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Answer:
C.The β‑pleated sheet is held together by hydrogen bonds between adjacent segments.
Explanation:
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The most common secondary structures are α-helix and β-sheets. The structures are defined by regular hydrogen bonds formed between the N-H and C=O groups of the amino acids that form the chain. These structures form in segments of the protein as an intermediate before it folds into the 3D tertiary structure.
α helix
It is a cylindrical structure that comprehends a helical backbone, while the side chains extend outward in a helical distribution. The α-helix stabilizes through hydrogen bonds between the amines and carbonyls groups of the backbone. Each carbonyl group forms a hydrogen bond with the amine group four residues later in the main chain. Thus, except for the amino acids near the end of the α-helix, all the carbonyls and amines groups in the main chain are linked by hydrogen bonds. Each residue corresponds to a translation of 1,5Ǻ and a turn of 100º this equals 3,6 residues per turn.
From the observer point of view, if the rotation of the helix is clockwise or right-handed, it's called dextrorotation and if the rotation is counterclockwise or left-handed it's called levorotation. Dexorotation or dextrogyre is the most common rotation of α-helixes in proteins. Levorotation or levogyre is very rare but can be found in proteins with a large content of achiral glycine.
β-sheets (β-pleated sheets)
This structure consists of at least two β-strands (polypeptide chains), the strands conform a backbone of three to ten amino acids in an extended formation that connects laterally with hydrogen bonds. The distance between adjacent amino acids in a β-strand is approximately 3,5Ǻ in contrast to the 1,5Ǻ distance of an α helix. The chains that form a β-sheet have directionality conferred by their N-terminus and C-terminus. Adjacent β-strands can form hydrogen bonds in antiparallel, parallel or mixed arrangements. In the antiparallel arrangement, the adjacent strands are said to have opposite directions (N-C vs C-N) this allows the bonds to be established between the amines and carbonyls groups of each amino acid with the carbonyls and amines of the adjacent amino acid. This way the bonds between carbonyls and amines are planar, which allows strong interstrand stability.
In the parallel arrangement, the adjacent strands have the same direction (N-C vs N-C). In this type of arrangement, each amine forms a hydrogen bond with the carbonyl of the adjacent amino acid, but its carbonyl group forms a hydrogen bond with the amine group of the amino acid two residues later.
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Correct statements related to the secondary structure of proteins are:
C. The β-folded sheet joined by hydrogen bonds between adjacent segments.
Further explanation
Protein structure includes primary structure, secondary structure, tertiary structure, and quaternary structure. Every protein, especially polypeptide, is a polymer which is a sequence formed from various L-α-amino acids (this sequence is also referred to as a residue). The three-dimensional structure of proteins is very necessary to understand the function of proteins at the molecular level.
Proteins are classified based on their physical size as nanoparticles. A protein can undergo reversible structural changes in carrying out its biological functions. Alternative structures of the same protein are called conformations.
Primary Protein Structure
This structure refers to the linear amino acid sequence of the polypeptide chain. This structure occurs because of the bond between the peptide and the convalescent, which occurs when the process of protein biosynthesis or commonly referred to as the translation process.
Secondary Protein Structure
This structure refers to regular sub-structure. The two main types of secondary structures are alpha helices and beta sheets. The secondary structure is determined by the hydrogen-bonding pattern between the main chain peptide groups.
Tertiary Protein Structure
Tertiary structure refers to the three-dimensional structure of a single protein molecule. Alpha helices and beta sheets are turned into spheres. The fold is controlled by hydrophobic interactions, but the structure can be stabilized only if the parts of the protein are locked into place by specific tertiary interactions.
Quaternary Protein Structure
This structure is a three-dimensional structure of several protein subunits that are bound together. In this context, quarterly structures are stabilized by the same non-covalent interactions and disulfide bonds as tertiary structures.
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Details
Class: College
Subject: Biology
Keyword: Secondary Protein Structure
