Final answer:
The amount and ratio of essential amino acids in a protein are crucial for its nutritional value, with some being complete and others incomplete based on their amino acid content. Animal proteins generally offer a complete array of essential amino acids, unlike some plant proteins. Essential amino acids must be provided through the diet as they cannot be synthesized by the body.
Step-by-step explanation:
The amount and ratio of essential amino acids present in a protein are indicators of the protein's nutritional value to humans. Proteins are vital for body repair and growth, especially in children, and are composed of 20 standard amino acids. Out of these, approximately half cannot be synthesized by the human body and are thus termed essential amino acids. These include methionine, valine, isoleucine, leucine, phenylalanine, histidine, lysine, threonine, and tryptophan. The human diet must supply these compounds, as they are crucial for protein synthesis.
Animal proteins often contain all essential amino acids, making them complete proteins. In contrast, plant proteins may lack one or more of the essential amino acids, rendering them incomplete. The concept of a "limiting amino acid" is used to describe a situation where a protein is deficient in one of the essential amino acids. Digestibility also plays a role in the nutritional value of a protein, with some plant proteins, like those found in wheat grains, being less completely digested and therefore less effective at providing essential amino acids.
Daily requirements for each essential amino acid vary, with infants and children needing greater amounts per kilogram of body weight compared to adults due to the demands of growth and protein synthesis. Additionally, while all living species use the same set of 20 amino acids to construct proteins, the exact number of amino acids considered essential may differ between organisms.