Test on Cryo-Electron Microscopy for Structural Biology

Question 1: Fitting known crystal structures into an electron density map is a method used to interpret a 3D map generated through cryo-electron microscopy.

A. Ano

B. Ne

Explanation: To interpret a 3D map, one approach is to fit known crystal structures into the electron density map, as stated under the 'And then?' section of the study materials.

Question 2: Which staining method involves placing the sample on a dried film of heavy metal salt, leading to the object appearing as a light spot on a black background?

A. Positive Staining

B. Negative Staining

C. Shadowing

D. Cryo-Electron Microscopy

Explanation: According to the study materials, 'Negative Staining' involves placing the sample on a dried film of heavy metal salt, where the object appears as a light spot on a black background. Positive Staining and Shadowing have different descriptions, and Cryo-Electron Microscopy is an alternative to harsh staining methods, not a staining method itself.

Question 3: The semi-angle  talpha t is defined as the semi-angle below which the light is stopped by the aperture.

A. Ano

B. Ne

Explanation: The study materials state that " talpha t is the semi-angle above which the light is stopped by the aperture" (Figure 2.3 and accompanying text). Therefore, the statement that it is the semi-angle below which light is stopped is incorrect.

Question 4: Resolution represents the largest distance between two points on an object that can be clearly seen as separate through a microscope.

A. Ano

B. Ne

Explanation: The study materials define resolution as "the closest distance between two points on the object which can be clearly seen through the microscope to be separate entities," not the largest distance.

Question 5: According to the provided materials, which statement accurately describes the relationship between the Nyquist frequency ($f_N$) and the sampling frequency ($f_s$)?

A. The Nyquist frequency is twice the sampling frequency.

B. The Nyquist frequency is equal to the sampling frequency.

C. The Nyquist frequency is one-half the sampling frequency.

D. The Nyquist frequency is the maximum frequency that can be accurately represented with aliasing.

Explanation: The study materials state: 'For a given sampling frequency, the maximum frequency you can accurately represent without aliasing is the Nyquist frequency, which equals one-half the sampling frequency, as shown by the following equation. $f_N = f_s / 2$.' This directly supports the option that the Nyquist frequency is one-half the sampling frequency.