Proteins and Their Functions

Proteins

• Proteins are versatile molecules in the body with numerous functions.
• The term "protein" comes from the Greek word "Proteus," meaning "primary."
• Proteins are polymers of amino acids, composed of 20 different amino acids in varying numbers and sequences that are covalently linked.
• The general formula for proteins is CHON.

Functions of Proteins

• Repair and maintain body tissues.
• Important in blood coagulation and immunologic function.
• Transport metabolic substances.
• Maintain osmotic pressure and blood pH.
• Act as biocatalysts.

Amino Acids

• Amino acids are large molecules (macromolecules) and the fundamental building blocks of proteins.
• There are 20 different amino acids, with 8 essential amino acids that cannot be produced by the body and must be supplied through diet.
• The essential amino acids are:
  • Valine
  • Leucine
  • Isoleucine
  • Phenylalanine
  • Tryptophan
  • Methionine
  • Threonine
  • Lysine

Characteristics of Amino Acids

• Amino acids have an electric charge that depends on the pH of the solution and the type of R group.
• In basic solutions, amino acids have a negative charge, while in acid solutions, they have a positive charge.
• This charge affects how proteins move in an electric field, allowing them to be separated.

Protein Structure

• The structure of a protein dictates its function.
• The primary structure of a protein refers to the number and sequence of amino acids, which is determined by the DNA coding.
• The primary structure determines the identity of proteins, molecular structure, binding capacity, and recognition capacity.
• The secondary structure of a protein refers to the coiling and folding of the protein chain, determined by the interaction of adjacent amino acids.
• The tertiary structure of a protein refers to the 3-dimensional shape governed by various covalent and non-covalent bonds.
• The quarternary structure of a protein refers to the combination of two or more polypeptide chains that associate closely together.

Classes of Proteins

• Enzymes: biochemical catalysts that accelerate or decelerate biochemical reactions.
• Structural proteins: provide structural support for the body, a tissue, or a cell, and are usually long, fibrous molecules.
• Contractile proteins: involve in the contraction and relaxation of muscles, allowing movement of individuals, and are usually long, fibrous materials.
• Antibodies: proteins produced by certain immune cells that effectively neutralize foreign material.