What is protein made of
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Understanding the Composition of Proteins
Proteins: Polymers of Amino Acids
Proteins are essential macromolecules found in all living cells, composed of long chains of amino acids. These amino acids are linked together by peptide bonds, forming polymers that can be represented in various structural forms: primary, secondary, tertiary, and quaternary structures Watford2018Sforza2015Labuda2019. The primary structure, which is the sequence of amino acids, is of particular interest from a nutritional perspective .
The Building Blocks: Amino Acids
Proteins are made up of 20 different amino acids, which are encoded by DNA. These amino acids can be categorized into essential and non-essential types. Essential amino acids, such as leucine, valine, and lysine, cannot be synthesized by the human body and must be obtained through diet. Non-essential amino acids, like glutamate and serine, can be synthesized by the body Watford2018Séquaris1980Agarwal2017. Additionally, some amino acids are considered conditionally indispensable, meaning they are required in higher amounts during specific physiological or pathological conditions .
Nutritional and Functional Roles
Proteins play a variety of roles in the body, including structural support (e.g., collagen in connective tissues), mechanical functions (e.g., muscle proteins like myosin and actin), biochemical activities (e.g., enzymes), and cell signaling (e.g., hormones) Labuda2019Séquaris1980Bonifacino2000. They are also crucial for maintaining fluid and electrolyte balance, energy production, and the transport of nutrients and oxygen .
Protein Sources and Quality
Dietary proteins come from various sources, including animal products (meat, eggs, milk) and plant-based foods (soy, pulses). Animal proteins generally contain all essential amino acids, making them high-quality proteins. In contrast, plant proteins often lack one or more essential amino acids, although they can still be valuable when consumed in combination with other protein sources Sforza2015Lusas1995Agarwal2017.
Protein Metabolism and Turnover
Once consumed, proteins are digested into small peptides and free amino acids, which are then absorbed and used for protein synthesis within cells. The body continuously breaks down and synthesizes proteins, a process known as protein turnover. For individuals in nitrogen balance, the amount of protein degraded daily is equal to the amount consumed, with nitrogen being excreted as urea and ammonia .
Structural Complexity
The structure of proteins is complex and can be described at multiple levels. The primary structure is the amino acid sequence, while the secondary structure includes spatial arrangements like alpha-helices and beta-sheets. The tertiary structure refers to the three-dimensional shape of the protein, and the quaternary structure involves the arrangement of multiple protein subunits . This structural complexity allows proteins to perform a wide range of functions in the body Wrinch1937Kadakeri2020.
Conclusion
Proteins are vital macromolecules composed of amino acids, playing diverse roles in the body from structural support to biochemical activities. Understanding their composition, sources, and functions is crucial for appreciating their importance in nutrition and overall health.
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Proteins: Chemistry, Characterization, and Quality
Food proteins are essential for maintaining nutritional value and providing structure in various food commodities, and analytical methods are crucial for determining their concentration, type, molecular structure, and functional properties.
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Chapter 3 – Proteins
Proteins are complex polymers made up of amino acids, with primary structure indicating the order and sequence of AAs, secondary structure indicating the spatial distribution of AAs, and tertiary structure indicating the tridimensional shape that the protein adopts.
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