This set of Protein Engineering Interview Questions and Answers for Experienced people focuses on “Ubiquitin-Proteasome Pathway of Protein Degradation”.
1. The proteolytic machinery acts after the chaperones have finished their tasks.
a) True
b) False
View Answer
Explanation: The proteolytic machinery and the chaperones compete with one other to recognize a modified protein. Hence, the above statement is false. The proteasome is a compartmentalized protease with sequestered active sites.
2. ATP dependent proteases constitute how much percent of the total cell proteins?
a) 0.2 percent
b) 10 percent
c) 0.1 percent
d) 1 percent
View Answer
Explanation: ATP dependent proteases constitute 1 percent of the total cell proteins. It cleaves target protein molecules into amino acids with the help of ATP.
3. Which of the following enzymes is the starting point of the Ubiquitin-conjugating system?
a) Ubiquitin ligase (E2-E3 complex)
b) Accessory proteins (E3)
c) Ubiquitin-conjugating enzyme (E2)
d) Ubiquitin-activating enzyme (E1)
View Answer
Explanation: Ubiquitin is prepared for conjugation to the other proteins by the ATP-dependent Ubiquitin-activating enzyme (E1). This creates an activated E1 bound ubiquitin that is subsequently transferred to one of a set of ubiquitin-conjugating (E2) enzymes. Thus, Ubiquitin-activating enzyme (E1) is the starting point.
4. Which of the following complex is known as Ubiquitin ligase?
a) E1-E3 complex
b) E2-E4 complex
c) E1-E4 complex
d) E2-E3 complex
View Answer
Explanation: The E2 enzymes act in conjugation with accessory proteins (E3). E2-E3 complex is known as a Ubiquitin ligase. It forms a polyubiquitin chain linked to the substrate protein.
5. Polyubiquitin chain is linked to which amino acid of the substrate protein?
a) Glycine
b) Proline
c) Methionine
d) Lysine
View Answer
Explanation: E2-E3 complex, called ubiquitin ligase binds to specific degradation signals called degrons in the protein substrates. This binding helps in linking the polyubiquitin chain to the lysine of the substrate proteins.
6. Which of the following recognizes the degradation signals on the abnormal proteins?
a) E4 molecules
b) E1 molecules
c) E2 molecules
d) E3 molecules
View Answer
Explanation: Denatured, misfolded, or abnormal proteins tend to present on their surface amino acid sequences that are recognized as degradation signals. It is the role of E3 molecules to recognize these signals.
7. Each end of the cylinder of the proteasome is normally associated with a large protein complex, the 19S cap.
a) False
b) True
View Answer
Explanation: The above statement is true. Each end of the cylinder of the proteasome is normally associated with a large protein complex, the 19S cap. This cap protein contains a six subunit protein ring through which target proteins are threaded into proteasome core.
8. Each proteasome consists of a central hollow cylinder, known as the 20S core proteasome.
a) False
b) True
View Answer
Explanation: The above statement is true. Each proteasome consists of a central hollow cylinder, known as the 20S core proteasome. It is formed from multiple protein subunits that assemble as a quasi-cylindrical stack of four heptameric rings.
9. The threading reaction which unfolds the target proteins as they move through the cap is not driven by ATP hydrolysis.
a) True
b) False
View Answer
Explanation: The above statement is false. The threading reaction which unfolds the target proteins as they move through the cap is driven by ATP hydrolysis. It unfolds the target proteins as they move through the cap.
10. Which of the following proteins is also known as unfoldases?
a) ACC proteins
b) ABC proteins
c) AAU proteins
d) AAA proteins
View Answer
Explanation: AAA proteins are also known as unfoldases. The protein that makes up the ring structure in the proteasome cap belongs to a large class of proteins called unfoldases.
11. Which of the following proteins does not move quickly through the pore of proteasome?
a) Abnormal proteins
b) Misfolded proteins
c) Unfolded proteins
d) Very stable proteins
View Answer
Explanation: Very stable proteins do not move quickly through the pore of the proteasome. Very stable protein substrates may require hundreds of cycles of ATP hydrolysis and dissociation before they are successfully pulled into the AAA rings. Whereas, abnormal proteins, misfolded proteins, and unfolded proteins move quickly through the pore of the proteasome.
12. Which property of lysine makes it a good candidate for linking of polyubiquitin chain?
a) Its hydrophobicity
b) Its electronegativity
c) Carboxyl group in the side chain
d) Amino group in the side chain
View Answer
Explanation: Lysine has an amino group as its side chain. This property of lysine makes it a good candidate for the linking of the polyubiquitin chain. Thus the ubiquitin chain is linked to a lysine on the substrate proteins through the amino group in its side chain.
13. The first ubiquitin molecule is linked to the lysine of substrate proteins by which of the following enzymes?
a) E1
b) E1-Ubiquitin complex
c) E2
d) E2-E3 complex
View Answer
Explanation: The first ubiquitin molecule is linked to the lysine of substrate proteins by the E2-E3 complex. It is also known as the Ubiquitin ligase enzyme. In this complex, the E3 component recognizes the substrate proteins and the E2 component links the first ubiquitin molecule.
14. The second and further ubiquitin molecules are added by which of the following enzymes to make the polyubiquitin chain?
a) E3
b) E2
c) E2-E3 complex
d) E1- ubiquitin complex
View Answer
Explanation: The second and further ubiquitin molecules are added by E1- ubiquitin complex to make the polyubiquitin chain. Whereas, the first ubiquitin molecule is added by the E2-E3 complex.
15. In the ubiquitin ligase enzyme complex, the ubiquitin molecule is attached to which of its component?
a) E4
b) E1
c) E3
d) E2
View Answer
Explanation: In the ubiquitin ligase enzyme complex, the ubiquitin molecule is attached to its E2 component. Hence, E2 is the component that attaches the ubiquitin molecule to the lysine of the substrate proteins.
Sanfoundry Global Education & Learning Series – Protein Engineering.
To practice all areas of Protein Engineering for Interviews, here is complete set of 1000+ Multiple Choice Questions and Answers.
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