Many bacteria have cell surface extensions called fimbriae or pili that play a r

Question

Many bacteria have cell surface extensions called fimbriae or pili that play a role in either motion or gene transfer. These surface extensions arc composed of protein, namely the protein called pilin. Following is a picture of the pilin protein of Salmonella Typhi [RCSB Protein Databank). Notice that the region labeled A is exposed to the aqueous environment whereas the region labeled B is within the protein interior. Region C shows a tight turn in the protein. Thus, all of the following arc true. EXCEPT The amino acid Asp is more likely to be seen in region A than in region B. F, V, I and M are more likely found in region B than in region A. Proline is more likely in region A than in region C. Arg and Lys are more likely found in region A than in region B. The pilin protein contains both alpha-helical and beta-sheet secondary structures. Following are two molecules Which statement/s regarding these two molecules is TRUE? Molecule 1 is an amino acid Molecule 2 is highly hydrophobic. Molecule 2 is the building block of polysaccharides such as glycogen. Molecule 1 is a phospholipid. Molecule 2 is the building block of proteins.

Explanation / Answer

Question 2 is the easier one. Molecule 1 is a DNA nucleotide. You know this because on the bottom right carbon it has two hydrogen substituents and no hydroxyl (ie "DEoxyribonucleic" acid). Molecule 1 is glucose. So the answer should be C, since glycogen is composed of glucose monomers. Question 1 notes a few clues: Region A - hydrophilic amino acids here Region B - hydrophobic amino acids here Region C - aa with a 'twist' in their R-groups here To evaluate the answers: a. True - since "ASPartic acid" is an acid, thereby polar and hydrophilic in basic pH of blood b. True - phenylalanine (F), valine (V), isoleucine (I), and methionine (M) are all hydrophobic, organic R-groups with no polar areas c. False - proline is classically found in beta sheet turns/twists of a protein, so it is very likely to be in Region C d. True - Arginine and Lysine are basic, so same logic as answer a. e. True - in the structure, the spirals are alpha helices and the flat thick areas are beta sheets The best way to solve questions like #1 is process of elimination (a, b, d, e are 'more likely' answers)

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