Question

Describe the range of molar masses shown by proteins in the body. Are such molar masses consistent with proteins being polymers?

Short answer

The molar mass range of proteins in the body varies from a few thousand g/mol (e.g., insulin with a molar mass of around 5700 g/mol) to several million g/mol (e.g., titin with a molar mass of about 3,000,000 g/mol). This wide range of molar masses, along with the structure of proteins being made up of repeating amino acid residues, supports the classification of proteins as polymers.

Step-by-step solution

Molar Mass Range of Proteins

Proteins are made up of amino acid residues that are linked together in a chain-like structure. The molar mass of a protein is the sum of the molar masses of the individual amino acids. The mass of an amino acid residue typically ranges from 75 g/mol to 150 g/mol. The smallest proteins in the body contain around 50 amino acid residues, while the largest proteins may consist of thousands of residues. Therefore, the molar mass range of proteins in the body can be from approximately a few thousand g/mol (e.g., insulin, which has a molar mass of around 5700 g/mol) to several million g/mol (e.g., titin, a protein with a molar mass of about 3,000,000 g/mol).

Consistency with Proteins Being Polymers

The term "polymer" refers to a molecule made up of many smaller repeating units called monomers. In the case of proteins, the monomers are amino acid residues. The wide range of molar masses found in proteins supports the idea that they are polymers, as the number of repeating amino acid residues can vary greatly between different proteins. As we previously mentioned, the molar mass of a protein is determined by the total number of amino acid residues it contains, as well as the molar mass of each residue. Given the large variation in protein sizes in terms of the number of amino acids, it is logical to consider proteins as polymers. In conclusion, the molar mass range of proteins in the body varies from a few thousand g/mol to several million g/mol. This wide range of molar masses and the structure of proteins, which are made up of repeating amino acid residues, support the classification of proteins as polymers.

Key concepts

Amino Acid Residues

Proteins are the workhorses of cells, taking part in virtually every cellular process. To understand how proteins achieve such varied functionality, one must begin at the smallest unit of a protein's structure: the amino acid residues. Amino acid residues are essentially amino acids less one water molecule, which is lost during the formation of peptide bonds. Each residue has a unique side chain, termed an R-group, which determines the chemical properties and potential interactions the amino acid can engage in.

There are twenty standard amino acids, each with its own specific mass and characteristics. Though they typically have a mass ranging between 75 g/mol and 150 g/mol, these small differences can have a profound impact on the overall structure and function of the protein. When amino acids link together, they form long chains called polypeptides, through a process known as dehydration synthesis. In this reaction, a water molecule is released, hence the term 'residue' for the remaining part incorporated into the chain.

Protein Polymers

Understanding protein polymers is essential when delving into the molar mass of proteins. Just as a train consists of a series of cars linked together, protein polymers are chains of amino acid residues connected end-to-end. This arrangement forms the primary structure of a protein, which can then fold into more complex shapes necessary for the protein's function.

The vast array of shapes and sizes proteins can assume is due to the sequence of amino acid residues in the chain -- a sequence that is meticulously encoded in our DNA. Proteins can range from small hormones that carry signals between cells, like insulin, to massive structural components, such as titin, which gives muscles their elasticity. This incredible variability in size and structure is why proteins can have molar masses varying from a few thousand to several million g/mol. When considering this immense variety, it becomes clear that proteins are indeed polymers since they are structured as a series of repeating units that create an even larger molecule.

Monomers and Polymers

When discussing monomers and polymers, it's beneficial to look towards everyday analogies. A monomer is akin to a single brick, while a polymer is the entire wall constructed from those bricks. In protein chemistry, the 'bricks' are the amino acid residues, and the 'wall' is the complete protein structure formed when these monomers connect through peptide bonds.

Monomers relate to polymers as both the building blocks and the resulting structure. In proteins, the sequence and type of amino acid residues (monomers) determine the protein's properties and function (polymer). This concept is central to macromolecular science, where understanding how the monomeric units relate to the entire structure is fundamental for grasping how biological molecules work. Through this lens, it becomes feasible to comprehend why proteins, though composed of similar building blocks, can function so diversely in living organisms.