Protein Structures

Protein Structures

• Primary Structure

  • Refers to the arrangement of amino acids in a polypeptide chain.

• Secondary Structure

  • Involves the folding or coiling of polypeptide chains into stable structures.

  • Stabilized by hydrogen bonds between amino (–NH) groups of one amino acid and carboxyl (–COOH) groups of another.

  • Main Types:

    • Alpha Helix:

      • A coiled structure resembling a wave.

    • Beta Pleated Sheet:

      • Folded structure creating a sheet-like formation.

• Tertiary Structure

  • Refers to the 3D shape of a protein formed by the interaction of secondary structures.

  • Example: Hemoglobin, consisting of two alpha chains and two beta chains, facilitates oxygen transport.

Protein Synthesis

• Protein Formation

  • Occurs through protein synthesis, which is divided into two main stages:

    • Transcription:

      • The process of creating mRNA from a DNA template.

      • Key components include the coding strand, template strand, and RNA polymerase.

    • Translation:

      • The synthesis of proteins based on the sequence of mRNA.

• Details of Transcription

  • Initiation sequenced by RNA polymerase binding to a promoter on the template strand.

  • Elongation phase involves adding nucleotides to form a complete mRNA strand.

  • Final step characterized by a stop codon.

• RNA Processing

  • Involves capping, addition of a poly-A tail, and splicing.

  • Capping: A modified guanine added to the 5' end of the mRNA for stability.

  • Poly-A Tail Addition: A sequence of adenine nucleotides added to the 3' end for stability.

  • Splicing: Removes introns (non-coding regions) from pre-mRNA, preserving exons for protein synthesis.

Functions of Proteins

• Proteins serve various essential functions in the body, including:

  • Enzymes: Catalyze biochemical reactions (e.g., digestive enzymes).

  • Transport Proteins: Such as hemoglobin, which transports oxygen and carbon dioxide.

  • Structural Proteins: Provide support (e.g., keratin in hair and nails).

  • Hormones: Like insulin, regulate physiological processes (e.g., blood sugar levels).

  • Contractile Proteins: Enable muscle movement (e.g., actin and myosin).

  • Protective Proteins: Involved in immune responses (e.g., antibodies).

Nutritional Importance of Proteins

• Dietary Proteins

  • Essential for providing amino acids necessary for protein synthesis.

  • Unlike carbohydrates, excess proteins cannot be stored in the body; they are excreted as urea.

  • Need to consume a balanced variety of proteins for a complete set of amino acids.

• Amino Acid Metabolism

  • After digestion, proteins are broken down into amino acids that are absorbed and utilized by the body to form new proteins.