Protein

protein molecule size comparison

enzyme

Proteins are large molecules built from peptides: chains of amino acids held together with peptide bonds. A polypeptide is a single linear chain of two or more amino acids. Protein molecules consist of one or more polypeptides put together typically in a biologically functional way. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond. There can also be tripeptides, tetrapeptides, pentapeptides, etc.

Proteins are used to make new tissue and cells, as enzymes (catalysts that accelerate chemical reactions in the body), hormones (chemical messengers), or antibodies (immunological agents).

They can be found in animals, plants, fungi, and bacteria. There are four factors that determine what a protein will do. The first is the order of the amino acids. There are 20 amino acids, and they are all a bit different. The second is the twists in the chain. The third is how the entire thing is folded up. The fourth is whether it’s working with other proteins.

Animals eat proteins and break them down into amino acids in order to recombine them into other things needed, including other proteins. They have certain amino acids they are not able to create this way, and must get from their food, called ‘essential amino acids,’ and different animals have different amino acids they are not able to create.

Animal foods such as meat, dairy, eggs, poultry, and fish are ‘complete proteins’ because they contain all essential amino acids for humans. Plants are not complete proteins, but eating a mixture of plants, such as grains plus legumes (corn tortilla and beans, bread and peanut butter, rice and tofu) can provide all essential amino acids.

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