Methods of Studying Cells - 3.1

Question 1

What are microscopes?

Answer 1

Instruments that produce a magnified image of an object.

Question 2

What is the equation of magnification?

Answer 2

Magnification = size of image/size of real object.

Question 3

What is the resolution of a microscope?

Answer 3

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

Question 4

What is the resolving power of a light microscope?

Answer 4

About 0.2um

Question 5

What is cell fractionation?

Answer 5

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

Question 6

Before fractionation, what must the tissue be placed in?

Answer 6

A cold, buffered solution of the same water potential as the tissue.

Question 7

What are the features of the solutions in which the tissue is placed?

Answer 7

• Cold - to reduce enzyme activity that might break down organelles.
• is of the same water potential as the tissue - to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water.
• Buffered - so that the pH does not fluctuate. Any change in pH could alter the structure of the organelles or affect the functioning of enzymes.

Question 8

What are the two stages of cell fractionation?

Answer 8

Homogenation and Ultracentrifugation

Question 9

What happens in homogenation?

Answer 9

Cells are broken up by a homogeniser (blender). This releases organelles from he cell. The resultant fluid, known as homogenate, is then filtered to remove any complete cells and large piece of debris.

Question 10

What is ultracentrifugation?

Answer 10

The process by which the fragments in the filtered homogenate are separated in a machine called a centrifuge. This spins tubes of homogenate at very high speed in order to create a centrifugal force.

Question 11

What is the process of ultracentrifugation?

Answer 11

• The 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 the sediment of nuclei.
• The supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before.
• The next heaviest organelles, the mitochondria, are forced to the bottom of the tube.
• the process is continued in this way so that, at each increase in speed, the next heaviest organelle is sedimented and separated out.