(25) B1.2 Proteins [IB Biology SL/HL]

Overview of Proteins

  • Definition: Proteins are long chains of monomers called amino acids.

  • Amino Acids: There are 20 different types, each with unique structures determined by their R groups.

Amino Acid Structure

  • General Structure:

    • Central carbon atom

    • Carboxyl Group: A double-bonded oxygen and a hydroxy group.

    • Amine Group: Consists of a nitrogen atom and two hydrogen atoms.

    • Hydrogen Atom: Attached to the central carbon.

    • Functional Group (R group): Varies among different amino acids.

  • 3D Structure: Amino acids exist in three-dimensional configurations, and they can be represented in various orientations (e.g., mirror images).

Formation of Polypeptides

  • Connecting Amino Acids:

    • Connecting two amino acids forms a dipeptide (di- meaning two).

    • Multiple amino acids bond to form a polypeptide.

  • Condensation Reactions:

    • Involves the removal of water to bond amino acids together.

  • Peptide Bond:

    • A special bond formed between two amino acids during this process.

    • This bond is crucial for the formation of dipeptides and polypeptides.

Essential and Non-Essential Amino Acids

  • Production:

    • Humans can manufacture only 9 out of the 20 amino acids necessary for protein synthesis.

    • The remaining 11 must be obtained through diet and are termed essential amino acids.

  • Dietary Implications:

    • It's important to include a variety of protein sources to ensure a balanced intake of all essential amino acids.

    • Animal proteins (e.g., eggs) typically contain all essential amino acids, while some plant proteins may lack certain ones.

Protein Synthesis and Structure

  • Role of DNA and RNA:

    • DNA encodes the information for assembling polypeptides.

    • RNA acts as a messenger for this genetic code, facilitating protein synthesis.

  • Proteome:

    • The complete set of proteins that can be made by an organism, reflecting the unique arrangement of amino acids coded by genes.

  • Examples of Proteins: Insulin and myoglobin demonstrate how different sequences of amino acids result in proteins with distinct structures and functions.

Distinction Between Polypeptide and Protein

  • A polypeptide becomes a protein when it folds into a specific three-dimensional shape, essential for its function.

  • The function of a protein depends on its shape, which is determined by various bonds and interactions.

Denaturation of Proteins

  • Definition: A permanent alteration in the structure of a protein, affecting its functionality.

  • Causes of Denaturation:

    • Temperature: Increased temperature can enhance reaction rates until reaching a denaturation point where the protein unravels.

    • pH Levels: Optimal pH for each protein; deviations can disrupt interactions that maintain the protein's shape, leading to decreased functionality.

  • Examples of Denaturation: Blood clotting involves proteins that can become insoluble, which change from their normal functional state due to denaturation.

Conclusion

  • Form and Function: A protein's form is crucial to its function; any change in the protein's shape through denaturation or other means directly impacts its ability to perform biological tasks.