Problem 59 - Chemistry: The Central Science in SI Units, Global Edition

Question

(a) Draw the chemical structure of a generic amino acid, using \(\mathrm{R}\) for the side chain. (b) When amino acids react to form proteins, do they do so via substitution, addition, or condensation reactions? (c) Draw the bond that links amino acids together in proteins. What is this called?

Step-by-Step Solution

Answer

A generic amino acid has the chemical structure H2N-C-COOH, with R as the side chain: H | H2N-C-COOH | R Amino acids react to form proteins via condensation reactions. The bond that links amino acids in proteins is called a peptide bond, formed between the carboxyl group of one amino acid and the amino group of another: --O-NH-- This bond connects the amino acids, releasing a water molecule in the process.

Step 1: Drawing the chemical structure of a generic amino acid

To draw the chemical structure of a generic amino acid, start with a central carbon atom called the alpha-carbon. Attach an amino group (-NH2), a carboxyl group (-COOH), and a hydrogen atom to the alpha-carbon. Finally, attach the side chain (R) to the alpha-carbon. Here is the structure: H | H2N-C-COOH | R

Step 2: Determining the reaction type that forms proteins from amino acids

When amino acids react to form proteins, they do so via condensation reactions. This is because a water molecule is released when the peptide bond is formed between the amino acids.

Step 3: Drawing the bond that links amino acids in proteins and naming it

The bond that links amino acids together in proteins is called a peptide bond. A peptide bond is formed between the carboxyl group of one amino acid and the amino group of the neighboring amino acid. A water molecule is released in this condensation reaction. Here's the representation of the peptide bond between two amino acids: H H | | H2N-C-COOH + NH2-C-COOH | | R1 R2 \ / \ / --O-NH-- The peptide bond is the O-N-H bond, which is formed by releasing the water molecule.

Key Concepts

Protein Synthesis

Protein synthesis is a vital biological process that allows our cells to build proteins, which are crucial for many bodily functions. In simple terms, protein synthesis involves creating proteins from amino acids. It happens in two main stages: transcription and translation.

• Transcription: During this stage, the DNA in a cell's nucleus is used to create messenger RNA (mRNA). This mRNA serves as a template that guides the building of proteins.


• Translation: In this stage, the mRNA moves to a cell part known as ribosomes. Here, the ribosome reads the sequence of the mRNA and translates it into a specific chain of amino acids. This chain will eventually fold into a fully functioning protein.

Protein synthesis is essential because proteins are responsible for a wide range of functions in the body, such as transporting molecules, providing structural support, and acting as enzymes to speed up chemical reactions.

Peptide Bond

A peptide bond is a special type of covalent bond that serves as the glue binding amino acids together to form proteins. It's also known as an amide bond.

• Formation: A peptide bond forms between the carboxyl group of one amino acid and the amino group of another amino acid.


• Structure: Chemically, it is represented as a bond between a carbon atom and a nitrogen atom, often shown as C-N or CO-NH.

The creation of peptide bonds is essential for building the primary structure of proteins, which is a linear chain of amino acids. When peptide bonds are formed, they do not just link the acids but also help proteins to obtain their specific shapes required for their functions.

Condensation Reaction

Condensation reactions are chemical reactions where two molecules combine to form a larger molecule while releasing a small molecule, such as water, as a byproduct. This is the same reaction type used to form peptide bonds.

• In Protein Formation: When amino acids join to form proteins, the condensation reaction involves the release of a water molecule. This occurs as the carboxyl group of one amino acid reacts with the amino group of another, forming the peptide bond.


• Role in Biology: Condensation reactions are crucial not only in protein synthesis but also in the creation of other biological molecules, such as nucleic acids and polysaccharides.

The importance of condensation reactions cannot be overstated, as they are fundamental to the formation and polymerization of small organic molecules into complex and essential macromolecules within living organisms.