Proteins have four recognized levels of structure, which can be used to sort images of proteins according to their structural complexity:
- Primary structure : This is the linear sequence of amino acids in a polypeptide chain, connected by peptide bonds. It is the simplest level of structure and does not show folding or spatial arrangement
- Secondary structure : This level involves local spatial arrangements of the polypeptide backbone, mainly alpha-helices and beta-sheets, stabilized by hydrogen bonds between backbone atoms near each other in the chain
- Tertiary structure : This is the overall three-dimensional folding of a single polypeptide chain, including interactions between side chains (R groups) that stabilize the folded shape, such as ionic bonds, hydrogen bonds, disulfide linkages, and hydrophobic interactions
- Quaternary structure : This level applies to proteins composed of multiple polypeptide subunits. It describes how these subunits assemble and interact to form a biologically active complex
How to sort protein images by structure level
- Primary structure images show only a sequence of amino acids without folding or shape.
- Secondary structure images display local folded elements like alpha-helices (spirals) or beta-sheets (arrows or pleated sheets).
- Tertiary structure images depict the full 3D shape of a single polypeptide chain, often shown as ribbons or space-filling models.
- Quaternary structure images illustrate multiple polypeptide chains interacting, often with different colors for each subunit.
Thus, to sort images into bins:
- Put images showing only amino acid sequences into the Primary structure bin.
- Place images showing alpha-helices and beta-sheets into the Secondary structure bin.
- Assign images showing the entire folded 3D shape of one polypeptide to the Tertiary structure bin.
- Sort images depicting multiple interacting polypeptide chains into the Quaternary structure bin
This classification reflects the hierarchical organization of protein structure from simplest (primary) to most complex (quaternary)
