Introduction to Proteins and Amino Acids

Introduction to Proteins

• Proteins are large, complex molecules crucial for life.
• They are composed of amino acids linked together by peptide bonds.
• Diverse functions include structural support, catalysis, transport, and regulation.
• Structure and function are intricately linked.

Amino Acids

• Twenty standard amino acids make up all proteins.
• Each amino acid has a central carbon atom bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom (H), and a variable side chain (R group).
• The R group determines the specific properties of each amino acid.
• Some amino acids are essential, meaning they cannot be synthesized by the body and must be obtained from the diet.

Protein Structure

• Primary structure: The linear sequence of amino acids.
• Secondary structure: Localized folding patterns like alpha-helices and beta-sheets, stabilized by hydrogen bonds.
• Tertiary structure: The overall three-dimensional shape of the polypeptide chain, determined by interactions between R groups (e.g., hydrophobic interactions, hydrogen bonds, disulfide bonds).
• Quaternary structure: The arrangement of multiple polypeptide chains in a protein complex.

Protein Function

• Enzymes: Catalyze biochemical reactions.
• Structural proteins: Provide support and shape (e.g., collagen, keratin).
• Transport proteins: Bind and carry molecules throughout the body (e.g., hemoglobin, albumin).
• Regulatory proteins: Control gene expression and other cellular processes.
• Antibodies: Defend against pathogens.
• Hormones: Act as chemical messengers.
• Receptors: Bind to specific molecules to trigger cellular responses.

Protein Folding

• Proteins spontaneously fold into their unique three-dimensional shapes.
• This folding is crucial for their function.
• Chaperone proteins assist in the proper folding of other proteins.
• Misfolded proteins can lead to diseases like Alzheimer's and Parkinson's.

Protein Denaturation

• Denaturation is the loss of a protein's three-dimensional structure.
• This often occurs due to changes in pH, temperature, or exposure to chemicals.
• Denatured proteins typically lose their function.

Protein Synthesis

• Proteins are synthesized by ribosomes in cells.
• The process involves transcription of DNA into mRNA, transfer of mRNA to ribosomes, and translation of mRNA into a polypeptide chain.
• Specific genetic information determines the amino acid sequence in the protein.

Protein Digestion

• Proteins are broken down into smaller peptides and amino acids through hydrolysis during digestion.
• Digestive enzymes (proteases) catalyze these reactions.
• The absorbed amino acids are used by the body to synthesize new proteins or other nitrogen-containing molecules.

Protein Classification

• Fibrous proteins: Long, insoluble fibers crucial for structural support (e.g., collagen, keratin).
• Globular proteins: Compact, soluble proteins involved in various functions (e.g., enzymes, antibodies).

Importance of Protein in Nutrition

• Essential for building and repairing tissues.
• Critical for various biological processes.
• A balanced protein intake is essential for maintaining health.
• Dietary protein sources include meat, poultry, fish, eggs, dairy, legumes, and nuts.

Protein Quality

• Protein quality refers to the digestibility and amino acid content.
• Complete proteins provide all essential amino acids.
• Incomplete proteins lack one or more essential amino acids.
• Combining incomplete proteins can provide all essential amino acids.