Chemistry Labs

Grade 12

Protein structure and function

A protein is a sequence that folds into a shape; its surface and flexibility help determine what it can bind or catalyse.

1 Lower secondary2 Upper secondary3 Undergraduate4 Advanced5 Research

IntuitionIntuition: the central idea

A protein is a sequence that folds into a shape; its surface and flexibility help determine what it can bind or catalyse.

Explore the schematic model; it illustrates a concept rather than replacing experimental evidence.

SchoolSchool level: key concepts and a first application

Definition: Core concept

Primary structure is sequence; secondary structure includes α helices and β sheets stabilized mainly by backbone hydrogen bonds; tertiary structure is the full fold.

Examples at school level include enzymes that position substrates, antibodies that recognize antigens, transport proteins such as haemoglobin, and structural proteins such as keratin.

Key terms and meaning
TermInterpretation
Amino acidMonomer with an amino and a carboxyl group joined through a central carbon.
Peptide bondThe covalent link joining adjacent residues.
Fold / conformationThe three-dimensional arrangement adopted by a chain.

Example: Apply the idea

If a folded enzyme loses its native conformation, why may activity fall even though its amino-acid sequence is unchanged?

Solution

Unfolding changes the geometry and chemical environment of the active site and can expose hydrophobic residues, promoting aggregation.

UndergraduateUniversity level: quantitative description

ΔGfold=ΔH−TΔS\Delta G_{\mathrm{fold}}=\Delta H-T\Delta S

The equilibrium folding constant can be written as Kf=[folded]/[unfolded]K_f=[folded]/[unfolded]; small free-energy differences often determine whether a protein is stable enough for a given cellular role.

References