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.