Problem 62 - Chemistry The Central Science

Question

Write a chemical equation for the formation of methionyl glycine from the constituent amino acids.

Step-by-Step Solution

Answer

The chemical equation for the formation of methionyl glycine from methionine and glycine is: \(CH_3-S-CH_2-CH_2-CH(NH_2)-COOH + H_2N-CH_2-COOH \rightarrow CH_3-S-CH_2-CH_2-CH(NH-CH_2-COOH)-CO-NH_2+ H_2O\)

Step 1: Identify the amino acids involved

The two amino acids involved in the formation of methionyl glycine are methionine and glycine. Methionine has the chemical structure: \[CH_3-S-CH_2-CH_2-CH(NH_2)-COOH\] and glycine has the chemical structure: \[H_2N-CH_2-COOH\]

Step 2: Peptide bond formation

The peptide bond formation occurs between the carboxyl group (-COOH group) of one amino acid and the amino group (-NH₂ group) of the other amino acid. In this case, the peptide bond will form between the carboxyl group of methionine and the amino group of glycine. When this bond is formed, water (H₂O) is released as a by-product.

Step 3: Write the chemical equation

Now that we know the structures of the amino acids and how they form a peptide bond, we can write the chemical equation for the formation of methionyl glycine: \[CH_3-S-CH_2-CH_2-CH(NH_2)-COOH + H_2N-CH_2-COOH \rightarrow CH_3-S-CH_2-CH_2-CH(NH-CH_2-COOH)-CO-NH_2+ H_2O\] This chemical equation shows the formation of methionyl glycine from methionine and glycine through the peptide bond formation and release of water.

Key Concepts

Amino Acids

Amino acids are the building blocks of proteins, each with a unique structure and property. Essentially, they are organic compounds composed of a central carbon atom attached to an amino group (-NH_2), a carboxylic acid group (-COOH), a hydrogen atom, and a distinctive side chain, often denoted as 'R'. The side chain differs between amino acids and determines their physical and chemical properties.

There are twenty standard amino acids, each playing a specific role in the body. For instance, some may provide structural elements, whereas others play a role in metabolism. Methionine and glycine, mentioned in the exercise, are two basic amino acids. Methionine is known for its sulfur-containing side chain, while glycine is the simplest amino acid, with just a hydrogen atom as its side chain. Understanding the structure of these amino acids is crucial when examining peptide bond formation and protein synthesis.

Protein Synthesis

Protein synthesis is a fundamental biological process by which individual cells construct proteins. The process consists of two main steps: transcription and translation. During transcription, the genetic code from DNA is transferred to messenger RNA (mRNA) inside the cell nucleus. Following transcription, mRNA travels to the ribosome, the cellular 'machine' that reads the RNA sequence and translates it into a polypeptide chain — a sequence of amino acids.

At the ribosome, transfer RNA (tRNA) brings in amino acids that match the codons (specific sequences of three nucleotides) on the mRNA strand. Amino acids are then linked together via peptide bonds to form a polypeptide chain, ultimately folding into a functional protein. The formation of these peptide bonds is a result of a dehydration synthesis reaction, where a molecule of water is released as a by-product, as seen in the given chemical equation.

Chemical Equation

A chemical equation provides a symbolic representation of a chemical reaction. It details the reactants (substances that start a chemical reaction) on the left side and the products (substances that are produced by a chemical reaction) on the right. The arrow in between symbolizes the direction of the reaction.

Regarding peptide bond formation, the chemical equation in the exercise exemplifies the reactants (methionine and glycine) and the product (methionyl glycine) with water as the by-product. It provides a clear and simplified overview of how two amino acids are connected via a peptide bond, releasing water molecules, a process crucial to building polypeptides and, eventually, functional proteins. This process of forming a bond while eliminating water is known as condensation, an essential aspect of this chemical equation.