Glaser's "Chemistry is in the News"
To Accompany Wade Organic Chemistry 4/e.
Chapter 24. Amino Acids, Peptides, & Proteins.

Editorial Comments

Proteins are one of the most abundant organic molecules found in humans and animals.  They come in many different forms, including structural, enzyme, and carrier.  Proteins perform a variety of different functions in the body, ranging from photosynthesis in plants, to composing hair and fingernails, to acting as a catalyst for reactions such as DNA replication and repair.

The building blocks of proteins are amino acids held together by peptide bonds.  They are composed of amino acid backbones and varying side chains (which contain the functional groups).  A peptide bond incorporates the carboxyl group of one amino acid and the amino group of another through dehydration synthesis.

There are twenty standard amino acids, ten of which can be synthesized by the body (the other ten must be consumed).  The ones produced by the body are known as the non-essential amino acids.  Of the ten essential amino acids that must be consumed in the diet, tryptophan is associated with some of the brain's functions.  Its functional group is indole, which is a fused heterocyclic compound with one amino group in the ring.  Take a look at the biosynthesis pathway for the production of this molecule. (Also see this chime animation of L-tryptophan.) Tryptophan is a precursor to serotonin, a vital neurotransmitter found to affect pain, sleep, mood, and appetite.

Bulimia is an eating disorder that has become increasingly common in past decades.  It involves binge eating (consuming very large amounts of food at one time) and purging (induced vomiting).  It may also include using laxatives, weight loss drugs, and  excessive exercising.  This disease occurs in about 2-3% of the population and is especially prevalent in young women trying to fit into societyís stereotype of beauty.  Therefore, it is important that one knows the symptoms and causes of bulimia so that it can be spotted in a friend or loved one.  Please take a look at this fact sheet from New York Online Access to Health, as it provides a concise overview of bulimia.  Bulimia has often been thought of as a disease triggered by societyís emphasis on beauty, low self esteem, or peer pressure.  However, new research shows that there might be chemical/biological factors involved in the disorder.

This article about the study at the University of Oxford (UK) supports the hypothesis that decreased serotonin activity in the brain may be the cause of mood disturbances and mental illnesses associated with bulimia.  Also, it appears that a vicious cycle may form whereby due to consistent dieting, an individual may deprive themselves of essential tryptophan, thus leading to additional eating disorders and losses of tryptophan.
 

Pertinent Text References
Chapter 24. Amino Acids, Peptides, & Proteins.
 

Questions

Question 1: In the study mentioned in the article, ten former bulimics and twelve normal women were involved. Does a sample of twenty-two women constitute a large enough study for researchers to make definite statements? What else could researchers do to verify the accuracy of this study?

Answer: (a) No. A larger sample size is needed.
(b) Study children and follow them for a period of time to see if they develop bulimia or remain normal. -or- etc.

Question 2: Does the findings of this study confirm or disprove traditional beliefs that bulimia is solely a psychological illness?  What are other possible reasons for bulimia?

Answer: Disprove. Other causes: personality, genitic and environmental factors, biochemistry, etc...

Question 3: What new support has been found for the hypothesis that a chemical malfunction in the brain contributes to bulimia?

Answer:  Women who have recovered from bulimia are more affected by a deprivation of tryptophan than women who have never had an eating disorder.

Question 4: L-Tryptophan is the essential amino acid that has been shown in this study to be linked to bulimics.  Amino acids are covered in chapter 24 of the text, and L-Tryptophan is shown on page 1122.  What are the two functional groups on L-tryptophan that make it an amino acid?

Answer: The amine (-NH₂) and the carboxyl (-COOH) groupsdetermine that L-tryptophan is an amino acid.

Question 5: Briefly skim the introduction of this scientific report about serotonin to learn its importance in humans.  Then take a look at this diagram, from Professor Curtis Loer of the University of San Diego, which shows the synthesis pathway in which tryptophan is converted into serotonin.  (a) What functional group is added to the aromatic ring?  (b) Which functional group serves as a leaving group from the amino acid?

Answer:(a) An alcohol group (-OH) is added to the aromatic ring.
(b) A carboxyl group (-COOH) serves as a leaving group, leaving from the amino acid.

Question 6:  Serotonin is believed to be the chemical behind many common mental disorders.  Do you think that the government should put more money into the research of this chemical and the way it affects mental disorders?  Do you think that new drug regimes and gene therapies could be developed from further research or do you think that it would be a scientific dead end to pursue this line of research?

Answer:  Yes, scientific research should be allotted more money.  This is an important issue that affects many people and offers a realm of possibilities in the development of drug regimes and gene therapies.