Cell Structure , Microscopes , Ultra Centrifugation Flashcards
What is the process of binary fission in prokaryotes
DNA and plasmids replicate
Cell elongates and DNA moves to opposite poles of the cell
Cytoplasm begins to divide and a new cell wall begins to form
Cytoplasm divides to produce 2 daughter cells each contain a DNA loop but contain a different number of plasmid copies
What is the magnification calculation
Magnification = size of the imagine / size of the object
What is resolution
The minimum distance apart that 2 objects can be in order for them to appear as 2 separate items
What is cell fractionation
Process where cells are broken up and the different organelles they contain are separated out
What has to happen before cell fractionation can begin
Tissue placed in a cold , buffered , isotonic solution
Why is the solution cold
To reduce enzyme activity that might break down the organelles
Why is it buffered
So that the pH does not fluctuate so no changes can alter the structure or the organelles or affect the functioning of enzymes
Why is it placed in isotonic solution
To prevent organelles bursting/ shrinking due to osmotic gain or loss of water
What happened in homogenisation
Blending breaks up the tissue to break open cell membranes and release the organelles
What is ultracentrifugation
Process where the fragments in the filtered homogenate are separated in a centrifuge
Spinning at high speeds creating a centrifugal force
What is the process of ultracentrifugation
Homogenising
Homogenate is filtered to remove large debris as these will sink to the bottom of the tube
Centrifuging- at slower speeds the larger fragments collect at the bottom of the tube forming a pellet and smaller ones remain near the top stay suspended in liquid called supernatant
Each time the supernatant is re spun at a higher speed and some of the smaller organelles collect at the bottom forming a new pellet
Method is repeated to collect smaller organelles
What organelle is the first pellet
Nuclei
What is a TEM
Electron gun that produces a beam of electrons focused on the specimen
Passes through a thin sample of specimen
Flat 2D image produced
Why cant the 0.1nm resolving power of teh tEM always be put into practice
Difficulties preparing the specimen
A higher energy electron beam is required which may destroy the specimen
Main limitations of the TEM
Can’t observe living organisms as they must be in a vacuum
Image is not in colour
Extremely thin specimen
May contain artefacts
What is an SEM
Directs a beam of electrons onto the surface of the specimen from above rather than below
Building up a 3D image
How’s SEM better than TEM
3D image , not a thin specimen
5 limitations of TEM
Very thin sample
No colour
Artefacts present
Long preparation time
Can’t see a lining organism
Describe how a sample or chloroplasts could be isolated form leaves
Homogenise the leaves
Filter the mixture
Ensure mixture is in an isotonic solution
Place mixture into a centrifuge and first spin at a slower speed to get rid of denser organelles
Then respond at a quicker pace to produce a pellet of the denser organelles
