General Biology and Genetics: Chemical Basis of Life

Course Overview

Objectives

This course introduces students to the foundational principles of cellular biology and genetics, focusing on molecular mechanisms, inheritance, and disease diagnosis. Students will gain an understanding of cellular structures, molecular biology concepts, genetic mutations, and diagnostic techniques, as well as participate in genetic counseling.

• Cellular structures and functions: Understanding cell proliferation and cell death.

• Molecular biology and genetics: Laws of inheritance and genetic mechanisms.

• Pathogenesis: Mechanisms related to genetic and chromosomal mutations.

• Techniques: Application of cellular and molecular biology in disease diagnosis.

• Genetic counseling: Participation in counseling for hereditary conditions.

Chapter 1: The Chemical Basis of Life

1. The Elements of Life

Life depends on a select group of chemical elements that are essential for cellular and physiological functions.

• Major elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N) make up approximately 96% of the human body.

• Minor elements: The remaining 4% includes calcium, phosphorus, potassium, sulfur, and others.

• Trace elements: Present in quantities less than 0.01%, such as iron (Fe), iodine (I), zinc (Zn), and more.

Element	Symbol	Percentage of Human Body Weight
Oxygen	O	65.0
Carbon	C	18.5
Hydrogen	H	9.5
Nitrogen	N	3.3
Calcium	Ca	1.5
Phosphorus	P	1.0
Potassium	K	0.4
Sulfur	S	0.3
Sodium	Na	0.2
Chlorine	Cl	0.2
Magnesium	Mg	0.1

2. Chemical Bonds

Chemical bonds are the forces that hold atoms together in molecules and compounds, crucial for biological structure and function.

• Covalent bonds: Atoms share electrons; can be single ($-$), double ($=$), or triple ($riple$) bonds.

• Ionic bonds: Formed between oppositely charged ions (cations and anions), e.g., NaCl.

• Weak chemical bonds:

  • Hydrogen bonds: Attraction between hydrogen and electronegative atoms (O, N).

  • Hydrophobic interactions: Nonpolar molecules aggregate to avoid water.

  • Van der Waals interactions: Weak attractions due to transient electron asymmetry.

Covalent Bonds

• Single bond: $-$ (one pair of electrons)

• Double bond: $=$ (two pairs of electrons)

• Triple bond: $\equiv$ (three pairs of electrons)

• Polar covalent bond: Unequal sharing of electrons (e.g., H2O)

• Nonpolar covalent bond: Equal sharing of electrons (e.g., O2)

Ionic Bonds

• Ion: A charged atom or molecule

• Cation: Positively charged ion

• Anion: Negatively charged ion

• Example: Sodium chloride (NaCl) formation

Weak Chemical Bonds

• Hydrogen bonds: Important in protein and nucleic acid structure

• Hydrophobic interactions: Drive formation of cell membranes

• Van der Waals interactions: Enable adhesion (e.g., gecko feet)

3. Inorganic Compounds

Inorganic compounds are vital for cellular processes and include water, acids, bases, and salts.

3.1. Water

• Most abundant component: 60-65% of adult body weight, up to 95% in fetus

• Polar molecule: Forms hydrogen bonds, enables transport and surface tension

• Hydrophilic molecules: Form hydrogen bonds with water

• Hydrophobic molecules: Do not form hydrogen bonds with water

• Roles of water:

  • 95% is free form, 5% linked to macromolecules

  • Moderates temperature, prevents sudden changes

  • Evaporative cooling

3.2. Other Inorganic Compounds

• Acids: Increase H+ concentration in solution $\mathrm{HCl \rightarrow H^+ + Cl^-}$

• Bases: Reduce H+ concentration, accept protons or produce OH- $\mathrm{NH_3 + H^+ \rightarrow NH_4^+}$ $\mathrm{NaOH \rightarrow Na^+ + OH^-}$

• pH regulation: Most biological fluids are pH 6-8; blood pH is tightly regulated around 7.4

• Buffer systems: Carbonic acid-bicarbonate system $\mathrm{H_2CO_3 \rightleftharpoons HCO_3^- + H^+}$

• Salts: NaCl, KCl, CaCl2, etc.; essential for cellular function

4. Organic Compounds

Organic compounds are the molecules of life, including carbohydrates, lipids, nucleic acids, and proteins.

4.1. Carbohydrates

• Composed of: C, H, O

• Groups:

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

  • Disaccharides: Two monosaccharides joined (e.g., lactose, maltose, saccharose)

  • Polysaccharides: Polymers of monosaccharides (e.g., starch, glycogen, cellulose, chitin)

• Functions:

  • Fuel: Glucose is the main energy source

  • Protection: Cellulose (plant cell wall), chitin (exoskeleton)

  • Cell membrane: Glycolipids and glycoproteins

Type	Example	Function
Monosaccharide	Glucose, Fructose	Energy source
Disaccharide	Lactose, Maltose	Energy source
Polysaccharide	Starch, Glycogen, Cellulose, Chitin	Storage, structure

4.2. Lipids

• Hydrophobic: Insoluble in water

• Composed of: C, H, O, P, N

• Groups:

  • Triglycerides: Glycerol + 3 fatty acids

  • Phospholipids: Glycerol + 2 fatty acids + phosphate group

  • Steroids: Four fused rings (e.g., cholesterol, hormones)

• Fatty acids:

  • Saturated: No double bonds (e.g., stearic acid)

  • Unsaturated: One or more double bonds (e.g., oleic acid, linoleic acid)

Triglyceride Formation

• Glycerol (3C alcohol) + 3 fatty acids → Triglyceride + 3 H2O (via ester bonds)

Phospholipids

• Bipolar molecules: Hydrophilic head, hydrophobic tails

• Form micelles and bilayers in water, essential for cell membrane structure

Steroids

• Structure: Four fused rings

• Examples: Cholesterol, estrogen, testosterone

Additional info:

• These notes cover the chemical basis of life, which is foundational for understanding cell structure, metabolism, and genetics in biology.