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Ch.18 Amino Acids and Proteins
McMurry - Fundamentals of General, Organic, and Biological Chemistry 8th Edition
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Non è quello che usi tu?Cambia libro di testo
Capitolo 18, Problema 62

The endorphins are a group of naturally occurring neurotransmitters that act in a manner similar to morphine to control pain. Research has shown that the biologically active parts of the endorphin molecules are simple pentapeptides called enkephalins. Draw the structure of the methionine enkephalin with the sequence Tyr-Gly-Gly-Phe-Met. Identify the N-terminal and C-terminal amino acids.

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Step 1: Understand the structure of a peptide. A peptide is a chain of amino acids linked by peptide bonds. Each amino acid has an amino group (-NH₂), a carboxyl group (-COOH), and a unique side chain (R group). The peptide bond forms between the carboxyl group of one amino acid and the amino group of the next.
Step 2: Write the sequence of the peptide. The given sequence is Tyr-Gly-Gly-Phe-Met. This means the peptide starts with Tyrosine (Tyr) and ends with Methionine (Met). Each amino acid is connected by peptide bonds in the order provided.
Step 3: Identify the N-terminal and C-terminal amino acids. The N-terminal amino acid is the one with the free amino group (-NH₂) at the start of the sequence, which is Tyrosine (Tyr). The C-terminal amino acid is the one with the free carboxyl group (-COOH) at the end of the sequence, which is Methionine (Met).
Step 4: Draw the structure of the peptide. Start with the N-terminal Tyrosine (Tyr), followed by Glycine (Gly), another Glycine (Gly), Phenylalanine (Phe), and finally Methionine (Met). Ensure that each amino acid is connected by a peptide bond (-CO-NH-). Include the side chains for each amino acid: Tyr has a phenol group, Gly has a hydrogen atom, Phe has a benzyl group, and Met has a thioether group.
Step 5: Verify the structure. Check that the peptide chain is correctly drawn with the proper sequence, peptide bonds, and side chains. Confirm that the N-terminal (Tyr) has a free amino group and the C-terminal (Met) has a free carboxyl group.

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Endorphins and Enkephalins

Endorphins are neurotransmitters produced by the body that help relieve pain and induce feelings of pleasure. Enkephalins are a specific type of endorphin, consisting of short chains of amino acids known as peptides. They bind to opioid receptors in the brain, mimicking the effects of morphine and playing a crucial role in pain modulation.

Amino Acid Structure

Amino acids are the building blocks of proteins, each consisting of a central carbon atom, an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group). The sequence of amino acids in a peptide determines its structure and function. In the context of enkephalins, the specific sequence of amino acids influences their ability to bind to receptors and exert biological effects.
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N-terminal and C-terminal

In a peptide or protein, the N-terminal refers to the end of the molecule that has a free amino group (-NH2), while the C-terminal is the end with a free carboxyl group (-COOH). Identifying these terminals is essential for understanding the directionality of the peptide chain, which is crucial for its synthesis and function. In methionine enkephalin, the N-terminal is Tyrosine (Tyr) and the C-terminal is Methionine (Met).
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