Biochemistry of Proteins and Nucleic Acids

Proteins: Structure, Composition, and Function

Amino Acids and Basic Composition

• Atomic Composition: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N).
• Sub-molecular Unit: Amino acid.
• There are 20 amino acids, 8 of which are essential.
• Amino acids bind via the Peptide Bond, resulting in the loss of a water molecule.

Amino Acid Polarity and Characteristics

• Hydrophobic Amino Acids: Water repellent (non-polar).
• Polar Amino Acids: Can form hydrogen bonds with water molecules.

Protein Sources

Meat, eggs, vegetables, and milk.

Amino Acid Color Coding (Visualization)

In certain models, amino acids are color-coded based on their properties:

• Brown: Hydrophobic Amino Acids (water repellent).
• Green: Polar Amino Acids (can form hydrogen bonds with water molecules).
• Fuchsia: Acidic Amino Acids (pH).
• Turquoise: Basic Amino Acids (pH).

Protein Structure (Conformation)

The structure determines the function of the protein.

1. Primary Structure:

   The linear sequence or configuration of amino acids (straight chain).

2. Secondary Structure:

   Local folding patterns stabilized by hydrogen bonds.

   • Alpha Helix: Spiral structure.
   • Beta-Pleated Sheet: Folded, zig-zag structure.
3. Tertiary Structure:

   The overall three-dimensional shape resulting from interactions between side chains. The chain is entangled and can contain both primary and secondary structures. Forms Random Coils or Globular Proteins.

4. Quaternary Structure:

   The union of multiple protein subunits (polypeptide chains).

   Example: Hemoglobin, which carries O₂ and CO₂.

Case Study: Hemoglobin and Anemia

Hemoglobin is a protein found in red blood cells (erythrocytes). Its primary function is Oxygen (O₂) and Carbon Dioxide (CO₂) exchange. Anemia is often associated with a lack of iron, which is crucial for hemoglobin synthesis.

Protein Functions

Structural Function

Almost all biological structures are protein-based. Examples include: Collagen, Elastin (skin), Keratin (nails/hair), and Actin/Myosin (muscles).

Enzymatic Function

Enzymes are considered biocatalysts—molecules that significantly speed up chemical reactions.

Transporter Function

Proteins located in the plasma membrane help molecules pass through via various mechanisms (e.g., the Sodium-Potassium Pump, Carrier Proteins).

Defensive Function

Antibodies are proteins released by B-lymphocytes (white blood cells) that neutralize pathogenic agents (viruses, bacteria).

Chemical Messenger Function

Some hormones are proteinaceous and regulate biological processes. Hormones are chemical substances released by a specific tissue. Example: Somatotropin (Growth Hormone).

Nucleic Acids and Genetic Material

Nucleotide Composition

Nucleic acids are formed by the union of bioelements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), and Phosphorus (P). Their most basic units are called nucleotides.

A Nucleotide consists of:

1. Nitrogenous Base
2. Pentose Sugar
3. Phosphate Group

Nucleotides link together via phosphodiester bonds.

Nitrogenous Bases

• Purines (Double Ring): Adenine (A), Guanine (G).
• Pyrimidines (Single Ring): Cytosine (C), Thymine (T), or Uracil (U).

Chromosomes and Karyotype

DNA Structure: DNA is composed of complementary strands exhibiting antiparallelism.

Cell Types and Chromosome Count

• A diploid cell contains 46 chromosomes.
• A haploid cell contains 23 chromosomes.

Chromosome Terminology

• Human Karyotype: The complete set of human chromosomes.
• Homologous Chromosomes: Chromosomes of equal size but originating from different sources (maternal and paternal).
• Heterochromosomes: Sex chromosomes (e.g., X and Y).