Amino Acids and Proteins Quiz

Amino Acids and Proteins

• Amino acids are organic compounds containing a carboxylic acid group, hydrogen, an amino group, and a distinctive side group.
• Approximately 300 amino acids exist naturally, but only 20 are common components of proteins coded by DNA; these are called proteinogenic amino acids.
• Proteinogenic amino acids are classified as essential or nonessential based on their nutritional availability to vertebrates.
• Nonessential amino acids are those synthesized by vertebrates.
• Essential amino acids are those that vertebrates cannot synthesize and must obtain from plant or lower animal consumption.

Amino Acid Classification Based on Polarity

• Proteinogenic amino acids can also be categorized by the polarity of their R-groups:
  • Uncharged nonpolar amino acids
  • Uncharged polar amino acids
  • Positively charged amino acids
  • Negatively charged amino acids

Peptide Bond Formation

• Polypeptides are linear polymers of amino acids linked by peptide bonds.
• Peptide bonds are amide linkages between the carboxyl group of one amino acid and the amino group of another.
• Peptide bond formation is a dehydration/condensation reaction, losing a water molecule.
• Components of a polypeptide chain are called residues, the parts of the amino acid remaining after water loss.

Proteins

• Proteins are polymers or macromolecules of amino acids, ranging from a few to thousands of amino acid groups joined by peptide bonds.
• They are the most functionally diverse molecules in living systems, functioning as enzymes, hormones, antibodies, receptors and performing vital structural roles.
• Proteins are the most abundant biological macromolecules, found in all cells.
• They are highly versatile, ranging in size from small peptides to large polymers.
• Smaller proteins containing 10-40 amino acids are called polypeptides.
• Protein formation involves peptide linkage formation.
• Protein structure is crucial for function and can be disrupted (denatured) through heat or chemicals, with denatured proteins occasionally reverting (renaturation).

Protein Functions

• Proteins are vital for growth and repair.
• They perform many bodily functions like acting as enzymes, structural components, hormones, and antibodies.
• They act as structural components like keratin in hair and nail, collagen in bone.
• They are instrumental in expressing genetic information.
• They carry out tasks like oxygen and carbon dioxide transport (hemoglobin), and regulating fluid balance.
• They are involved in blood clotting, immune defense, and hereditary transmission.
• Examples of contractile proteins are actin and myosin.

Protein Classification

• Proteins are categorized based on chemical nature, structure, shape, and solubility.
• Simple proteins, on hydrolysis, yield only amino acid residues. This group includes fibrous (e.g., keratin, elastin, collagen) and globular (e.g., albumin, globulin, glutelin, histones) proteins.
• Conjugated proteins have a non-protein moiety (e.g., nucleoproteins, phosphoproteins, lipoproteins, metalloproteins).
• Derived proteins are degraded or derived products of simple or conjugated proteins, including primary derived proteins (e.g., proteans, metaproteins, coagulated proteins) and secondary derived proteins (e.g., proteoses, peptones, peptides).

Protein Structure

• Protein structure can be divided into four levels:
  • Primary: The amino acid sequence along the polypeptide chain.
  • Secondary: Local conformations (e.g., a-helices, β-sheets) formed by repeating hydrogen bonding patterns between backbone atoms.
  • Tertiary: The overall three-dimensional conformation of the protein, involving non-covalent interactions (hydrophobic interactions, electrostatic interactions, hydrogen bonds) and sometimes covalent disulfide bonds between amino acid residues.
  • Quaternary: The interaction between multiple polypeptide subunits to form a functional protein.

Protein Synthesis

• Protein synthesis involves amino acid synthesis, transcription, translation, and post-translational events.
• In amino acid synthesis, the body produces some amino acids from glucose and other metabolites, while others are obtained from the diet.
• Transcription converts DNA into mRNA, which is then used during translation to determine the amino acid sequence and create a polypeptide chain.
• Following translation, the protein undergoes further processing steps like proteolysis, post-translational modifications, and protein folding until a functional protein is produced.