Question

In Section \(22.6\), three important classes of biologically important natural polymers are discussed. What are the three classes, what are the monomers used to form the polymers, and why are they biologically important?

Short answer

The three classes of biologically important natural polymers are proteins, nucleic acids, and polysaccharides. Proteins are formed from amino acid monomers and play essential roles in various biological functions, such as cellular structure and enzyme activity. Nucleic acids, comprised of nucleotide monomers, are involved in the storage, transmission, and expression of genetic information. DNA and RNA are two types of nucleic acids with differing sugars. Polysaccharides, formed from monosaccharide monomers, serve as energy reserves and provide structural support for cells. Storage polysaccharides like starch and glycogen store energy, while structural polysaccharides like cellulose and chitin support plant cell walls and arthropod exoskeletons, respectively.

Step-by-step solution

First Class of biologically important natural polymer: Proteins

Proteins are one of the three main classes of biologically important natural polymers. They are formed by the polymerization of monomers called amino acids. Amino acids are organic compounds containing both an amino group (-NH2) and a carboxyl group (-COOH). There are 20 common amino acids found in nature that combine to form proteins. Proteins are essential for a wide variety of biological functions, including cellular structure, molecular transport, enzyme activity, cellular communication, and immune system function, among others.

Second Class of biologically important natural polymer: Nucleic acids

Nucleic acids are the second class of biologically important natural polymers. They are composed of monomers called nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base. There are two main types of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA has deoxyribose as its sugar, while RNA has ribose. Nucleic acids are involved in the storage, transmission, and expression of genetic information. DNA serves as the genetic blueprint for organisms, carrying the information needed for constructing proteins and regulating cellular processes. RNA, on the other hand, primarily functions in translating the genetic information stored in DNA into proteins during a process called protein synthesis.

Third Class of biologically important natural polymer: Polysaccharides

Polysaccharides are the third class of biologically important natural polymers. They are formed by the polymerization of monomers called monosaccharides, which are simple sugars that include glucose, fructose, and galactose. Polysaccharides can be classified into two main categories: storage polysaccharides and structural polysaccharides. Storage polysaccharides, such as starch and glycogen, serve as energy reserves for cells, providing glucose for cellular metabolism when needed. Structural polysaccharides, such as cellulose and chitin, provide structural support and protection for cells. Cellulose is the primary component of plant cell walls, while chitin forms the exoskeleton of arthropods and the cell walls of fungi.

Key concepts

Proteins and Amino Acids

Imagine the body as a complex machine with numerous parts, each essential for proper functioning. Proteins are one of those critical parts, akin to molecular workers within the body. But what are proteins made of? The answer lies in the simple building blocks known as amino acids. Amino acids link together to form long chains, which fold into intricate three-dimensional structures to become functional proteins.

Each protein's specific function is determined by its unique amino acid sequence and the resulting structure. These functions are vital for life, and they include catalyzing chemical reactions as enzymes, providing cellular structure, and regulating biological processes. To further clarify the significance of this natural polymer, consider enzymes. They are proteins that speed up chemical reactions, a process that is crucial for everything from digestion to DNA replication.

Essential Amino Acids

Of the 20 common amino acids, some are categorized as 'essential', which means the human body cannot manufacture them, and they must be obtained through diet. Proteins containing all the essential amino acids are known as 'complete proteins', typically found in animal products, quinoa, and soy.

Denaturation

It's also important to note that proteins can lose their shape, a detrimental process known as denaturation. This can be caused by changes in pH, temperature, or exposure to certain chemicals. Denatured proteins are unable to perform their biological functions, highlighting the importance of the correct structure in proteins.

Nucleic Acids, DNA, and RNA

Suppose we liken the living cell to a data center. In that center, nucleic acids, namely DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), operate as the hard drives, storing and transmitting essential information. DNA, with its famous double-helix structure, is the long-term storage unit of genetic data, dictating everything from eye color to susceptibility to certain diseases.

RNA is more like a mobile flash drive – it's a temporary copy of a certain segment of DNA that travels from the nucleus to the rest of the cell, guiding the synthesis of proteins. This process is a cornerstone of cellular function and ensures the traits encoded by DNA are exhibited in the cell's structure and behavior. Without these polymers, the blueprint for life's diversity would be lost.

Types of RNA

RNA comes in several forms, each with a specific role during protein synthesis: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). mRNA carries the genetic code from DNA, tRNA brings amino acids to the ribosome, and rRNA is a key component of the ribosome itself, the site where proteins are built.

Mutation and Repair

Moreover, consider the concept of mutations, which are changes in the DNA sequence. These can lead to alteration in protein structure and function, potentially causing disease. However, cells are equipped with DNA repair mechanisms to minimise the impact of mutations, reflecting the importance of safeguarding genetic information.

Polysaccharides, Monosaccharides, and Glucose

Step into any living organism's energy factory, and you'll find polysaccharides playing crucial roles as both energy storers and structural elements. Polysaccharides are long chains formed from simpler sugar units known as monosaccharides. The most common monosaccharide is glucose, an essential energy source for cells. When multiple glucose units join together, they form polysaccharides such as starch, glycogen, or cellulose.

Starch is the main form of stored energy in plants, while glycogen serves a similar function in animal cells. When it comes to structure, cellulose provides rigidity to plant cell walls, supporting the plant's overall structure. Imagine a building with a poor foundation; it's similar to what would happen if plants lacked cellulose – they would simply collapse.

Energy Release

The stored energy in polysaccharides can be released when necessary, through a process called hydrolysis, yielding glucose molecules that are subsequently used to produce ATP (adenosine triphosphate), the cell's energy currency.

Dietary Fiber

Furthermore, polysaccharides such as cellulose also play a role in human nutrition as dietary fiber, which aids in digestion and has been linked to a reduced risk of several chronic diseases. While we cannot digest cellulose, its presence in our diet helps with the overall health of our digestive system, exemplifying the indirect yet vital role of certain polysaccharides in human health.