2007mt - Biology 200 Section 102 Midterm Exam - Oct 16,...

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Biology 200 Section 102 Midterm Exam - Oct 16, 2007 Average = 62.5%; 15% of class =>80%, 23% of class <50% Distribution of marks XXX XXXX XXXXX XXXXX XXXX XXXXX XXXXX XXXXX 75 23 XXXXX XXXXX XXXXX XXXXX XXX 70 20 XXXXX XXXXX XXXXX XXXXX 65 32 XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XX 60 22 XXXXX XXXXX XXXXX XXXXX XX 55 28 XXXXX XXXXX XXXXX XXXXX XXXXX XXX 50 17 XXXXX XXXXX XXXXX XX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XX XXXXX XXXXX XXXXX XXXX XX X 1. (15 marks, 15 minutes) Self-assembly is an important principle at the molecular level. Discuss with examples how this applies to biological macromolecules and membranes. Take a couple of minutes to plan your answer before you start. A concise thesis statement may help you stay on track. Self-assembly is the post-synthetic process whereby macromolecules or membranes come to assume their minimum-energy three-dimensional structure through interaction of molecular groups with water, with other groups within the same molecule and with other molecules through a combination of hydrophilic and hydrophobic interactions. Student Essay #1 Self-assembly is an important cellular process at the level for macromolecules such as RNA and protein(#). Self-assembly also has consequences for larger structures such as the phospholipid bilayer membrane(#). Proteins can self-assemble after synthesis with the assistance of enzymes called chaparones (#). Proteins are made of four kinds of amino acids, basic, acidic, polar, uncharged and non-polar (#). These amino acids interact with the aqueous environment of a cell (#) and with each other to form the most energetically favourable combination of a protein almost spontaneously (#). Due to the chemical nature of the amino acids, they will favour different regions of
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the protein. For instance the non-polar amino acids will assemble the protein in such a way that they are shielded from the aqueous environment and are situated on the inside of a folded protein(#). Conversely, the polar amino acids will be on the outside of a newly self-assembled protein(#). Interactions between specific groups after the initial self-folding will strengthen the energetically favourable protein structure(#). These interactions include ionic bonds (#) and covalent bonds such as disulfide bridges. One protein can therefore self-assemble based on the sequence of amino acids. RNA molecules can self-assemble and self-process too(#). For instance tRNA molecules can create their characteristic L-shape by base pairing within itself(#). In addition, tRNAs have self-splicing introns and can create their final base sequence (#). Phospholipid bilayers are probably the most effective example of self-assembly on a larger scale(#). Due to the amphipathic nature of the phospholipids (#) (hydrophilic polar head group and hydrophobic hydrocarbon tails(#)).
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2007mt - Biology 200 Section 102 Midterm Exam - Oct 16,...

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