Biological Elements and Molecules

Biological Elements and Molecules in Cellular Functions and Control

Introduction to Biological Elements and Their Roles

• Understanding the chemical composition of cells is essential for exploring biological control methods for freshwater snails.

• Key questions include:

  • What is the chemical composition of a cell?

  • What are the properties of water and its importance in cells?

  • What are the elements found in carbohydrates, proteins, lipids, and nucleic acids?

  • How are polymers produced from monomers?

  • What is the importance of these macromolecules (carbohydrates, proteins, lipids, nucleic acids) in a cell?

Chapter 4: Chemical Composition in a Cell

4.1 Water

• 4.1.1 Properties of Water Molecule

  • Water ($H_2O$) is a polar molecule due to the unequal sharing of electrons between oxygen and hydrogen.

  • The polarity of water molecules leads to the formation of hydrogen bonds.

• 4.1.2 Importance of Water in Cells

  • Universal Solvent: Water's polarity allows it to dissolve various solutes, essential for biochemical reactions within cells.

  • Cohesion and Adhesion: Water molecules exhibit cohesive forces (attraction to themselves) and adhesive forces (attraction to other substances), enabling capillary action—important in xylem tubes for water transport in plants.

  • High Specific Heat Capacity: Water requires 4.2 kJ to raise the temperature of 1 kg by 1°C, which helps maintain stable body temperatures in organisms.

4.2 Carbohydrates

• 4.2.1 Chemical Elements in Carbohydrates

  • Carbohydrates consist of carbon (C), hydrogen (H), and oxygen (O) in the ratio 1:2:1; general formula is $C_n(H_2O)_n$.

• 4.2.2 Types of Carbohydrates

  • Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose).

  • Disaccharides: Formed from two monosaccharides (e.g., sucrose, maltose, lactose).

  • Polysaccharides: Complex carbohydrates formed from many monosaccharides (e.g., starch, glycogen, cellulose).

• 4.2.3 Formation and Breakdown

  • Formation: Condensation reactions link monosaccharides to form disaccharides and polysaccharides, removing a water molecule.

  • Breakdown: Hydrolysis involves the addition of water to break down disaccharides and polysaccharides into their monosaccharide units.

  • Example reactions:

    • $ext{Glucose} + ext{fructose} <br>ightarrow ext{sucrose} + ext{H}_2O$ (Condensation)

    • $ext{sucrose} + ext{H}_2O <br>ightarrow ext{glucose} + ext{fructose}$ (Hydrolysis)

• 4.2.4 Importance of Carbohydrates

  • Source of energy: For metabolism and cellular respiration (e.g., glucose).

  • Structural role: Cellulose in plant cell walls provides rigidity.

  • Storage: Glycogen in animals; starch in plants.

4.3 Proteins

• 4.3.1 Chemical Elements in Proteins

  • Composed mainly of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). Some also contain sulfur (S) and phosphorus (P).

• 4.3.2 Formation and Breakdown

  • Dipeptides: Formed by two amino acids linked by a peptide bond through condensation (removing water).

  • Polypeptides: Chains of amino acids can form a single protein.

• 4.3.3 Importance of Proteins

  • Structural roles: Keratin in skin, collagen in bones, and myosin in muscles.

  • Functional roles: Enzymes catalyze biological reactions, antibodies for immune response, transport proteins (e.g., hemoglobin).

4.4 Lipids

• 4.4.1 Chemical Elements in Lipids

  • Composed of carbon (C), hydrogen (H), and oxygen (O), with a higher hydrogen to oxygen ratio compared to carbohydrates.

• 4.4.2 Types of Lipids

  • Triglycerides: Formed from glycerol and three fatty acids.

  • Phospholipids: Major components of cell membranes, composed of glycerol, fatty acids, and phosphate.

  • Steroids: Lipids with a fused ring structure (e.g., cholesterol).

• 4.4.3 Importance of Lipids

  • Reserve energy, protection for organs, thermal insulation, waterproofing (waxes), and cell membrane structure (phospholipids).

4.5 Nucleic Acids

• 4.5.1 Chemical Elements

  • Made of carbon (C), hydrogen (H), nitrogen (N), oxygen (O), and phosphorus (P).

• 4.5.2 Structure of Nucleotides

  • Composed of a pentose sugar (ribose or deoxyribose), a nitrogenous base (A, T, C, G for DNA; A, U, C, G for RNA), and a phosphate group.

• 4.5.3 Types of Nucleic Acids

  • DNA: Double-stranded, stores genetic information.

  • RNA: Single-stranded, involved in protein synthesis (mRNA, rRNA, tRNA).

• 4.5.4 Importance of Nucleic Acids

  • Genetic material carriers, blueprints for protein synthesis, and necessary for cell division and inheritance.

• 4.5.5 Chromosome Formation

  • DNA wraps around histones to form nucleosomes, which further coil to form chromosomes.

Summary of Key Principles

1. Properties of water: Polarity, specific heat, adhesion, and cohesion are critical for cellular functions.

2. Carbohydrates: Source of energy, storage, and structural components in cells.

3. Proteins: Enzymatic and structural functions, composed of amino acids.

4. Lipids: Energy storage, membrane formation, and signaling molecules.

5. Nucleic acids: Genetic information storage and transmission through DNA and RNA structures.