Amino Acids and Proteins Quiz

Amino Acids and Proteins

• Proteins make up 50% of the body's weight
• Protein's 3D structure is key to its function
• Proteins are linear polymers made of amino acids
• The amino acid sequence is determined by DNA's genetic information.

General Characteristics

• DNA → mRNA (Transcription) → Amino acid chain → Folded protein (Translation)
• The order of amino acids is crucial for how proteins function
• Different amino acids have distinctly different structures and properties.

General Characteristics (continued)

• Primary structure: The sequence of amino acids.
• Secondary structure: Local arrangements (alpha-helix, beta-sheet).
• Tertiary structure: The overall 3D shape of a protein.
• Quaternary structure: The arrangement of multiple polypeptide chains (if present).

Protein Classification

• Simple proteins: No additional components.
• Conjugated proteins: Proteins with additional components (e.g., glycoproteins, lipoproteins).
• Fibrous proteins: Long, fibrous shape (e.g., collagen).
• Globular proteins: Globular shape (e.g., albumin, globulin).

Protein Functions

• Enzymatic: Catalyze reactions (e.g., enzymes).
• Storage: Store amino acids (e.g., ovalbumin).
• Hormonal: Regulate bodily functions (e.g., hormones).
• Motor: Involved in movement (e.g., muscle proteins).
• Gene Expression Regulation: control gene activity.
• Transport: Carry molecules (e.g., hemoglobin).
• Defensive: Protect against pathogens (e.g., antibodies).
• Structural: Main structural components (e.g., collagen).

Amino Acids - Classification

• Common amino acids: 20 types, coded in DNA, major components of proteins.
• Derived amino acids: Common amino acids modified after incorporation into a protein.
• Non-protein amino acids: Not part of proteins; have specific functions.

Common Amino Acids - Structure

• Carboxyl group and amino group bonded to the same alpha carbon.
• Differ in side chains (R groups).
• R groups vary in size and charge.

Common Amino Acids - Classification

• Five main classes based on R groups' properties:
  • Nonpolar (hydrophobic): Core of proteins.
  • Polar (hydrophilic): Surface of proteins.
  • Uncharged: Hydrophilic.
  • Acidic: Negatively charged.
  • Basic: Positively charged.

Common Amino Acids - Chemical Properties

• Stereochemistry: The alpha carbon is a chiral center, meaning it has four different groups bonded to it, leading to L and D isomers. L-forms are found in proteins.
• Amphoteric molecules: Amino acids can act as both acids and bases due to their amino and carboxyl groups, forming zwitterions.
• Acid-base titration: Shows pKa values (dissociation constants) & pI (isoelectric point). These indicate the pH ranges where the amino acid exists as a neutral zwitterion.

Peptide Bond

• Two amino acids join via a dehydration reaction to form a peptide bond.
• Peptide bonds are planar, stable, and can participate in hydrogen bonds, influencing protein folding.

Protein Structural Levels (Summary)

• Primary: Amino acid sequence.
• Secondary: Local folding patterns (alpha-helix, beta-sheet).
• Tertiary: Overall 3D shape of a single polypeptide.
• Quaternary: 3D structure of a protein with multiple polypeptide chains.

Denaturation

• Denaturing agents (pH, heat, detergents) cause proteins to unfold, losing their function.
• Renaturation is the refolding of a denatured protein back to its native, functional state. (sometimes proteins cannot refold.)

Test your knowledge on amino acids and proteins, including their structures and classifications. Understand the importance of the amino acid sequence and how it determines protein function. Dive into the different levels of protein structure from primary to quaternary.