to remove complete cells and debris
describe the process of ultracentrifugation
- cellular fragments are placed in a machine called a centrifuge
- fragments are spun at a low speed so the heaviest organelles are forced to the bottom, where they form a thin layer of sediment called pellets
- the supernatant (fluid at the top of the tube) is removed
- supernatant placed into another tube and spun again at a faster speed than before, forcing the next heaviest organelle to the bottom
- the process is repeated at faster speeds until all organelles are separated
at what speed of the centrifuge are the following organelles separated?;
nuclei, mitochondria, lysosomes
- nuclei = 1000
- mitochondria = 3500
- lysosomes = 16,500
what are the two types of electron microscope?
- transmission electron microscope (TEM)
- scanning electron microscope (SEM)
what is the highest magnification of a TEM?
500,000
how does a TEM work?
- electrons fired from an electron gun and pass through a section of the specimen
- electrons can behave as very short electromagnetic waves, so give a very high resolution
- the electron beam is focused using electromagnets
- the denser part of the specimen absorbs more electrons, so appears darker
- the image is then produced on a fluorescent or photographic plate
what is the resolution of a TEM?
0.1nm or 0.0001um
give 3 limitations of a TEM?
- living specimens cannot be viewed as specimens must be in a vacuum
- specimens must be extremely thin
- specimens must be killed and chemically fixed which is a complex and time consuming process
- this method can result in artefacts
- can only capture 2d images
- the image is in black and white
what is an artefact?
something that can appear on the final image created by a transmission electron microscope that is not a part of the specimen
how does a SEM work?
- electrons are passed across the surface of the specimen
- the scattered electrons form a image on a screen
- depressions in the specimen appear dark, and extensions appear light
- creates a 3d image
give 2 limitations of a SEM
- resolving power is less than a TEM (0.2nm)
- cant see inside cells
