On average, how many amino acids engaged in predominantly hydrophobic ?-helices does it take to cross the hydrophobic part of the membrane?
A) about 10 amino acids
B) about 20 amino acids
C) at least 40 amino acids
D) about 2 - 3 amino acids
E) None of these are correct.

11. In a protein sequence, which repeated sequence over a twenty amino acid stretch would most likely lead to insertion of a transmembrane domain into a lipid bilayer.
A) Serine-Threonine-Alanine-Histidine
B) Glycine-Proline-Proline-Serine
C) Valine-Leucine-Iosleucine-Leucine
D) Arginine-Lysine-Proline-Arginine
E) Proline-Lysine-Proline-Alanine
Explain:
12. Which group of amino acids would most likely be found in an enzyme active site?
A) Serine-Threonine-Alanine-Histidine
B) Glycine-Proline-Alanine-Serine
C) Valine-Leucine-Iosleucine-Serine
D) Histidine -Lysine-Glutamic Acid -Arginine
E) Proline-Lysine-Glycine-Alanine
Explain:
22. During isoleucine synthesis, excess end product of the metabolic pathway shuts down the pathway.
How does this negative feedback benefit the cell?
A) Decreases the levels of threonine
B) Increases the amount of end product.
C) Prevents a cell from wasting chemical resources
D) Increases the activity of threonine deaminase
E) Increases the availability of glycine in the cell.