Sekundäärirakenteen

Sekundäärirakenteen, often translated as secondary structure, refers to the three-dimensional folding patterns of macromolecules, particularly proteins and nucleic acids. In the context of proteins, secondary structure describes the local arrangements of the polypeptide chain, primarily stabilized by hydrogen bonds between atoms of the peptide backbone. The most common secondary structures are the alpha-helix (α-helix) and the beta-sheet (β-sheet). An α-helix is a helical conformation where the polypeptide chain coils like a spring, with hydrogen bonds forming between the carbonyl oxygen of one amino acid residue and the amide hydrogen of another located four residues further along the chain. A β-sheet, on the other hand, is formed by strands of polypeptide chain lying side-by-side, with hydrogen bonds connecting the peptide backbone atoms of adjacent strands, creating a pleated or folded sheet-like structure. Other less common secondary structures include beta-turns and loops.

For nucleic acids like RNA and DNA, secondary structure refers to the formation of base pairs that create local helical regions. In RNA, this commonly includes stem-loops (also known as hairpin loops) and internal loops. A stem is formed by a region of base pairing, typically A-U and G-C, creating a double-stranded helix, while the loop is an unpaired region of nucleotides. In DNA, the dominant secondary structure is the double helix, formed by two complementary strands held together by hydrogen bonds between base pairs. The understanding of secondary structure is crucial as it contributes to the overall tertiary structure and ultimately the function of these biomolecules.