1. Unit 2: SMELLS Molecular Structure and Properties
Living By Chemistry
Unit 2: SMELLS
Molecular Structure and Properties

2. Section IV: Molecules in the Body
Lesson 20 Mirror, Mirror
Lesson 21 Protein Origami
Lesson 22 Who Nose?

3. Lesson 20: Mirror, Mirror
Mirror-Image Isomers

4. ChemCatalyst
Which of these objects looks identical in a mirror? Explain any differences.
1. glove 2. barbell
3. spring tetrahedron

5. Key Question
What are mirror-image isomers?

6. You will be able to: recognize mirror-image molecular structures
explain what it means for molecules to be superimposable
understand why mirror-image isomers have different properties

7. Prepare for the Activity
Work in groups of four.

8. Discussion Notes
Mirror-image molecules that cannot be superimposed on each other are called mirror-image isomers.
Tetrahedral molecules in which four different atoms or groups are attached to a carbon atom always have mirror-image isomers.

9. Discussion Notes (cont.)
The mirror-image isomers D-carvone and L-carvone have different smells.
The mirror-image isomers have a “handedness.”

10. Wrap Up What are mirror-image isomers?
Molecules that are not identical to their mirror image are called mirror-image isomers.
Mirror-image isomers have a “handedness,” just like a right hand and a left hand.
Mirror-image isomers can have different properties, including smell.
Molecules that have at least one carbon atom with four different atoms or groups attached to it have a mirror-image isomer.

11. Check-in
Which of these molecules will have a mirror-image isomer? Explain your reasoning.
A. CF B. CHF3 C. C(CH3)4

12. Lesson 21: Protein Origami
Amino Acids and Proteins

13. ChemCatalyst The mirror-image isomers of carvone are shown.
1. Explain how the receptor sites for D-carvone and L-carvone might be different from each other.
2. Sketch receptor sites for D-carvone and L-carvone.
Assume that the
polar side (the side
with the oxygen
atom) attaches
to the receptor
site.

14. Key Question
What is a receptor site made of?

15. You will be able to:
explain that protein molecules are chains of amino acid molecules
understand that the smell receptor sites are protein chains folded to form a receptor of a specific shape
explain the “handedness” of a smell receptor site

16. Prepare for the Activity
Work in groups of four.
Amino acid: A molecule with a carboxyl functional group and an amine functional group.
Protein: A large molecule consisting of amino acids bonded together.

17. Discussion Notes
Amino acids are molecules with a carboxyl group, COOH, and an amine group, NH2.
Amino acids can link together to form long chains called proteins.
Protein molecules fold to form pockets because of attractions between the R groups on different amino acids in the chain.

18. Wrap Up What is a receptor site made of?
Amino acids are molecules with a carboxyl group, COOH, and an amine group, NH2.
Amino acids all have mirror-image isomers. Only left-handed amino acid molecules function in the human body.
The carboxyl group from one amino acid can link with the amine group of another amino acid forming a peptide bond.

19. Wrap Up (cont.)
Proteins are long chains of amino acids linked together.
Protein molecules can fold to form smell receptor sites.

20. Check-in
Name two concepts from the Smells Unit that were used today to help you understand proteins.

21. Lesson 22: Who Nose?
Unit Review

22. ChemCatalyst
Name three items that might be on an exam covering the entire Smells Unit.
Compose a question that could be included on the exam.

23. Key Question
How is smell related to molecular structure and properties?

24. You will be able to:
ask clarifying questions regarding concepts covered in this unit
create a list of topics and concepts to study for an upcoming exam

25. Prepare for the Activity
Work in pairs.

26. Discussion Notes
The methyl salicylate molecule has structural features of both a minty molecule and a sweet molecule.

27. Check-in
Would compounds made of either of these molecules have a smell? If so, try to predict what the smell would be. Explain your reasoning.