Flashcards in Electron Microscopy 3 Deck (14):

1

## How is the image produced related to the actual object?

### The image is a 2D projection of a 3D object.

2

## What does intensity represent in the 2D image?

### Depth.

3

## Why are multiple 2D images used?

### These projections show different orientations of the 3D object.

4

## To overcome the bad signal-to-noise ratio what must assume about the single particles and what must be done to them?

###
Must assume that they are all the same.

Then average the single particles and filter out the noise.

5

## What must be done to create the 3D model from the 2D images?

### Must use the relationship between 2D and 3D Fourier transforms to obtain a 3D model.

6

## What is a Fourier Transform?

### It is a convenient mathematical representation of images - (sine waves)

7

## What can you use a Fourier Transform to do?

### You can go back and forth between real space (image) and reciprocal/Fourier space (transform) by using the Fourier transform equation and its inverse equation.

8

## What is the method to generate the structure?

###
Collect all 2D images (orientations) - use the Fourier transform to relate all them together - then do the inverse Fourier transform of the all the related orientations to generate the structure.

(Note = think paper in box analogy).

9

## What does the projection theorem describe?

###
The relationship between 2D projections collected on the electron microscope and the 3D Fourier transform of the original object.

10

## What does the positioning of the central sections of the 3D Fourier transform depend on?

### The orientation parameters of the 2D projection.

11

## What are the Fourier transforms in EM?

### These are the different orientations of the molecule.

12

## Why will the averages of the single particles differ slightly from the original object?

### They do not completely align - they are all in slightly different orientations.

13

## What can averaging significantly different images do to the overall image?

### Degrade the quality and make very noisy.

14