Daria Z. Hall

Lesson Plan 1: Peptides and Proteins

Dr. Thornton

Chem 504 - Biochemistry

Objectives:

• Students will be able to identify the functional groups and locations that define an

amino acid

• Students will be able to identify amino acids by their R groups

• Students will be able to illustrate a peptide bond and show the resulting peptide

Target Audience:

This lesson is directed toward a college prep chemistry class with a length of

approximately 45 minutes. These students will already be familiar with the standard line

angle method of drawing organic molecules as well as Lewis structures and the shortcuts

(only showing carbon-carbon, not hydrogens).

Lesson:

As the students enter, give them the sheet labeled Appendix 1. It contains the structures

of the 20 common amino acids. Ask the students to work in pairs to identify

commonalities between these structures.

Students should identify the COOH and the NH2 ligands off of the alpha carbon.

Essentially, they should be able to identify that the molecules are the same except for one

ligand on the alpha carbon. The one exception that might be noted is proline.

At this point, discussion should begin about the definitions of amino acid, peptides,

proteins, etc. using the following definitions.

Amino acid: organic compound containing at least one amino group and one carboxylic

acid group - the basic building block of proteins. Additionally, each amino acid contains

an “R” group, which is There are 20 of these that are used in protein synthesis. Eight of

these can be produced by the human body; the remaining twelve need to be consumed via

diet. These are referred to as essential amino acids.

http://www.biology.lsu.edu/webfac/dlongstreth/biol12014f02/lectur12.jpg (accessed

7/04/07)

Amino group: NH2 (shown in yellow above)

Carboxylic acid group: COOH (shown in blue above)

At this point, give the students the selection of amino acids provided in Appendix 2. Ask

them to work in small groups to identify the amino acids by using the “R” groups.

The answers for the worksheet are as follows, if you choose to review this in class.

1. glycine 2. cysteine 3. leucine 4. phenylalanine 5. tryptophan

Peptide: any one of a variety of short molecules formed by the combination of various

amino acids – so whenever one amino acid bonds to another, a peptide is formed.

Peptide bond: a chemical bond formed between amino acids. This occurs when the

carboxyl group of one amino acid reacts with the amino group of another amino acid.

When this occurs, water is a product in addition to the peptide. This is also known as a

condensation reaction.

Illustration of peptide bond formation. This could either be used for a template to

work on the blackboard or as an overhead. Ask the students to help identify which atoms

are involved in the formation of water.

Taken from http://courses.cm.utexas.edu/emarcotte/ch339k/fall2005/Lecture-Ch3-

1/Slide18.JPG (accessed 7/04/07)

Protein: large organic molecules formed from multiple peptides. These arrange

themselves into various shapes and subunits.

Students should now begin to work on the worksheet labeled Appendix 3. This asks

them to draw the peptide results of the combination of two, three, or four amino acids.

This will probably need to be completed for homework. An answer key is provided

following Appendix 3.

Appendix 1:

Amino Acid Symbol Structure*

Amino Acids with Aliphatic R-Groups

Glycine Gly - G

Alanine Ala - A

Valine Val - V

Leucine Leu - L

Isoleucine Ile - I

Non-Aromatic Amino Acids with Hydroxyl R-Groups

Serine Ser - S

Threonine Thr - T

Amino Acids with Sulfur-Containing R-Groups

Cysteine Cys - C

Methionine Met-M

Acidic Amino Acids and their Amides

Aspartic Acid Asp - D

Asparagine Asn - N

Glutamic Acid Glu - E

Glutamine Gln - Q

Basic Amino Acids

Arginine Arg - R

Lysine Lys - K

Histidine His - H

Amino Acids with Aromatic Rings

Phenylalanine Phe - F

Tyrosine Tyr - Y

Tryptophan Trp-W

Imino Acids

Proline Pro - P

Taken and modified from http://www.indstate.edu/thcme/mwking/amino-acids.html

(accessed 7/3/07)

Appendix 2:

Name: ____________________________________________

Peptides and Proteins 1

Using the table of amino acids, identify the following amino acids.

1.

2.

3.

4.

5.

Appendix 3:

Name: __________________________________________

Peptides and Proteins 2

For each of the following sets of amino acids, first draw the amino acids, then draw the

peptides formed when the amino acids bond.

1. Ala – Gly

2. Val – Thr

3. Asp – Phe – Ser

4. Tyr – Leu – Cys

5. Ser – Cys – Thr – Val

6. Lys – Gly – Ile – Phe

Summary:

The students should be able to draw a generic line angle structure for a peptide of up to

four amino acids, using R to represent the various R groups that are individual for each

amino acid. They might want to use the homework (Appendix 3) and notes for peptide

bond formation for help. It is highly recommended to have the students check each

others work and perhaps share answers with the class.

References for images for Appendix 2

http://commons.wikimedia.org/wiki/Image:Glycine.png

http://en.wikipedia.org/wiki/Cysteine

http://en.wikipedia.org/wiki/Leucine

http://upload.wikimedia.org/wikipedia/commons/2/29/Mol2d.L.Phenylalanine.png

http://sense-datum.org/tim/images/tryptophan.jpg

all accessed 7/04/07