General Biology I: Core Concepts and Foundations – Study Notes

Life

Characteristics of Life

Living organisms share a set of fundamental characteristics that distinguish them from non-living matter. Understanding these traits is essential for identifying life and its processes.

• Evolutionary adaptation: The ability of populations to change over generations in response to environmental pressures.

• Reproduction: The process by which organisms produce new individuals of the same species.

• Growth and development: Increase in size and complexity through cell division and differentiation.

• Energy use and transformation (metabolism): The chemical processes that convert energy and matter to sustain life.

• Order / Cellular organization: Living things are composed of one or more organized cells.

• Response to stimuli: The ability to detect and respond to environmental changes.

• Homeostasis and regulation: Maintenance of stable internal conditions despite external changes.

Are viruses living? No, viruses do not meet all criteria for life. For example, they are acellular (lack cells) and do not independently carry out metabolism or homeostasis.

Biological Organization

Biological systems are organized in a hierarchy from smallest to largest:

• Atoms

• Molecules

• Cells

• Tissues

• Organs

• Organ Systems

• Population

• Community

• Ecosystem

• Biome

• Biosphere

Domains of Life

Three Domains

• Eukarya: Nucleus and other membrane-bound organelles; single or multicellular; includes kingdoms Animalia, Plantae, Fungi, and Protista.

• Bacteria: No membrane-bound organelles; always unicellular; single circular chromosome; structurally and biochemically distinct from Archaea.

• Archaea: No membrane-bound organelles; always unicellular; single circular chromosome; cell wall and membrane composition distinct from Bacteria; often extremophiles.

Note: Bacteria and Archaea are collectively called prokaryotes.

Kingdoms of Eukaryotes

• Animalia: Always multicellular

• Plantae: Always multicellular

• Fungi: Single or multicellular

• Protista: Single or multicellular

Evolution

Natural Selection and Fitness

Evolution is the process by which populations of organisms change over generations. Natural selection is the primary mechanism driving evolution.

• Natural selection: Individuals with traits that confer a fitness advantage are more likely to survive and reproduce, passing those traits to offspring.

• Fitness: The genetic contribution of an individual to the next generation. Relative fitness is measured by the number of surviving fertile offspring.

• Other mechanisms: Gene flow, genetic drift, and mutations also contribute to evolution.

Evolution acts on populations, not individuals.

Macromolecules

Functional Groups

Functional groups are specific groups of atoms within molecules that have characteristic properties and chemical reactivity.

• Hydroxyl (alcohol)

• Carboxyl (carboxylic acid)

• Amino

• Phosphate

• Ester

These groups are found in various macromolecules such as carbohydrates, lipids, proteins, and nucleic acids.

Polymers and Monomers

• Polymers: Large molecules made of repeating subunits (monomers) linked by dehydration reactions.

• Hydrolysis: Polymers can be broken down into monomers by hydrolysis reactions.

Carbohydrates

• Monomer: Monosaccharide (simple sugar)

• Disaccharide: Two monosaccharides linked together

• Polysaccharide: Polymer of monosaccharides

Functions:

• Energy storage (e.g., glycogen in animals, starch in plants)

• Structural support (e.g., cellulose in plants, chitin in fungi and arthropods)

• Cell-to-cell communication (glycoproteins, glycolipids)

Examples:

• Monosaccharides: Glucose, fructose, galactose

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

• Polysaccharides: Cellulose, starch, glycogen, chitin

Lipids

• Not true polymers; hydrophobic (nonpolar)

• Functions: Energy storage, insulation, waterproofing, cell membrane structure, cell signaling

• Types:

  • Triglycerides: Glycerol + 3 fatty acids (energy storage)

  • Phospholipids: Major component of cell membranes

  • Steroids: Cholesterol, hormones

  • Waxes: Waterproofing (e.g., leaf waxes, beeswax)

• Fatty acids: Can be saturated (no double bonds) or unsaturated (one or more double bonds)

Nucleic Acids

• Monomer: Nucleotide

• Polymer: DNA and RNA

• Functions: Store and transmit genetic information

• Nucleotide structure: Pentose sugar (ribose or deoxyribose), phosphate group, nitrogenous base

• Nitrogenous bases: Adenine (A), guanine (G), cytosine (C), thymine (T, DNA only), uracil (U, RNA only)

Base pairing in DNA:

• A pairs with T (2 hydrogen bonds)

• C pairs with G (3 hydrogen bonds)

Proteins

• Monomer: Amino acid

• Polymer: Polypeptide

• Structure: Central carbon, amino group, carboxyl group, R group (side chain), hydrogen

• Peptide bond: Formed between carboxyl group of one amino acid and amino group of another

• Levels of structure:

  • Primary: Sequence of amino acids

  • Secondary: Alpha helices and beta-pleated sheets (hydrogen bonding)

  • Tertiary: 3D folding (disulfide bridges, hydrophobic interactions, ionic bonds)

  • Quaternary: Association of multiple polypeptides (e.g., hemoglobin)

• Classification of amino acids: Acidic, basic, polar uncharged, nonpolar, special (glycine, cysteine, proline)

Cells & Prokaryotes vs. Eukaryotes

Cell Structures

• Plasma membrane: Encloses the cell, regulates entry/exit of substances

• Cytoplasm: Fluid inside the cell (cytosol + organelles)

• Ribosomes: Sites of protein synthesis

• Genetic material: DNA (or RNA in some viruses)

Surface Area vs. Volume

• As cells grow, volume increases faster than surface area

• Limits cell size; adaptations include membrane folding to increase surface area

Compartments and Organelles (Eukaryotes)

• Nucleus: Stores DNA, site of RNA synthesis

• Endoplasmic reticulum (ER): Rough ER (protein synthesis), Smooth ER (lipid synthesis)

• Golgi apparatus: Modifies, sorts, packages proteins/lipids

• Lysosomes: Digestion of macromolecules

• Peroxisomes: Breakdown of toxins

• Mitochondria: Energy production (cellular respiration)

• Chloroplasts: Photosynthesis (plants and algae)

Prokaryotes vs. Eukaryotes

Feature	Prokaryotes	Eukaryotes
Cell size	Smaller	Larger
Cellularity	Always unicellular	Single or multicellular
Organelles	No membrane-bound organelles	Membrane-bound organelles present
Genome	Single, circular chromosome	Multiple, linear chromosomes
Examples	Bacteria, Archaea	Animals, plants, fungi, protists

Chemistry

Atoms and Elements

• Element: Pure substance consisting of one type of atom

• Subatomic particles: Protons (+), neutrons (0), electrons (-)

• Atomic number: Number of protons

• Atomic mass: Number of protons + neutrons

Isotopes

• Atoms of the same element with different numbers of neutrons

• Some isotopes are radioactive and used in research/medicine

Compounds and Molecules

• Compound: Substance composed of two or more elements (e.g., H2O)

• Molecule: Two or more atoms bonded together

Periodic Table and Electronegativity

• Metals vs. non-metals: Metals are typically on the left and center; non-metals on the right

• Electronegativity: Tendency of an atom to attract electrons in a bond

• Highly electronegative elements (e.g., O, N) pull electrons strongly

Bonds

• Polar covalent bond: Electrons are shared unequally (e.g., H2O)

• Nonpolar covalent bond: Electrons are shared equally

• Ionic bond: Electrons are transferred from one atom to another

Example: In H2O, oxygen is more electronegative than hydrogen, resulting in a partial negative charge on oxygen and a partial positive charge on hydrogen.

Key Equations

• Atomic mass: $\text{Atomic mass} = \text{Number of protons} + \text{Number of neutrons}$