1. 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
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.
2. 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)
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.
3. 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
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.
4. Polyubiquitin chain is linked to which amino acid of the substrate protein?
a) Glycine
b) Proline
c) Methionine
d) Lysine
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.
5. Which of the following recognizes the degradation signals on the abnormal proteins?
a) E4 molecules
b) E1 molecules
c) E2 molecules
d) E3 molecules
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.
6. Which of the following proteins is also known as unfoldases?
a) ACC proteins
b) ABC proteins
c) AAU proteins
d) AAA proteins
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.
7. 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
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.
8. 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
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.
9. 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
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.
10. In the ubiquitin ligase enzyme complex, the ubiquitin molecule is attached to which of its component?
a) E4
b) E1
c) E3
d) E2
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.