Organic Chemistry : Help with Other Biological Molecules

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #1 : Help With Other Biological Molecules

Which of the following can be classified excluisively as pyrimidines?

Possible Answers:

Cytosine and thymine

Adenine and thymine

Cytosine and guanine

Adenine and guanine

Correct answer:

Cytosine and thymine

Explanation:

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

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Consider the DNA bases cytosine and guanine. Which interaction allows for these bases to pair up and form a double helix?

Possible Answers:

Nitrogen bonding

Covalent bonding

Dipole-dipole interactions

Hydrogen bonding

Correct answer:

Hydrogen bonding

Explanation:

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

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A chair flip of the pictured cyclohexane would result in __________.

Possible Answers:

all three substituents 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

the bromine in the axial position and both the chlorine and alcohol in the equatorial position

Correct answer:

the bromine in the equatorial position and both the chlorine and alcohol in the axial position

Explanation:

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?

Possible Answers:

Carbon

Nitrogen

Phosphorous

Oxygen

Correct answer:

Carbon

Explanation:

By definition, an organic compound is a compound that contains carbon. Organic chemistry is the study of carbon-containing molecules.

Example Question #5 : Help With Other Biological Molecules

Which of the following compounds are isomers?

Possible Answers:

1-butanol and 2-butanol

Benzene and hexane

Methane and methanol

Ethane and ethanol

Correct answer:

1-butanol and 2-butanol

Explanation:

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 #6 : Help With Other Biological Molecules

By which characteristic do resonance structures of a molecule differ?

Possible Answers:

Rotation around sigma bonds

Molecular formula

Hybridization

The position of the electrons

Correct answer:

The position of the electrons

Explanation:

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 #7 : Help With Other Biological Molecules

Which of the atoms in the molecules below is/are sp2 hybridized?


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Possible Answers:

1 and 5

3 only

1 and 4

1, 3 and 5

2 and 4

Correct answer:

1, 3 and 5

Explanation:

The boron in 2 is sp3 hybridized because of its four  substituents and the carbon in 4 is sp hybridized because of its connection to only the nitrogen with a single .

Example Question #8 : Help With Other Biological Molecules

Pinene

How many isoprene units does the given molecule, alpha-pinene, have?

Possible Answers:

None - it is not a terpene

Correct answer:

Explanation:

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 #9 : Help With Other Biological Molecules

Cholic acid 3d

What class of biological molecule is the given compound? 

Possible Answers:

Fatty acid

Steroid

Amino acid

Nucleic acid

Carbohydrate

Correct answer:

Steroid

Explanation:

This is cholic acid, a steroid.  Steroids can be easily identified by their characteristic fused ring structures.

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