Alpha helices in coiled coils Alpha helices are named after alpha keratin, a fibrous protein consisting of two alpha helices twisted around each other in a coiled-coil (see Coiled coil). In leucine zipper proteins (such as Gcn4), the ends of the two alpha helices bind to two opposite major grooves of DNA.

Alpha Helix structure of DNA is more stable than Beta pleated Sheet structure. It is stabilized by the regular formation of hydrogen bonds parallel to the axis of the helix; they are formed between the amino and carbonyl groups of every fourth peptide bond.

No change was observed upon heating a beta-sheet sample, perhaps due to kinetic effects and the different heating rate used in the experiments. These results are consistent with beta-sheet approximately 260 J/mol more stable than alpha-helix in solid-state PLA.

Beta-sheets consist of extended polypeptide strands (beta-strands) connected by a network of hydrogen bonds and occur widely in proteins. The importance of beta-sheet interactions in biological processes makes them potential targets for intervention in diseases such as AIDS, cancer, and Alzheimer’s disease.

Antiparallel ß sheets are slightly more stable than parallel ß sheets because the hydrogen bonding pattern is more optimal.

β-Sheets are formed when several β-strands self-assemble, and are stabilized by interstrand hydrogen bonding, leading to the formation of extended amphipathic sheets in which hydrophobic side-chains point in one direction and polar side-chains in the other (Fig. 3.1D,E).

Amino acid propensities Large aromatic residues (tyrosine, phenylalanine, tryptophan) and β-branched amino acids (threonine, valine, isoleucine) are favored to be found in β-strands in the middle of β-sheets.

Gratifyingly, the turn propensities of amino acids at different positions of various protein β-turn types obtained through statistical analysis by directed evolution and phage-display correlate well with work on model peptides in showing glycine, proline, asparagine, and aspartic acid to be the most common β-turn- …

Primary structure is the amino acid sequence. Secondary structure is local interactions between stretches of a polypeptide chain and includes α-helix and β-pleated sheet structures. Tertiary structure is the overall the three-dimension folding driven largely by interactions between R groups.

Protein tertiary structure. Protein tertiary structures are the result of weak interactions. For example, amide hydrogen atoms can form H‐bonds with nearby carbonyl oxygens; an alpha helix or beta sheet can zip up, prompted by these small local structures.

The tertiary structure of a protein refers to the overall three-dimensional arrangement of its polypeptide chain in space. It is generally stabilized by outside polar hydrophilic hydrogen and ionic bond interactions, and internal hydrophobic interactions between nonpolar amino acid side chains (Fig.

_____ Which is a property of tertiary structure and quaternary structure? a) Both structures are stabilized by numerous covalent hydrophobic and hydrophilic interactions.

Quaternary structure is an important protein attribute that is closely related to its function. Proteins with quaternary structure are called oligomeric proteins. Oligomeric proteins are involved in various biological processes, such as metabolism, signal transduction, and chromosome replication.

Quaternary structure is held together by noncovalent bonds between complementary surface hydrophobic and hydrophilic regions on the polypeptide subunits.

Linus Pauling. 7. Fibrous proteins, such as the keratin of your hair, contain almost exclusively primary and secondary structure, but no tertiary or quaternary structure. A special and important fibrous protein is collagen, which has three polypeptide chains intertwined in a helical structure.

The quaternary structure of collagen consists of three left-handed helices twisted into a right-handed coil. Molecular model studies show that this sequence works the best for the triple helix structure. Glycine is needed because it is small and is the only amino acid which can fit in the interior of the triple helix.

In nature, some proteins are formed from several polypeptides, also known as subunits, and the interaction of these subunits forms the quaternary structure. For example, insulin (a globular protein) has a combination of hydrogen bonds and disulfide bonds that cause it to be mostly clumped into a ball shape.

All 16 types of collagen contain a repeating Gly-Pro-X sequence and fold into a characteristic triple-helical structure. The various collagens are distinguished by the ability of their helical and nonhelical regions to associate into fibrils, to form sheets, or to cross-link different collagen types.

Vascular and Arthrochalasia Type Collagen I is found in virtually all extracellular matrices, including bone, skin, and tendons while collagen III also is an important component of blood vessels and hollow organs (1). Mutations in collagen type III underlie the vascular type of EDS (EDS type IV).

A collagen molecule consists of three polypeptide chains arranged in a parallel triple-helix. The individual polypeptide chains are called alpha-chains, and although each is helical they only have this conformation when associated with two other alpha chains; they should not be confused with alpha-helices.

Hydroxyproline and proline play key roles for collagen stability. They permit the sharp twisting of the collagen helix. In the canonical collagen Xaa-Yaa-Gly triad (where Xaa and Yaa are any amino acid), a proline occupying the Yaa position is hydroxylated to give a Xaa-Hyp-Gly sequence.

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