Notes on Proteins and Nucleic Acids

Proteins: Structure and Function

  • Composition:

    • Proteins are macromolecules made up of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.
    • They are essential for nearly all biological processes.

  • Categories and Functions of Proteins:

    • Gene Expression and Regulation:
    • Functions: Synthesize mRNA from DNA, synthesize polypeptides, and regulate gene expression.
    • Example: RNA polymerase helps synthesize RNA from DNA.
    • Motor Proteins:
    • Function: Initiate movement.
    • Example: Myosin provides contractile force in muscles.
    • Defense Proteins:
    • Function: Protect against disease.
    • Example: Antibodies destroy pathogens.
    • Metabolic Enzymes:
    • Function: Speed up chemical reactions crucial for metabolism.
    • Example: Hexokinase is involved in glucose metabolism.
    • Cell-Signaling Proteins:
    • Function: Enable communication between cells and environmental sensing.
    • Example: Notch proteins coordinate cell growth in development.
    • Structural Proteins:
    • Function: Provide support and strength.
    • Examples: Actin shapes the cytoplasm; collagen strengthens tendons.
    • Transporters:
    • Function: Mediate movement of substances across cell membranes.
    • Example: Glucose transporters facilitate glucose entry into cells.

Amino Acids: Building Blocks of Proteins

  • Amino Acid Structure:
    • Consists of an alpha-carbon linked to an amino group (─NH), a carboxyl group (─COOH), a hydrogen, and a side chain (R).
    • At neutral pH:
    • The amino group accepts a proton (becomes positively charged).
    • The carboxyl group donates a proton (becomes negatively charged).
    • Classification of the 20 amino acids based on side-chain properties:
    • Nonpolar
    • Polar uncharged
    • Polar charged
  • Importance of Side Chains:
    • Side chain properties influence protein folding and functionality.
    • Specific side chains in enzymes are essential for catalytic functions.

Protein Synthesis: Formation of Peptide Bonds

  • Peptide Bond Formation:
    • Amino acids join via a dehydration reaction (lose water) between the carboxyl group of one and the amino group of another, forming a peptide bond.
    • This process occurs during translation, leading to polypeptide formation.

Nucleic Acids: DNA and RNA

  • Nucleic Acids:
    • Essential macromolecules for genetic information storage, expression, and transmission.
  • Nucleotide Composition:
    • Each nucleotide consists of:
    1. Phosphate group
    2. Pentose sugar (deoxyribose in DNA and ribose in RNA)
    3. Nitrogenous base (single or double-ringed structures)
  • DNA vs. RNA:
    • DNA stores genetic information, while RNA decodes it for protein synthesis.

Key Takeaways

  • Proteins serve diverse functions ranging from structural support to enzymatic activity.
  • The unique sequence and properties of amino acids within proteins determine their 3D structure and biological role.
  • Nucleic acids play a crucial role in carrying genetic information and are vital for protein synthesis.