Wei Feng

Question 1

AFM

Answer 1

Tapping or contact mode
Label free imaging
Size distribution, topology, length, force measurements
Negative mica adheres to positive holders
Sample added and washed with Milli Q before drying
Laser measures probe deflection and plots against distance

Question 2

Force distance curves

Answer 2

Probe can stick to protein
Force to pull protein from surface can be calculated
Force will increase until the protein pulls away and force returns to zero
Intramolecular adhesive force and ligand binding

Question 3

Tip sample convolution artefact

Answer 3

Small probe is more accurate
Larger probes can be deflected before reaching protrusion
Gives false positive

Question 4

Electron microscopy

Answer 4

Formvar coating attached to carbon grids
Carbon layer stabilises film and stops heat
Vacuum pump to remove excess sample
Uranyl acetate to improve contrast
Electron gun has a cathode which emits electron
These are accelerated and where they pass through the sample this is dark

Question 5

Cryo TEM

Answer 5

-160 degrees
Below this there are no ice crystals
Chemical bonds broken by high energy electron beams
Low contrast
Metal can be added but this limits the res to 30A
High res is flash frozen but still has a low SN

Question 6

Structural modelling approaches

Answer 6

Electron tomography- single molecule at different angles
Single particle analysis- particles deposit in all directions. 3D structure obtained from averaging many particles per class

Question 7

Small angle scatting techniques

Answer 7

Doesn't need crystals or prep
Not limited by mass
Rapid method
100-1 nm only
Needs large conc