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Unformatted text preview: in (1)-(4)
The choice I am explaining is
(1) Fibrous proteins are roughly shaped like cylinders and globular proteins are roughly
shaped like spheres. Cylinders and spheres have different surface area to volume
ratios. Cylinders have higher surface area to volume ratios than spheres.
(2) Completely denaturing a protein means separating it into its constituent subunits
(polypeptide chains) and unfolding each polypeptide chain. The complete denaturation of
an oligomeric protein would yield > 1 polypeptide chain while the complete
denaturation of a
monomeric protein would yield only one polypeptide chain.
(3) Intrachain -S-S- bonds are simply those between two Cys residues present in the
same polypeptide. Such bonds can be present regardless of whether a polypeptide
occurs singly as a monomeric protein or as a subunit of an oligomeric protein.
(4) A single domain lipid soluble protein would be an integral membrane protein with no
globular domains. Its amino acid composition would be dominated by residues with
hydrophobic side chains. A single domain globular protein would have a hydrophilic
surface and hydrophobic core so its amino acid composition would include some residues
with hydrophobic side chains and some residues with hydrophilic side chains. Question #7 (4 points)
In the organic solvent dioxane, an amino acid chain composed entirely of leucine adopts an α-helical
conformation however one composed entirely of isoleucine adopts a “random coil conformation.” Explain the
reason for this. Note: The term “random coil” is used by protein biochemists to refer to a conformation lacking
any recognizable repetitive structure.
O = Dioxane
O Leucine and isoleucine side chains are chemically identical except they have
different branching patterns. Ile branches closer to the α -carbon, that is
closer to the polypeptide backbone, while Leu branches “farther out.”
Because α -helices are tightly packed structures with little empty space,
branching close to the backbone must sterically interfere with the backbone
being able adopt an α-helical conformation. Note: Because of the chemical
similarities between Le...
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- Winter '13