Organic Chemistry : Help with Other Biological Molecules
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Example Questions
Example Question #1 : Help With Other Biological Molecules
Which of the following can be classified excluisively as pyrimidines?
Cytosine and thymine
Adenine and thymine
Cytosine and guanine
Adenine and guanine
Cytosine and thymine
Pyrimidine is one classification of a nucleotide base that is formed of only one six-membered heterocyclic ring. Cytosine and thymine (of DNA) and uracil (of RNA) are all pyrimidines while adenine and guanine are classified as purines. One way to help you remember this is that pyrimidines, like pyramids, are "sharp." Sharp things "CUT" Cytosine, Uracil, Thymine.
Example Question #2 : Help With Other Biological Molecules
Consider the DNA bases cytosine and guanine. Which interaction allows for these bases to pair up and form a double helix?
Dipole-dipole interactions
Covalent bonding
Nitrogen bonding
Hydrogen bonding
Hydrogen bonding
The correct answer is hydrogen bonding. The hydrogens on the amine groups of each base can hydrogen bond with the nitrogens and oxygens in the adjacent base. Three hydrogen bonds are formed between cytosine and guanine, and these three bonds are what make up the "rungs" of the ladder, that is the DNA double helix.
Example Question #3 : Help With Other Biological Molecules
A chair flip of the pictured cyclohexane would result in __________.
the bromine in the axial position and both the chlorine and alcohol in the equatorial position
all three substituents in the axial position
the bromine in the equatorial position and both the chlorine and alcohol in the axial position
all three substituents in the equatorial position
the bromine in the equatorial position and both the chlorine and alcohol in the axial position
Originally, bromine is in the axial position and the other two substituents are equatorial. During a chair flip, all substituents become inverted in their positions. Therefore, the bromine will be found in the equatorial position and both the chlorine and alcohol will be found in the axial position.
Example Question #4 : Help With Other Biological Molecules
Which element is present in all organic compounds?
Phosphorous
Nitrogen
Oxygen
Carbon
Carbon
By definition, an organic compound is a compound that contains carbon. Organic chemistry is the study of carbon-containing molecules.
Example Question #4 : Help With Other Biological Molecules
Which of the following compounds are isomers?
1-butanol and 2-butanol
Ethane and ethanol
Methane and methanol
Benzene and hexane
1-butanol and 2-butanol
By definition, isomers are compounds that share the same molecular formula but have differing molecular structures. 1-butanol and 2-butanol share the same formula, but the hydroxyl group can be located on either the first or second carbon on the molecule, yielding two different structures that share the same molecular formula. The other answers have different molecular formulas and are thus not isomers.
Example Question #5 : Help With Other Biological Molecules
By which characteristic do resonance structures of a molecule differ?
The position of the electrons
Hybridization
Rotation around sigma bonds
Molecular formula
The position of the electrons
By definition, resonance structures are multiple Lewis structures that depict the same molecular compound. The only difference pertains to the way in which electrons are shared by atoms in the molecule. Molecules are weighted averages of their most stable resonance contributors.
Example Question #6 : Help With Other Biological Molecules
Which of the atoms in the molecules below is/are sp2 hybridized?
2 and 4
3 only
1 and 5
1, 3 and 5
1 and 4
1, 3 and 5
The boron in 2 is sp3 hybridized because of its four 
Example Question #7 : Help With Other Biological Molecules
How many isoprene units does the given molecule, alpha-pinene, have?
None - it is not a terpene
Alpha-pinene is a terpene, and is thus composed of isoprene units. A single isoprene unit has 5 carbon atoms. This molecule has 10 carbons, thus it contains 2 isoprene units.
Example Question #8 : Help With Other Biological Molecules
What class of biological molecule is the given compound?
Amino acid
Nucleic acid
Steroid
Fatty acid
Carbohydrate
Steroid
This is cholic acid, a steroid. Steroids can be easily identified by their characteristic fused ring structures.
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