Lecture Notes on Macronutrients: Proteins

Overview of Proteins

• Proteins are essential macronutrients found in the body, made up of thousands of proteins.
• North Americans often consume more protein than necessary.
• Proteins serve various functions including structural roles, regulation, maintenance of body functions, and energy supply (4 calories per gram).
• Proteins provide essential nitrogen in the form of amino acids.

Amino Acids

• Proteins are made from 20 different amino acids.
  • Essential Amino Acids (9): Cannot be synthesized by the body, must be obtained from the diet.
  • Non-Essential Amino Acids (11): Can be synthesized by the body.
• All amino acids contain carbon, hydrogen, oxygen, and nitrogen.
• R Group: Unique side chain that differentiates amino acids.
  • Determines differences among amino acids.

Branched Chain Amino Acids (BCAAs)

• Essential amino acids with a branched R group structure.
  • Examples: Leucine, Isoleucine, Valine.
• Important as muscles can use carbon skeletons for fuel.
• Whey protein is a rich source of BCAAs.

Protein Quality and Synthesis

• Limiting Amino Acid: The essential amino acid in the lowest concentration relative to needs.
• Conditionally Essential Amino Acids: Normally non-essential but become essential under certain conditions (e.g., rapid growth, disease).
  • Example: Tyrosine becomes essential in PKU due to enzyme deficiency affecting phenylalanine metabolism.

Protein Structure

• Peptide Bonds: Chemical bonds linking amino acids.
  • Dipeptides (2 amino acids), Tripeptides (3), Oligopeptides (4-9), Polypeptides (10+).
• Proteins are synthesized from DNA instructions.
  • Transcription: DNA to mRNA in the nucleus.
  • Translation: mRNA to protein in the ribosome with the help of tRNA.

Protein Function and Denaturation

• Protein structure determines function.
• Denaturation: Alteration of protein structure due to heat, enzymes, acids, etc.
  • Causes loss of biological activity, e.g., in cooking and digestion.

Disease Related to Protein Structure

• Sickle Cell Anemia: Malformation due to incorrect amino acid sequence in hemoglobin.
  • Glutamic acid replaced by valine.
  • Results in blocking of blood flow and reduced oxygen, potentially leading to complications.

Conclusion

• Understanding protein structure, function, and metabolism is crucial for nutritional science and health.