16 Questions
Why are proline kinks important in membrane proteins?
To allow side chains to be placed more freely
What is the purpose of partially unwound helices in transmembrane proteins?
To allow side chains to be positioned more freely
Why do helices prefer to pack at an angle to one another?
Because they can only interact well for a limited number of turns
What happens when helices are packed in a parallel orientation?
They cannot pack well due to diagonal orientation of side chain ridges
How can 2 short helices mimic one long helix in multi-spanning TM proteins?
By turning back after partially crossing the bilayer
What is the consequence of helices diverging too far to interact well?
It results in poor interaction between neighboring helices
Which of the following statements about helix packing is true?
All of the above statements about helix packing are true.
What is the significance of the GXXXG motif in alpha helices?
The GXXXG motif brings two glycine residues to the same face of the helix, creating a groove for another helix to approach closely.
Which of the following statements about monotopic membrane proteins is correct?
Monotopic membrane proteins have small hydrophobic domains that interact with only one leaflet of the membrane bilayer.
What is the significance of conserved glycine residues in transmembrane helix-helix interactions?
Conserved glycine residues provide flexibility and allow closer helix-helix interactions.
Which of the following statements about pi (π) helices is correct?
Pi helices involve hydrogen bonding between the C=O of residue i and the NH of residue i+5.
What is the primary reason why proline residues are not commonly found in the interior of protein secondary structures?
Proline's amide nitrogen lacks a hydrogen atom, preventing it from participating in hydrogen bonding.
What effect does the presence of a proline residue have on the structure of an α-helix?
It introduces a kink or distortion in the helix due to the inability of proline to participate in hydrogen bonding.
Which of the following statements about the peptide bond configuration is correct?
The cis configuration of the peptide bond is often found in β-turns, while the trans configuration is more common in α-helices and β-sheets.
Which of the following statements about helix packing in proteins is correct?
Helix packing is primarily driven by hydrophobic interactions between the side chains of non-polar residues.
Which of the following statements about partially unwound helices is correct?
Partially unwound helices are characterized by a change in the hydrogen bonding pattern, leading to a local disruption in the helical structure.
This quiz covers the concept of helical packing in membrane proteins, focusing on how the ridges of one helix pack against the grooves of another. It discusses the 4-4 packing where helices cross at an angle of 50°, the 3-4 packing where helices cross at an angle of 20°, and the knobs-into-holes packing of side chains.
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