Protein Structure and Function
This section provides an in-depth look at protein structure and function, which is a crucial component of biological molecules A level AQA curriculum. It covers the different levels of protein structure and introduces important concepts for AQA A Level Biology Biological Molecules flashcards.
The guide begins by distinguishing between two types of proteins: globular and fibrous. Globular proteins are described as soluble proteins with a specific 3D shape, with examples including enzymes, hormones, antibodies, and hemoglobin. Fibrous proteins are characterized as strong, insoluble, and inflexible materials, with collagen and keratin given as examples.
The building blocks of proteins, amino acids, are introduced. The guide provides a detailed description of the amino acid structure, including the central carbon atom, carboxyl group (COOH), amine group (NH2), hydrogen, and the variable R group. It explains that different amino acids are distinguished by their unique R groups.
The formation of peptide bonds through condensation reactions between amino acids is explained, leading to the creation of dipeptides and eventually polypeptides.
The four levels of protein structure are defined:
- Primary structure: The sequence of amino acids in a polypeptide chain, held together by peptide bonds.
- Secondary structure: The coiling of the primary structure to form a helix, stabilized by hydrogen bonds.
- Tertiary structure: Further folding of the secondary structure to create the final 3D shape, held together by various bonds including hydrogen, ionic, and disulfide bonds.
- Quaternary structure: Proteins composed of more than one polypeptide chain.
Examples of proteins with quaternary structure are provided, including collagen (3 chains), antibodies (3 chains), and hemoglobin (4 chains).
The structure of collagen is described in detail, emphasizing its role as a strong material used in tendons, ligaments, and connective tissues. Its primary structure is noted to be mainly composed of glycine, the simplest amino acid, which allows for tight coiling in the secondary and tertiary structures.
The section concludes with a description of the biuret test for proteins, which results in a purple color change.
Vocabulary: Peptide bond - A covalent bond formed between the carboxyl group of one amino acid and the amino group of another, resulting in the release of a water molecule.
Example: Hemoglobin, a protein with quaternary structure, is composed of four polypeptide chains.
Definition: Tertiary structure - The final three-dimensional shape of a protein, resulting from further folding of the secondary structure and stabilized by various types of bonds.
Highlight: The presence of glycine in collagen's primary structure allows for tight coiling, contributing to its strength as a structural protein.
Quote: "Structure of collagen? strong material, used to build tendons/ligaments/connective tissues"
