CryoEM and X-Crystallography

What is X-ray crystallography primarily used for?

Determination of macromolecular structures.

What percentage of available atomic resolution structures are solved by X-ray crystallography?

About 90%.

What type of radiation do X-rays represent?

High energy electromagnetic radiation.

What is the typical wavelength of X-rays used in protein crystallography?

Approximately 1 Å (10^-10 m).

What is a major challenge when using X-ray crystallography on flexible proteins?

The structural arrangement may depend on crystal packing rather than reflecting the solution state.

What is the phase problem in X-ray crystallography?

The phase of the wave is lost in the diffraction pattern, which is necessary for structure determination.

How is the phase problem resolved in X-ray crystallography?

Using different methods not specified in the notes.

What technique is used to convert diffraction patterns into electron density maps?

Fourier transform.

What does the intensity of diffracted radiation from a single macromolecule indicate?

It is weak, and inelastic scatter can damage the molecule before data collection.

Why are protein crystals used in X-ray crystallography?

They minimize radiation damage and reinforce signals, creating a clearer diffraction pattern.

What is the first step in growing crystals for X-ray diffraction experiments?

Controlled precipitation of a protein in crystal form.

What is the purpose of using a goniometer during X-ray diffraction?

To slowly rotate the crystal and collect diffraction patterns at multiple angles.

What is the role of electron density maps in structural biology?

They help model the protein chain into the density map for structure refinement.

What is the significance of R-free in structure reliability?

It indicates how well the model fits a set of data not used in the iterative refinement process.

What is the main advantage of X-ray crystallography in structural biology?

It provides structural information at atomic resolution for macromolecules of various sizes.

What are the two types of interference that can occur with X-ray waves?

Constructive and destructive interference.

What happens to X-rays when they interact with the electronic clouds of atoms?

They are scattered in different directions.

What is required for solving the structure of a molecule using X-ray crystallography?

Crystallization of the molecule.

What is the role of salt and additives in crystal growth?

They aid in the crystallization process.

What is the effect of crystal symmetry on X-ray diffraction?

It allows for the signals that are in phase to become stronger.

What is the purpose of recording a pattern of diffracted X-rays?

To obtain structural information about the macromolecule.

What does the term 'coherent beam' refer to in X-ray crystallography?

A beam of X-rays that maintains a consistent phase relationship.

What is the main limitation of using X-ray crystallography for certain proteins?

It is difficult for flexible proteins, membrane proteins, and labile complexes.

What is the significance of the scattering angle in X-ray crystallography?

It provides information about the structure of the macromolecule.

What is the main goal of iterative refinement in X-ray crystallography?

To improve the accuracy of the atomic model based on the electron density map.

How does X-ray crystallography contribute to human health?

By providing structural information that can aid in drug design and understanding diseases.

What is the purpose of using R-free in data fitting?

To avoid overfitting the data.

What does a higher resolution in imaging increase?

The accuracy and detail of observations.

What can be observed at atomic resolution?

Side chains, bound waters, drug design, and rotamers in nucleic acids and proteins.

What is the interaction between X-rays and macromolecules used for?

To encode information on the position of atoms in the molecule.

What law is used to amplify the diffracted X-ray signal?

Bragg's law.

What type of microscopy uses electrons to create images?

Electron Microscopy (EM).

What are the two main types of Electron Microscopy?

Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM).

What is the main advantage of using cryoEM?

It does not require crystallization of the molecule.

What is the difference between negative stain EM and cryoEM?

Negative stain EM is simple and quick, while cryoEM is complex and provides higher resolution.

What does the phase change in transmitted electrons allow in TEM?

To record a 2D image of a 3D object.

What is the role of averaging in single particles cryoEM?

It improves signal to noise ratio.

What is the significance of the resolution revolution in cryoEM?

It represents continuous technological improvements in imaging methods.

What is required for high-resolution structure determination in cryoEM?

Significant expertise and time-consuming image analysis.

What happens to electrons when they pass through a sample in EM?

They can be scattered elastically or inelastically.

What is a key challenge in using cryoEM for systems under 100kDa?

The signal-to-noise ratio is low for high-resolution structure determination.

What does TEM stand for?

Transmission Electron Microscopy.

What is the purpose of using a detector behind the sample in TEM?

To record a 2D projection of a 3D object.

What type of sample preparation is used in negative stain EM?

Dried heavy atom dye.

What does cryoEM allow researchers to capture?

Different conformations and intermediates of macromolecular assemblies.

What is the main limitation of cryoEM compared to X-ray crystallography?

It is more demanding in terms of expertise.

What is the typical resolution achievable with single particles cryoEM?

Near-atomic resolution.

What is a common application of X-ray crystallography?

To obtain 3D structures of molecules.

What does the term 'vitrified water' refer to in cryoEM?

Water that has been frozen to preserve biological samples without ice crystal formation.

What is the main focus of the next lecture mentioned?

NMR spectroscopy.