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Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location ...
The human genome, categorized by function of each gene product, given both as number of genes and as percentage of all genes. [7] Proteins may also be classified based on their cellular function. A widely used classification is PANTHER (protein analysis through evolutionary relationships) classification system. [7]
Proteins are essential nutrients for the human body. [1] They are one of the building blocks of body tissue and can also serve as a fuel source . As a fuel, proteins provide as much energy density as carbohydrates : 17 kJ (4 kcal ) per gram; in contrast, lipids provide 37 kJ (9 kcal) per gram.
To understand the functions of proteins at a molecular level, it is often necessary to determine their three-dimensional structure. This is the topic of the scientific field of structural biology , which employs techniques such as X-ray crystallography , NMR spectroscopy , cryo-electron microscopy (cryo-EM) and dual polarisation interferometry ...
Membrane proteins perform a variety of functions vital to the survival of organisms: [2] Membrane receptor proteins relay signals between the cell's internal and external environments. Transport proteins move molecules and ions across the membrane.
The tertiary structure is the proteins overall 3D structure which is made of different secondary structures folding together. In the tertiary structure, key protein features e.g. the active site, are folded and formed enabling the protein to function. Finally, some proteins may adopt a complex quaternary structure. Most proteins are made of a ...
Globulins make up 38% of blood proteins and transport ions, hormones, and lipids assisting in immune function. Fibrinogen comprises 7% of blood proteins; conversion of fibrinogen to insoluble fibrin is essential for blood clotting. The remainder of the plasma proteins (1%) are regulatory proteins, such as enzymes, proenzymes, and hormones.
Eukaryotic cells contain organelles including mitochondria, which provide energy for cell functions; chloroplasts, which create sugars by photosynthesis, in plants; and ribosomes, which synthesise proteins. Cells were discovered by Robert Hooke in 1665, who named them after their resemblance to cells inhabited by Christian monks in a monastery.