2.3 Proteins

proteins

molecule containing one or more polypeptides folded into specific 3D shapes. E.g. enzymes, receptor, structural and signalling

amino acid

organic molecule with carboxyl group, amino group and side chain (R) - monomers of polypeptides

why do amino acids show both acidic and basic qualities?

Carboxyl group donates protons, while amino group accepts protons.

peptides

Short chains of amino acids linked by peptide bonds, forming the building blocks of proteins.

polypeptides

A polymer of many amino acids linked together by peptide bonds.

peptide bond

The covalent bond between the carboxyl group on one amino acid and the amino group on another, formed by a condensation reaction

what are the names of the beginning and end of polypeptides

Amino group of 1st amino acid = N terminus

carboxyl of last amino acid C terminus

primary structure

The unique sequence of amino acids in a polypeptide chain linked by peptide bonds, determining its overall structure and function.

secondary structure

The regular arrangements of amino acids in localized regions of a polypeptide, typically forming alpha helices and beta sheets due to hydrogen bonding.

tertiary structure

The overall 3D of a polypeptide, determined by interactions among various side chains and influences functionality

interactions between R groups in tertiary structures

• covalent disulfide bridges between specific cysteine side chains = holds folded polypeptide in place

• hydrogen bonds between side chains = stabilise protein folds

• hydrophobic side chains combine in protein interior away from water causing polypeptide to fold = stabilised by van der Waals forces

• ionic bonds between positive and negatively charged side chains = salt bridges between amino acids

denaturation

The process by which a protein loses its native structure, often due to external stressors like heat, pH changes, or chemical exposure, leading to a loss of functionality.

If a protein is gently heated to break hydrogen bonds, what levels of structure will be unaffectedand why?

Primary structure remains unaffected because it is held together by peptide bonds, which are not disrupted by heat.

quaternary structure

is the highest level of protein organization, involving the assembly of multiple polypeptide chains into a functional complex, stabilized by various interactions such as hydrogen bonds, ionic bonds, and hydrophobic interactions.

what 2 factors affect proteins binding to other molecules

shape and chemistry (exposed R groups permit interactions with other substances

molecular chaperones

proteins that assist in proper folding of other proteins to prevent aggregation and misfolding. Binds to other proteins just made or recently denatured as this is when binding with wrong substances is most likely

disulphide bridge

A strong covalent bond formed when the sulfur of one cysteine monomer bonds to the sulfur of another cysteine monomer, contributing to proteins stability and tertiary structure.