Chapter 1: Introduction to Biology

Key Concepts in Biology

Biology is the scientific study of life, encompassing a wide range of topics from molecular mechanisms to ecosystem dynamics. Understanding foundational concepts is essential for further study in the biological sciences.

• Selective Pressure: An environmental factor that favors the survival or reproduction of certain traits over others, driving evolution.

• Taxonomy: The classification of organisms into hierarchical groups (Domain → Species).

• Gene: A segment of DNA that codes for a protein or RNA molecule.

• Scientific Theory: A broad, well-supported explanation of natural phenomena.

• Hypothesis: A testable, falsifiable explanation for an observation.

• Quantitative Data: Numerical data (e.g., mass, temperature).

• Qualitative Data: Descriptive data (e.g., color, shape).

• Evolution: Change in populations over time due to natural selection and other mechanisms.

• Natural Selection: Individuals with advantageous traits survive and reproduce more successfully.

• Eukaryote: Cells with nuclei and organelles.

• Prokaryote: Cells without nuclei or organelles.

• Nucleus: Membrane-bound structure containing DNA in eukaryotes.

• Cytoplasm: Fluid region containing organelles.

• Genome: All DNA in an organism.

• Autosome: Non-sex chromosome (22 pairs in humans).

• Deductive Reasoning: General principle → specific observations.

• Inductive Reasoning: Specific observations → general principle.

Darwin's Key Observations

1. Variation exists among individuals.

2. Traits are inherited.

3. More offspring are produced than can survive (competition).

Domains of Life

• Bacteria: Prokaryotes, diverse.

• Archaea: Prokaryotes, extremophiles.

• Eukarya: Eukaryotes, includes animals, plants, fungi, protists.

Central Dogma of Molecular Biology

• DNA → RNA → Protein

Example: In humans, DNA is organized into 22 pairs of autosomes and 1 pair of sex chromosomes.

Chapter 2: Chemistry Basics

Atoms and Chemical Bonds

Understanding the chemical basis of life is essential for studying biological processes. Atoms, the basic units of matter, interact through chemical bonds to form molecules.

• Subatomic Particles: Proton (p), Neutron (n), Electron (e-).

• Atomic Number: Number of protons; Atomic Mass: Protons + neutrons.

• Electron Shells: Energy levels; electrons farther out have higher potential energy.

• Valence Shell: Outermost shell; determines bonding.

• Electronegativity: Atom's pull on electrons.

Types of Chemical Bonds

• Covalent: Atoms share electrons (e.g., CH4).

• Nonpolar Covalent: Equal sharing (e.g., H2).

• Polar Covalent: Unequal sharing (e.g., H2O).

• Ionic: Transfer of electrons; forms cations (+) and anions (−) (e.g., Na+ and Cl−).

• Hydrogen Bond: Attraction between a hydrogen atom and an electronegative atom (e.g., H in H2O).

• Van der Waals: Weak, temporary forces.

Chemical Reactions

• Reactants: Starting materials.

• Products: Resulting substances.

Chapter 3: Water & Life

Properties of Water

Water's unique properties are critical for life, influencing biological structure and function.

• Cohesion: Water molecules stick together via hydrogen bonds; important for transport in plants.

• Adhesion: Water molecules stick to other substances.

• Surface Tension: Difficulty of breaking water's surface; high due to hydrogen bonding.

• Specific Heat: Water resists temperature change, moderating Earth's climate.

• Heat of Vaporization: Energy required to convert water from liquid to gas.

• Ice Floats: Solid water is less dense than liquid, insulating aquatic life.

• Solvent of Life: Water dissolves many substances, facilitating chemical reactions.

Important Quantities

• Avogadro's Number: molecules = 1 mole.

• Molarity (M):

• Acids: Release ; Bases: Accept .

• pH Scale: ; 7 = neutral, <7 = acidic, >7 = basic.

• Buffers: Resist pH changes (e.g., carbonic acid in blood).

Chapter 4: Carbon & Molecular Diversity

Carbon Chemistry and Functional Groups

Carbon's ability to form four covalent bonds allows for a vast diversity of organic molecules, which are the basis of life.

• Hydrocarbons: Molecules of only C & H; energy-rich, hydrophobic.

• Isomers: Compounds with the same formula but different structures.

• Cis-Trans Isomers: Differ in arrangement around a double bond.

• Enantiomers: Mirror-image isomers; important in pharmaceuticals.

• Chirality: Chiral = non-superimposable mirror image; achiral = superimposable.

Functional Groups

Functional groups confer specific chemical properties to organic molecules.

• Hydroxyl (–OH)

• Carbonyl (C=O)

• Carboxyl (–COOH)

• Amino (–NH2)

• Sulfhydryl (–SH)

• Phosphate (–PO4)

• Methyl (–CH3)

Chapter 5: Macromolecules

Major Biological Macromolecules

Macromolecules are large, complex molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates

• Monomer: Monosaccharides (e.g., glucose, fructose).

• Disaccharides: Sucrose (glucose + fructose), lactose (glucose + galactose), maltose.

• Polysaccharides: Starch (plants, energy storage), glycogen (animals, branched, energy storage), cellulose (plants, structure, indigestible to humans), chitin (exoskeletons, fungal cell walls).

• Dehydration Reaction: Joins monomers by removing .

• Hydrolysis: Breaks polymers by adding .

Lipids

• Not true polymers; all hydrophobic.

• Fats (triglycerides): Glycerol + 3 fatty acids.

• Saturated Fats: Straight chains, solid at room temperature.

• Unsaturated Fats: Double bonds, bent, liquid at room temperature.

• Trans Fats: Unhealthy, artificially produced.

• Phospholipids: Glycerol + 2 fatty acids + phosphate; amphipathic; form cell membranes.

• Steroids: 4 fused carbon rings (e.g., cholesterol, hormones).

Proteins

• Monomer: Amino acids (20 types).

• Functions: Enzymes, structural support, storage, transport, defense, hormones, receptors, movement.

• Levels of Structure:

  1. Primary: Sequence of amino acids.

  2. Secondary: Alpha helices and beta sheets (hydrogen bonding).

  3. Tertiary: 3D folding (R-group interactions).

  4. Quaternary: Multiple polypeptides.

• Folding is critical: Misfolding can cause diseases (e.g., sickle cell anemia, prions).

• Post-translational Modifications: Chemical changes (e.g., phosphorylation, methylation).

Nucleic Acids

• Monomer: Nucleotide (sugar + phosphate + base).

• DNA: Stores hereditary information; double helix; antiparallel strands.

• RNA: Single-stranded; various roles (mRNA, tRNA, rRNA, miRNA).

• mRNA: Carries genetic message.

• tRNA: Brings amino acids during translation.

• rRNA: Forms ribosome structure.

• miRNA: Regulates gene expression.

• Bases: Purines (A, G); Pyrimidines (C, T, U).

• Base Pairing: A–T (2 H-bonds), C–G (3 H-bonds); A–U in RNA.

• Bond: Phosphodiester linkage.

• Directionality: Always built 5' → 3'.

• DNA Mutations: Source of variation and evolution.