Proteins, also called enzymes, are the body's "building blocks." They are made of long sequences of amino acids, called polypeptides, which form different types of proteins. One polypeptide sequence may create collagen and muscle fibers. Another turns into keratin, the material of hair and fingernails. A third sequence can become hemoglobin, the blood molecules that carry oxygen and vital nutrients through the circulation system. Organism cells build millions of different proteins, each designed for a highly specific function. A protein often act as a catalyst, prompting biological reactions and processes.They also help regulate hormones, such as insulin, to maintain blood sugar levels.
Nucleic acids consist of two types of organic molecules: DNA and RNA. They contain the genetic information required to build proteins and create new cells. Nucleic acids are highly complex molecules made from nucleotides. A nucleotide is made from a five-carbon sugar, one or more phosphate groups and a ring-shaped molecule called a purine or pyrimidine. Each nucleotide binds with another to create the characteristic double-helix shape of DNA. Nucleic acids encode or read genetic information. DNA acts as a cellular database, containing millions of "recipes" to build proteins and new cells. RNA can "read" the recipe to produce the proteins and structures, which eventually become the cell's building blocks.
Carbohydrates are organic compounds that only consist of carbon, hydrogen and oxygen. Their function is to provide energy for cells and organisms. Carbohydrates break down into a few classes. The simplest forms are called monosaccharides. These small simple molecules include glucose and fructose. Complex, linked chains are called polysaccharides, such as starch and glycogen. Animal and human cells store glycogen and other polysaccharides, and break them down into glucose or fructose when they need energy.
Lipids are fatty acid esters that are responsible for cell structure and energy reserves. Fat, lard, oils, steroids and wax are all classified as lipids, because they are not entirely water soluble. Cell membranes contain lipids to maintain their semi-permeable structure. Lipids also store energy in the form of body fat. Unlike carbohydrates, which break down quickly and provide short-term energy, lipids are designed to contain energy for long periods. When carbohydrates are not available, the body can converts lipids to use as energy. Lipids also provide insulation from the cold, absorb shocks and regulate some cell functions.