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The mechanical properties of proteins are highly diverse and are often central to their biological function, as in the case of proteins like keratin and collagen. [110] For instance, the ability of muscle tissue to continually expand and contract is directly tied to the elastic properties of their underlying protein makeup.
Protein structures range in size from tens to several thousand amino acids. [2] By physical size, proteins are classified as nanoparticles, between 1–100 nm. Very large protein complexes can be formed from protein subunits. For example, many thousands of actin molecules assemble into a microfilament.
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.
These properties influence protein structure and protein–protein interactions. The water-soluble proteins tend to have their hydrophobic residues ( Leu , Ile , Val , Phe , and Trp ) buried in the middle of the protein, whereas hydrophilic side chains are exposed to the aqueous solvent.
The simple summary is that DNA makes RNA, and then RNA makes proteins. DNA, RNA, and proteins all consist of a repeating structure of related building blocks (nucleotides in the case of DNA and RNA, amino acids in the case of proteins). In general, they are all unbranched polymers, and so can be represented in the form of a string.
The colloidal protein hypothesis stated that proteins were colloidal assemblies of smaller molecules. This hypothesis was disproved in the 1920s by ultracentrifugation measurements by Theodor Svedberg that showed that proteins had a well-defined, reproducible molecular weight and by electrophoretic measurements by Arne Tiselius that indicated ...
These conformational changes, as a result of protein adsorption, can also denature the protein and change its native properties. Illustration of protein (green) ligand (red star) binding site alteration by the conformational change of the protein as a result of surface (blue) adsorption. Note how the ligand no longer fits into the binding site.
An alpha-helix with hydrogen bonds (yellow dots) The α-helix is the most abundant type of secondary structure in proteins. The α-helix has 3.6 amino acids per turn with an H-bond formed between every fourth residue; the average length is 10 amino acids (3 turns) or 10 Å but varies from 5 to 40 (1.5 to 11 turns).