Cell Structure 3 Oct 2021
Cell Structure
Methods of studying cells
Magni cation is how much bigger the image is then the
object.
Resolution is how detailed the image is, and how far the
microscope can distinguish between two points.
Optical (light) Microscopes
Maximum Resolution of 2μm.
Simple convex lens that uses beams of light.
Electron Microscope
Short wavelengths and has a high resolving power.
As electrons are negatively charged the electron beam
can be focused using electromagnets
At best the maximum resolution is 0.1nm (2000x better
than light microscopes)
Uses an electron gun that produces beams of electrons
that are focused onto the object by condenser
electromagnets
Transmission electron microscope
The beam passes through the object
Parts of the object absorb electron and appear dark
Other parts allow electron to pass through so they
appear bright.
Limitations are:
- Whole system must be in vacuum thus all living
specimen cannot be observed.
- Complex staining process
- Specimen must be very thin
- Image can be unclear because of artefacts which are
remains from the staining process or dust air bubbles
etc
Scanning Electron Microscope Light Microscope
SEM specimens don’t have to be very thin as the
electrons don’t need to go through the specimen.
SEM directs beam on the surface.
However SEM has a lower resolving power then TEM
TEM SEM
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, Cell Structure 3 Oct 2021
Cell Fractionation
Cell Fractionation is the process where
cells are broken up and the di erent
organelles they contain are separated.
Before this process begins the tissue must
be placed in a cold, bu ered solution of
the same water potential as the tissue
Cold -to reduce enzyme activity that might
break down organelles
Same water potential - to prevent
organelles bursting or shrinking because
of di erence
Bu ered - so that the pH does not change
Two Stages of cell fractionation:
Homogenation - breaking up the cells
- Cells are broken up by either being vibrated or grinder in a blender
- This breaks up the plasma membrane and releases all the organelles into the solution
- Then it is ltered to get the large pieces out
Ultracentrifugation - separating the organelles
- The cell fragments are poured into a tube, which is put into a centrifuge
- The heaviest organelles like nuclei get ung to the bottom into a thick substance called a
sediment
- The rest of the organelles stay suspended in the uid above this is called the supernatant.
- The supernatant is drained o and poured into another tube which is put into a centrifuge, the
heavier organelles go to the sediment etc
- This process is repeated at high and higher speeds until all the organelles are separated out
- This is the order: nuclei, (chloroplasts), mitochondria, lysosomes, endoplasmic reticule then
ribosomes
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Cell Structure
Methods of studying cells
Magni cation is how much bigger the image is then the
object.
Resolution is how detailed the image is, and how far the
microscope can distinguish between two points.
Optical (light) Microscopes
Maximum Resolution of 2μm.
Simple convex lens that uses beams of light.
Electron Microscope
Short wavelengths and has a high resolving power.
As electrons are negatively charged the electron beam
can be focused using electromagnets
At best the maximum resolution is 0.1nm (2000x better
than light microscopes)
Uses an electron gun that produces beams of electrons
that are focused onto the object by condenser
electromagnets
Transmission electron microscope
The beam passes through the object
Parts of the object absorb electron and appear dark
Other parts allow electron to pass through so they
appear bright.
Limitations are:
- Whole system must be in vacuum thus all living
specimen cannot be observed.
- Complex staining process
- Specimen must be very thin
- Image can be unclear because of artefacts which are
remains from the staining process or dust air bubbles
etc
Scanning Electron Microscope Light Microscope
SEM specimens don’t have to be very thin as the
electrons don’t need to go through the specimen.
SEM directs beam on the surface.
However SEM has a lower resolving power then TEM
TEM SEM
1 of 10
fi
, Cell Structure 3 Oct 2021
Cell Fractionation
Cell Fractionation is the process where
cells are broken up and the di erent
organelles they contain are separated.
Before this process begins the tissue must
be placed in a cold, bu ered solution of
the same water potential as the tissue
Cold -to reduce enzyme activity that might
break down organelles
Same water potential - to prevent
organelles bursting or shrinking because
of di erence
Bu ered - so that the pH does not change
Two Stages of cell fractionation:
Homogenation - breaking up the cells
- Cells are broken up by either being vibrated or grinder in a blender
- This breaks up the plasma membrane and releases all the organelles into the solution
- Then it is ltered to get the large pieces out
Ultracentrifugation - separating the organelles
- The cell fragments are poured into a tube, which is put into a centrifuge
- The heaviest organelles like nuclei get ung to the bottom into a thick substance called a
sediment
- The rest of the organelles stay suspended in the uid above this is called the supernatant.
- The supernatant is drained o and poured into another tube which is put into a centrifuge, the
heavier organelles go to the sediment etc
- This process is repeated at high and higher speeds until all the organelles are separated out
- This is the order: nuclei, (chloroplasts), mitochondria, lysosomes, endoplasmic reticule then
ribosomes
2 of 10
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fi ff ffff fl fl
