Exhaustive Study Notes on Protein Structure, Folding, and Function

Vocabulary flashcards reviewing primary, secondary, tertiary, and quaternary protein structures, peptide bond chemistry, and protein stability concepts.

Peptide bond

An amide bond formed between the carboxyl group of one amino acid and the amine group of another amino acid.

Amino acid residues

The remaining portions of amino acids in a polypeptide chain after water is lost during peptide bond formation.

Primary structure

The linear sequence of amino acids in a protein chain, synthesized and read from the amino terminus to the carboxyl terminus.

Trans configuration

The predominant spatial arrangement of a peptide bond where R groups extend on opposite sides of the peptide backbone to minimize steric hindrance.

Cis configuration

A rare spatial arrangement occurring in approximately $0.001\%$ of protein structures where R groups are on the same side, requiring the enzyme isomerase to form.

Alpha helix

A helical secondary structure stabilized by hydrogen bonds between peptide bonds along the chain backbone, with R groups projecting outward.

Meta-stable alpha helix

An alpha helix with intermediate stability that allows a protein to rapidly switch between different conformational states.

Proline

A secondary amino acid with a rigid ring structure that introduces a kink into an alpha helix and is frequently positioned at helix ends or in beta turns.

Glycine

The smallest amino acid, whose minimal R group permits tight turns in polypeptide chains and close packing of alpha helices.

Beta sheet

A secondary structure held together by hydrogen bonds extending laterally between adjacent polypeptide chains, with R groups alternating up and down.

Anti-parallel beta sheet

A beta sheet configuration where adjacent polypeptide strands run in opposite N-terminus to C-terminus directions.

Parallel beta sheet

A beta sheet configuration where adjacent polypeptide strands run in the same N-terminus to C-terminus direction.

Beta turn

A tight secondary structure element stabilized by hydrogen bonding that reverses the direction of the polypeptide chain, often containing proline or glycine.

AlphaFold

An AI program that predicts tertiary protein structures from primary amino acid sequences using pattern recognition from thousands of known structures.

Motif

A small, recognizable assembly of secondary structure elements, such as the helix-turn-helix motif involved in DNA binding.

Tertiary structure

The overall three-dimensional folding structure formed by the assembly of secondary structure elements within a single polypeptide chain.

Chaperones

Specialized helper proteins that assist newly synthesized polypeptide chains in folding into their correct tertiary structure.

Domain

An independent folding unit within a single polypeptide chain that maintains its own distinct structure and function.

Quaternary structure

The three-dimensional protein structure resulting from the assembly of two or more separate polypeptide chains or subunits.

Collagen

A structural protein composed of a triple helix that acts as rebar in the extracellular matrix to provide high strength.

Native conformation

The naturally occurring, functional three-dimensional state of a protein.

Denaturation

The loss of a protein's native functional structure caused by the disruption of weak non-covalent interactions due to heat, pH changes, or solvents.

Zymogen

An inactive precursor form of an enzyme, such as a digestive protease, that requires cleavage or modification to become functionally active.