Vitamins are another class of essential organic molecules that are required in small quantities for many enzymes to function and, for this reason, are considered to be co-enzymes. The omega-3 alpha-linolenic acid and the omega-6 linoleic acid are essential fatty acids needed to make some membrane phospholipids. These nutrients are termed essential nutrients, meaning they must be eaten, and the body cannot produce them. While the animal body can synthesize many of the molecules required for function from the organic precursors, there are some nutrients that need to be consumed from food. Fats are required in the diet to aid the absorption of fat-soluble vitamins and the production of fat-soluble hormones. Fatty foods are also significant sources of energy because one gram of fat contains nine calories. Fats add flavor to food and promote a sense of satiety or fullness. Excess nitrogen must be excreted as it is toxic.

The carbon and nitrogen derived from these become the building block for nucleotides, nucleic acids, proteins, cells, and tissues. Amino acids are the building blocks of proteins and protein breakdown provides amino acids that are used for cellular function. Protein catabolism provides a source of organic nitrogen. Excess digestible carbohydrates are stored by mammals in order to survive famine and aid in mobility.Īnother important requirement is that of nitrogen. Excess glycogen can be converted to fats, which are stored in the lower layer of the skin of mammals for insulation and energy storage. Glycogen stores are used to fuel prolonged exertions, such as long-distance running, and to provide energy during food shortage.

The excess sugars in the body are converted into glycogen and stored in the liver and muscles for later use. The intestinal flora in the human gut are able to extract some nutrition from these plant fibers. In humans, these molecules provide the fiber required for moving waste through the large intestine and a healthy colon. Complex carbohydrates, including polysaccharides, can be broken down into glucose through biochemical modification however, humans do not produce the enzyme cellulase and lack the ability to derive glucose from the polysaccharide cellulose. During digestion, digestible carbohydrates are ultimately broken down into glucose and used to provide energy through metabolic pathways. Carbohydrates or sugars are the primary source of organic carbons in the animal body. The organic molecules required for building cellular material and tissues must come from food.

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