Protein Structure Quiz

Protein Structure

• Proteins are composed of amino acids
• Twenty common structural amino acids exist
• Amino acid side chains have functional importance
• Peptide bonds link amino acids together
• Peptide bond formation involves the nitrogen and oxygen atoms, enabling hydrogen bonding with other peptide units
• Proteins have a-helix and β-pleated sheet structures
• The a-helix is a regular right-handed helix, stabilized by hydrogen bonds
• R groups (side chains) are positioned on the outside of the a-helix
• The β-pleated sheet forms from linear polypeptide chains linked by hydrogen bonds
• Antiparallel and parallel β sheets exist
• Collagen forms a triple helix, with three polypeptide chains, hydrogen-bonded together
• This helix is left-handed, with Gly-X-Y repeated sequences, where X is usually proline and Y is usually hydroxyproline
• Proteins often contain both α-helices and β-sheets to achieve their optimal structure and function
• The primary structure of a protein (the sequence of amino acids) determines its three-dimensional structure
• The three-dimensional structure is stabilized by several forces:
  • Covalent bonds (like disulfide bridges)
  • Non-covalent bonds and interactions
    • Hydrogen bonds
    • Electrostatic interactions
    • Van der Waals forces
    • Hydrophobic effect
• Protein folding is the process by which a protein assumes its functional three-dimensional structure
• Proteins can be denatured by pH, temperature, and ionic strength
• Normal protein folding is essential for various functions and aberrant folding can lead to disease.

Protein Folding

• Proteins adopt unique 3D structures determined by their amino acid sequence, essential for function
• Proteins fold spontaneously into stable conformations
• Proteins tend to fold to the conformation with the lowest energy state

Protein Structure and Function

• Proteins have different functions (structural, enzymatic, transport, etc.)
• Proteins with functions like hemoglobin, actin, and myosin illustrate the varied combinations of α-helices and β-sheets in different proteins
• Fibrous proteins (like silk) are characterized by high tensile strength but lack elasticity, due to high β sheet content
• Different protein combinations, such as hemoglobin with ≈60% alpha helix, and significant β sheet content further illustrate the functional diversity

Protein Structure - Tertiary Structure

• The tertiary structure describes how a polypeptide chain folds
• Tertiary structure typically involves several supersecondary structural elements
• Specific amino acids and interactions within the protein influence its folding
• Supersecondary structures are domains within a protein that may contain more than one type of secondary structure

Protein Structure - Quaternary Structure

• Quaternary structures involve multiple polypeptide chains interacting to form a complete functional protein
• Hemoglobin, with its alpha and beta subunits, is an example of a protein with a quaternary structure
• Multiple subunit proteins are common in biological systems

Post-Translational Modifications

• Proteins undergo modifications after synthesis (post-translational)
  • Disulfide bonds help join subunits
  • Glycosylation (addition of carbohydrate) is a critical post-translational modification,
  • O-linked glycosylations occur on hydroxyl groups of serine and threonine amino acids
  • N-linked glycosylations append sugars to the amide groups of asparagine residues

Related to Human Disease

• Protein folding and structure are pivotal in various human diseases arising from aberrant folding,
• Misfolding, aggregation of proteins contributing to neurodegenerative diseases