1989 Jul 109(1):93-100.Chapter 2: Protein Structure 2.1 Amino Acid Structure and Properties 2.2 Peptide Bond Formation and Primary Protein Structure 2.3 Secondary Protein Structure 2.4 Supersecondary Structure and Protein MotifsĢ.5 Tertiary and Quaternary Protein Structure 2.6 Protein Folding, Denaturation and Hydrolysis 2.7 References Acidification of the lysosome-like vacuole and the vacuolar H+-ATPase are deficient in two yeast mutants that fail to sort vacuolar proteins. Rothman JH, Yamashiro CT, Raymond CK, Kane PM, Stevens TH. Vesicle fusion following receptor-mediated endocytosis requires a protein active in Golgi transport. 1980 Feb 77(2):780-4.ĭiaz R, Mayorga LS, Weidman PJ, Rothman JE, Stahl PD. Coated vesicles transport newly synthesized membrane glycoproteins from endoplasmic reticulum to plasma membrane in two successive stages. Biological surface properties in extracellular vesicles and their effect on cargo proteins. Santucci L, Bruschi M, Del Zotto G, Antonini F, Ghiggeri GM, Panfoli I, Candiano G. Determination of base and backbone contributions to the thermodynamics of premelting and melting transitions in B DNA. These macromolecules continue to elongate until they eventually precipitate and distort the red blood cell's plasma membrane into the classic sickle shape seen in a sickle cell crisis.Ĭopyright © 2023, StatPearls Publishing LLC. These altered hemoglobin molecules then form polymers that manifest as long, inflexible rods. An example of the clinical significance is in sickle cell anemia, whereby the hemoglobin protein made possesses amino acids that are insoluble in an aqueous environment, driving the defective hemoglobin to aggregate to hide newly formed hydrophobic residues and achieve thermodynamic favorability. It is important to note that the term subunit is interchangeable with protomer. Therefore it is appropriate to say that quaternary structure is the three-dimensional arrangement of two or more polypeptides in a protein, each of which folds independently of the other. An example of this is hemoglobin and how its tetrameric structure forms when two alpha and two beta subunits are held together by chemical interactions. This level is when complexes form from multiple polypeptide chains called subunits. The fourth and final level of protein structure is called the quarternary structure. The energy that these interactions can produce ranges from 0.1 to 3 kilocalories per mole. This thermodynamic stability is further driven by a variety of chemical interactions to include hydrogen bonds, Vanderwall forces, and ionic bonding (the term ionic bonding includes electrostatic interactions and salt bridges). The polypeptide chain sequesters hydrophobic residues and exposes those that are hydrophilic this is all to achieve thermodynamic stability. It consists of the three-dimensional shape that will form when the polypeptide chain "backbone" interacts with an aqueous environment, which immediately begins to form when a newly synthesized polypeptide chain exits the terminal end of the ribosomal subunit complex. The third level of protein structure is the tertiary structure. As previously stated, hydrogen bonds stabilize all of these shapes. These shapes include alpha helix, beta-pleated sheet, and beta-turn. The second level of protein structure is the secondary structure, and it consists of the various shapes form via hydrogen bonding. This structure also has the name of the protein backbone. These linkages have designated carbon atom positions of alpha, beta, and gamma, which correspond to specific positions relative to the peptide linkage. All of the residues connect via peptide bonds. It is composed of the linear order of amino acid residues. The first level is the primary structure because it is the most basic level of protein structure. Proteins can be further defined by their four structural levels: primary, secondary, tertiary, and quaternary. Proteins serve as structural support, biochemical catalysts, hormones, enzymes, building blocks, and initiators of cellular death. Proteins are biopolymeric structures composed of amino acids, of which there are 20 commons found in biological chemistry.
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