Problem 11 - Chemistry: An Atoms-Focused Approach

Question

In living cells, amino acids combine to make peptides and proteins. Are these processes accompanied by increases or decreases in the entropy of the reaction system?

Step-by-Step Solution

Answer

Answer: The processes of amino acids combining to make peptides and proteins result in a decrease in entropy of the reaction system, as the system becomes more ordered.

Step 1: Define entropy

Entropy is a measure of the degree of disorder in a system. In a chemical reaction, an increase in entropy indicates a more disordered system, while a decrease in entropy indicates a more ordered system. More disordered systems are thermodynamically favored.

Step 2: Understand the process of polypeptide and protein formation

In living cells, amino acids combine to form polypeptides and proteins through a process called the peptide bond formation, also known as the condensation reaction. In this process, the carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH2) of another amino acid, releasing a water molecule (H2O) and forming a peptide bond.

Step 3: Evaluate the change in entropy during peptide bond formation

During the peptide bond formation, two amino acids combine and become more ordered as they form a single peptide molecule. The release of a water molecule also occurs during this process. The system becomes more ordered, with a single polypeptide molecule being formed from two separate amino acids.

Step 4: Determine whether the process increases or decreases entropy

As the formation of peptides and proteins from amino acids results in a more ordered system, the overall entropy of the reaction system decreases. So, the processes of amino acids combining to make peptides and proteins are accompanied by a decrease in entropy.

Key Concepts

Amino Acids

Amino acids are the building blocks of proteins, vital to various functions in living organisms. Structurally, each amino acid contains an amino group

• (-NH₂)
• a carboxyl group (-COOH)
• and a unique side chain (R group) that determines its specific properties.

The variation in the R group is what gives rise to the 20 standard amino acids found in proteins.

Living organisms use a genetic code to arrange amino acids into proteins. These proteins perform diverse roles, from catalyzing biological reactions (enzymes) to providing structural support and regulating immune function.

Understanding amino acids is fundamental to grasping how proteins function and interact within cells. This knowledge is critical for studying cellular processes and designing interventions for disease management and therapy.

Peptide Bond Formation

Peptide bond formation is an essential process in biology, resulting in the creation of polypeptides and proteins. This reaction is also known as a condensation reaction because it involves the combination of molecules with the removal of a water molecule.

During this process, the carboxyl group of one amino acid reacts with the amino group of another. This reaction forms a covalent bond called a peptide bond, specifically (-CO-NH-), linking the two amino acids together into a dipeptide.

Peptide bonds are strong and stable, which is crucial for maintaining the integrity of protein structures.

• This formation reduces entropy, as two separate molecules become one, leading to a more ordered system and releasing water in the process.

Understanding peptide bond formation is key to comprehending how proteins are synthesized and how they achieve their functional conformations.

Protein Synthesis

Protein synthesis is the process of building proteins from amino acids, occurring in a series of steps within the cell. This complex process involves two main phases:

• transcription
• and translation.

Transcription takes place in the nucleus, where a DNA segment (gene) is used as a template to produce messenger RNA (mRNA).

This mRNA travels to the ribosome, the cellular machinery for protein synthesis. Here, the process of translation occurs – the mRNA sequence is read in sets of three nucleotides (codons), each specifying a particular amino acid.

Transfer RNA (tRNA) brings the appropriate amino acid to the ribosome, where they are assembled sequentially into a growing polypeptide chain through the formation of peptide bonds.

• The chain eventually folds into a functional protein, with its specific three-dimensional structure necessary for its particular biological activity.

Understanding protein synthesis is crucial for appreciating how genetic information manifests as functional cellular components.