Problem 12
Differentiate between ligand-gated and voltage-gated channels.
Problem 13
Is the following statement true or false? Explain. The sodium-glucose linked transporter does not depend on the hydrolysis of ATP.
Problem 14
List two forms of energy that can power active transport.
Problem 15
A stretch of 20 amino acids is sufficient to form an \(\alpha\) helix long enough to span the lipid bilayer of a membrane. How could this piece of information be used to search for membrane proteins in a data bank of primary sequences of proteins?
Problem 16
Lipid bilayers are self-sealing. If a hole is introduced, the hole is filled in immediately. What is the energetic basis of this self-sealing?
Problem 17
Differentiate between peripheral proteins and integral proteins.
Problem 20
The \(\mathrm{K}^{+}\) channel and the \(\mathrm{Na}^{+}\) channel have similar structures and are arranged in the same orientation in the cell membrane. Yet the Na^{+ chan- } nel allows sodium ions to flow into the cell and the \(\mathrm{K}^{+}\) channel allows potassium ions to flow out of the cell. Explain.
Problem 21
Explain why an \(\alpha\) helix is especially suitable for a transmembrane- protein segment.
Problem 22
The neurotransmitter acetylcholine, which activates a ligand-gated ion channel, is rapidly destroyed by the enzyme acetylcholinesterase. This enzyme, which has a turnover number of 25,000 per second,has attained catalytic perfection with a \(k_{\text {cat }} / K_{\mathrm{M}}\) of \(2 \times 10^{8}\) \(\mathrm{M}^{-1} \mathrm{s}^{-1} .\) Why is the efficiency of this enzyme physiologically crucial?
Problem 23
Both aspirin and ibuprofen inhibit prostaglandin \(\mathrm{H}_{2}\) synthase-1 and relieve inflammation. Aspirin functions by blocking a channel in the enzyme, thereby preventing access to the substrate. Ibuprofen does not block this channel but still inhibits the synthase. How might ibuprofen function?
