MCAT Biology : Organic Analyses and Lab Techniques
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Example Question #51 : Organic Analyses And Lab Techniques
Which of the following properties can be used to differentiate between enantiomers?
Melting temperature
Heat of vaporization
Optical activity
Density
Optical activity
Chiral molecules are a unique type of isomer, defined as two molecules with inverted stereochemistry, which makes them mirror images of one another. These isomers will ahve the same molecular weight, as well as most physical properties. Enatiomers cannot be distinguished based on melting point, heat of vaporization, or density. The primary, defining characteristic of a chiral molecule is its ability to effect plane polarized light. One isomer will rotate the light to the right, while the other will rotate the light to the left.
Example Question #52 : Organic Analyses And Lab Techniques
Which of the following properties cannot be used to differentiate between myoglobin and hemoglobin?
Location
Affinity for oxygen
Bound reduced iron
Number of subunits
Bound reduced iron
Myoglobin and hemoglobin are the proteins primarily responsible for binding, transporting, and storing oxygen. Myoglobin is primarily located in muscle tissue, and has a very high affinity for oxygen. Hemoglobin is located in the blood, and has a slightly lower oxygen binding affinity. Thus, as hemoglobin carries oxygen past muscle tissue, oxygen can be released and will preferentially bind to myoglobin. Hemoglobin contains four subunits, each capable of binding one oxygen molecule, while myoglobin consists of only one subunit.
Both hemoglobin and myoglobin contain heme units, which structurally and functionally rely on the incorporation of reduced iron. As such, this property cannot be used to differentiate these two proteins.
Example Question #3 : Other Techniques
Which macromolecule is classified by physical properties rather than by monomer?
Lipids
Nucleic acids
Proteins
Carbohydrates
Lipids
Unlike carbohydrates, proteins, and nucleic acids, lipids do not have a uniform monomer structure. Rather, they are classified by their hydrophobic properties and a variety of beasic structural categorizations. Some examples of lipid classifications are glycerophospholipids, sphingolipids, and steroids.
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