Cell Structure Flashcards

1
Q

What is magnification?

A

How many times bigger the image of the object is bigger than the actual size

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2
Q

What is resolution?

A

The minimum distance two objects can be apart in order for them to be seen as separate items

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3
Q

What is the equation used to find magnification?

A

Magnification = image size/actual size

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4
Q

What is the equation used to find actual size?

A

Actual size = image size/magnification

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5
Q

What is cell fractionation?

A

The process where cells are broken up and the different organelles they contain are separated

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6
Q

What conditions does the solution need to be before adding the tissue for cell fractionation?

A
  • Cold
  • Isotonic
  • Buffered
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7
Q

Why does the solution need to be cold when putting in the tissue for cell fractionation?

A

To reduce enzyme activity that may break down the organelles

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8
Q

Why does the solution need to be isotonic when putting in the tissue for cell fractionation?

A

To prevent organelles bursting or shrinking as a result of osmotic gain or loss of water

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9
Q

Why does the solution need to be buffered when putting in the tissue for cell fractionation?

A

So that the pH doesn’t fluctuate which could alter the structure of the organelles or the function of the enzymes

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10
Q

What is used in cell fractionation to break up the cells?

A

A homogeniser (blender)

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11
Q

What is the fluid called after homigenisation has happened?

A

Homogenate

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12
Q

What happens after homogenisation?

A

The homogenate is filtered to remove any complete cells and large pieces of debris

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13
Q

What is ultracentrifugation?

A

Process of which the fragments of filtered homogenate is separated in a centrifuge

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14
Q

What is the process of ultracentrifugation for animal cells?

A
  • 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
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15
Q

Why do light microscopes have poor resolution?

A

The relatively long wavelength of light

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16
Q

What are the two types of microscope?

A
  • Light microscope
  • Electron microscope
17
Q

What are 2 advantages of the electron microscope over the light microscope?

A
  • 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
18
Q

What is the resolving power of a modern electron microscope?

A

0.1nm apart, 2000 times better than a light microscope

19
Q

What are the two types of electron microscope?

A
  • Transmission (TEM)
  • Scanning (SEM)
20
Q

How does a TEM work?

A

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.

21
Q

Why cant a TEM always achieve a 0.1nm resolving power?

A
  • 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
22
Q

What are the limitations of the TEM?

A
  • 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
23
Q

What is a limitation of the TEM but not an SEM?

A

The specimen for an SEM doesn’t have to be thin as no electrons penetrate the specimen in an SEM

24
Q

How does an SEM work?

A

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.

25
Q

What is the resolving power of an SEM?

A

About 20nm