Macromolecules

Covalent bonding can create larger molecules and many molecules fall into 4 different categories of macromolecules: lipids, carbohydrates, nucleic acids, and proteins.

Lipids

The first macromolecule category we will discuss is lipids. Lipids are generally non-polar and therefore do not interact easily (we will discuss a molecule that does not adhere to this below). In this class, we will discuss 3 main categories of lipids although other chemistry courses will likely discuss others as well. Triglycerides are commonly are referred to as "fat" and are used in the body to store energy as well as insulate the body and pack organs. Triglycerides are hydrophobic.

The second category of lipids is phospholipids and cell membranes are composed primarily of phospholipids (more on this in another module). Phospholipids are unique lipids because they are amphipathic which means they have both polar and non-polar regions.

The third category is steroids which mostly act as signaling molecules (hormones). These molecules are produced from cholesterol and you've probably heard of several including testosterone, estrogen, and cortisol. If not, don't worry, you will learn about them in BIO 141.

Cholesterol

A note on monomers and polymers

The remaining 3 categories have a monomer/polymer relationship meaning that monomers are small building blocks that combine to form polymers as shown in the image below.

Carbohydrates

The monomer of a carbohydrate is a monosaccharide and the polymer is a polysaccharide. The monosaccharides are simple sugar molecules such as glucose and fructose which taste sweet. Monosaccharides can combine to produce disaccharides such as sucrose (white sugar) or lactose (milk sugar) which also taste sweet. Monosaccharides can combine to produce much larger molecules that are not sweet called polysaccharides such as starch (produced by plants) and glycogen which is the only polysaccharide humans produce and are found in skeletal muscle and liver cells and can be composed of upwards of 60,000 glucose molecules.

Carbohydrates are primarily used for energy and are the molecules the body uses first as a source of energy. Polysaccharides are a storage form of energy and must be broken down to monosaccharides before cells can produce energy from them.

Nucleic Acids

Nucleic acids have a monomer of nucleotides which combine to form DNA (deoxyribonucleic acids) and RNA (ribonucleic acids). Adenosine triphosphate (ATP) is also a nucleotide that cells use as energy to do cellular work (more on this in the next module).

DNA is the genetic material that is passed from one generation to the next and is a set of genes (recipes) that code for proteins. RNA comes in several forms, but is generally involved in protein synthesis.

Although we will not go into detail in this course, you have probably heard of nucleotides if you have taken a biology course before and remember their abbreviations: A, C, T, G, and in RNA, U.

DNA and the nitrogenous base monomers

Proteins

Proteins are a diverse structural group and therefore, have diverse functions. The monomer for protein is the amino acid of which 20 have been identified. Cells combine these amino acids in the appropriate order (as dictated by DNA) to create the linear form of a protein. Proteins then fold upon themselves to create a secondary level of structure. These proteins further fold upon themselves to create a tertiary level of structures. For many proteins, the protein is fully functional after the tertiary level of structure, but others require several proteins to combine to become fully functional which is termed quaternary level of structure. One VERY important concept here is that structure of a protein is extremely important. If you change the structure slightly, it will change the function or even become non-functional.

As stated above, the structure of a protein is very important to its function. Proteins have diverse functions and can function as enzymes, transport proteins, contractile proteins, structural proteins, signaling proteins, defense proteins, and storage proteins. All of these will be addressed in this course or in BIO 141 and 142.

The structure is extremely important for protein functions, but this structure could be permanently changed by denaturation. Denaturation is the result of high temperatures (high fevers) or high or low pH.