Cell Structure Flashcards
What is magnification?
How many times bigger the image of the object is bigger than the actual size
What is resolution?
The minimum distance two objects can be apart in order for them to be seen as separate items
What is the equation used to find magnification?
Magnification = image size/actual size
What is the equation used to find actual size?
Actual size = image size/magnification
What is cell fractionation?
The process where cells are broken up and the different organelles they contain are separated
What conditions does the solution need to be before adding the tissue for cell fractionation?
- Cold
- Isotonic
- Buffered
Why does the solution need to be cold when putting in the tissue for cell fractionation?
To reduce enzyme activity that may break down the organelles
Why does the solution need to be isotonic when putting in the tissue for cell fractionation?
To prevent organelles bursting or shrinking as a result of osmotic gain or loss of water
Why does the solution need to be buffered when putting in the tissue for cell fractionation?
So that the pH doesn’t fluctuate which could alter the structure of the organelles or the function of the enzymes
What is used in cell fractionation to break up the cells?
A homogeniser (blender)
What is the fluid called after homigenisation has happened?
Homogenate
What happens after homogenisation?
The homogenate is filtered to remove any complete cells and large pieces of debris
What is ultracentrifugation?
Process of which the fragments of filtered homogenate is separated in a centrifuge
What is the process of ultracentrifugation for animal cells?
- The filtered homogenate is placed in the centrifuge and spun at a low speed
- This forces the heaviest organelles to the bottom of the tube, forming a ‘pellet’
- The supernatant is moved to another tube and span again at a faster speed
- The next heaviest organelles are forced to the bottom.
- This is repeated until the desired organelle is separated
Why do light microscopes have poor resolution?
The relatively long wavelength of light
What are the two types of microscope?
- Light microscope
- Electron microscope
What are 2 advantages of the electron microscope over the light microscope?
- The electron beam has a very short wavelength therefore it has a high resolving power
- As electrons are negatively charged the beam can be focused using electromagnets
What is the resolving power of a modern electron microscope?
0.1nm apart, 2000 times better than a light microscope
What are the two types of electron microscope?
- Transmission (TEM)
- Scanning (SEM)
How does a TEM work?
An electron gun produces a beam of electrons focused by a condenser electromagnet. The beam passes through a thin specimen, with parts absorbing electrons (appearing dark) and others allowing electrons to pass through (appearing bright). The image produced on a screen can be photographed to create a photomicrograph.
Why cant a TEM always achieve a 0.1nm resolving power?
- The preparation of the specimen is difficult so can limit the the resolution
- A higher energy electron beam is required and this may destroy the specimen
What are the limitations of the TEM?
- Specimen must be dead as the system has to be in a vacuum
- A complex staining method is required and image isn’t in colour
- Specimen must be extremely thin
- Artifacts may appear
What is a limitation of the TEM but not an SEM?
The specimen for an SEM doesn’t have to be thin as no electrons penetrate the specimen in an SEM
How does an SEM work?
The SEM directs a beam of electrons onto the specimen’s surface from above, scanning it in a regular pattern. The scattering of electrons, which varies with the specimen’s contours, helps build a 3D image with the aid of a computer.
What is the resolving power of an SEM?
About 20nm