1) Which of the following statements is consistent with the structure of the Kcs
ID: 181052 • Letter: 1
Question
1) Which of the following statements is consistent with the structure of the KcsA K+ channel?
a) This protein is a homotetramer composed of hydrophobic alpha helices that form a central channel that is hydrophilic.
b) This protein is a homotetramer composed of hydrophobic alpha helices that form a central channel that is hydrophilic at the openings and hydrophobic in the middle. c) This protein is a heterotetramer composed of hydrophobic alpha helices that form a central channel that is hydrophilic.
d) This protein is a heterotetramer composed of hydrophobic alpha helices that form a central channel that is hydrophilic at the openings and hydrophobic in the middle.
2) In this structure, the K+ ions are partly stabilized by several ______ that point toward and _____ the cations.
a)backbone carbonyl oxygens; donate electron density to
b) side chains; donate electron density to
c)backbone carbonyl oxygens; accept electron density from
d) side chains; accept electron density from
3)As described in Chapter 10, the amino acid residues that help to selectively transport K+ are known as the “signature sequence” and are common to K+ channels; what are these amino acids and where are they in the primary structure of Chain A in 1BL8?
a) VGYGD; residues 76–80
b) TVGYG; residues 75–79
c) TTVG; residues 74–77
d) TATTVG; residues 72–77
4) As implied in Chapter 10, what role does Asp 80 from each subunit play in the transport of K+?
a) These residues assist in attracting positive ions.
b) These residues coordinate K+ and stabilize the protein-bound state of K+.
c) These residues assist in removing the hydration shell surrounding the K+ ion.
d) Each of these factors is involved in the transport of K+.
5) As explained in Chapter 10 and indicated by the stoichiometry shown in 1BL8, what promotes the flow of K+ into the channel during the initial stages of the transport and what prevents the K+ from getting stuck in the carbonyl-rich region?
a) K+ ions are forced into the channel due to the hydrophobic nature of the central region of the channel.
b) As indicated by the structural analysis, the protein undergoes a conformational change that promotes the flow of K+.
c) The interactions between K+ ions and the backbone carbonyls are not stabilizing.
d) K+ ions are essentially forced into the channel by electrostatic repulsions resulting from the binding of additional K+ ions.
6) During the transport of K+, what prevents the K+ from remaining bound within the protein channel?
a) K+ ions are essentially forced out due to the hydrophobic nature of the central region of the channel.
b) As indicated by the structural analysis, the protein undergoes a conformational change that ultimately releases the K+.
c) The interactions between K+ ions and the backbone carbonyls are not stabilizing.
d) K+ ions are essentially forced out due to the entry of additional ions into the channel.
7) What promotes the exit of K+ from the channel?
a) K+ ions are essentially forced out due to the hydrophobic residues located at the exit of the channel.
b) As indicated by the structural analysis, the protein undergoes a conformational change that ultimately releases the K+.
c) The interactions between K+ ions and the polar residues at the channel’s exit and the lower concentration of K+ on the exiting side of the channel assist in the exit of K+.
d) K+ ions are essentially forced out due to the entry of additional ions into the channel.
8)As indicated by the PDB pages for 4CHW and 4CHV, the K+ channel MloK1 is a _____________ and is controlled by __________.
a)ligand-gated channel; cyclic AMP
b) signal-gated channel; Ca2+
c) ligand-gated channel; cyclic ATP
d) signal-gated channel; Na+
9) As shown by the structural alignment of Chain A from 4CHW and 4CHV, the subunits possess _____________ conformation/s.
a) the exact same
b) drastically different
c) slightly different
10) This information suggests that binding of ______ induces a conformational change that results in __________ and increased transport of K+.
a) cAMP; closing of the channel
b) AMP; closing of the channel
c) cAMP; opening of the channel
d) AMP; opening of the channel
Explanation / Answer
Ques-1:) Which of the following statements is consistent with the structure of the KcsA K+ channel?
Answer: b) This protein is a homotetramer composed of hydrophobic alpha helices that form a central channel that is hydrophilic at the openings and hydrophobic in the middle.
Reason:
KcsA K+ channel (53 angstroms) is bacterial protein channels as a an integral membrane protein & located on the cell membrane with four identical subunits therefore homotetramer, in which middle amino acid residues are mostly hydrophobic (34Ao) and outer & inner opening residues are mostly hydrophillic (outer extracellular space & intracellular space- hydrophillic residues)
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