Core Principles and Foundations of Biology: Study Notes

Evolution, the Themes of Biology, and Scientific Inquiry

Biological Organization and Classification

Biology is the study of life, which is organized into hierarchical levels, from atoms to the biosphere. Classification systems help organize the diversity of life, grouping organisms based on shared characteristics and evolutionary relationships.

• Taxonomic Hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

• Domains of Life: Bacteria, Archaea, and Eukarya.

• Core Theme: Evolution explains the unity and diversity of life, with all organisms descended from common ancestors.

• Emergent Properties: New properties arise at each level of organization due to the arrangement and interaction of parts.

Themes of Biology

• Interaction: Organisms interact with their environment, exchanging matter and energy.

• Cells: The basic unit of structure and function in living organisms. Two main types: prokaryotic (no nucleus) and eukaryotic (nucleus present).

• Structure and Function: Biological structures are closely related to their functions.

• Feedback Mechanisms: Regulate biological systems (e.g., homeostasis).

Levels of Biological Organization

Life is organized into a hierarchy, from the smallest chemical units to the entire biosphere.

• Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → Organisms → Populations → Communities → Ecosystems → Biosphere

The Chemical Context of Life

Atoms, Elements, and Chemical Bonds

All matter is composed of atoms, which consist of protons, neutrons, and electrons. Chemical bonds form when atoms interact to achieve stability.

• Covalent Bonds: Sharing of electron pairs between atoms (strong bond).

• Ionic Bonds: Transfer of electrons from one atom to another, resulting in oppositely charged ions (strong bond).

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

• Van der Waals Interactions: Weak attractions due to transient charge differences.

Water and Life

Properties of Water

Water is essential for life due to its unique chemical and physical properties, which arise from its polarity and ability to form hydrogen bonds.

• Cohesion: Water molecules stick together via hydrogen bonds.

• Temperature Moderation: Water absorbs and releases heat slowly, stabilizing temperatures.

• Expansion Upon Freezing: Ice is less dense than liquid water, allowing it to float.

• Versatility as a Solvent: Water dissolves many substances, facilitating chemical reactions in cells.

Acids, Bases, and pH

The pH scale measures the concentration of hydrogen ions (H+) in a solution. Acids increase H+ concentration, while bases decrease it. Buffers help maintain stable pH in biological systems.

• Acid: Substance that donates H+ ions (e.g., HCl).

• Base: Substance that accepts H+ ions or donates OH- (e.g., NaOH).

• Buffer: Substance that minimizes changes in pH by reversibly binding H+.

Carbon and the Molecular Diversity of Life

Carbon Skeletons and Functional Groups

Carbon atoms form the backbone of biological molecules, creating diverse structures such as chains, branches, and rings. Functional groups attached to carbon skeletons determine the properties and reactivity of organic molecules.

• Structural Diversity: Length, branching, double bond position, and ring formation.

• Common Functional Groups: Hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, methyl.

The Structure and Function of Large Biological Molecules

Macromolecules and Polymers

Large biological molecules, or macromolecules, include carbohydrates, proteins, nucleic acids, and lipids. Most macromolecules are polymers, built from monomers by dehydration reactions and broken down by hydrolysis.

• Dehydration Reaction: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

Carbohydrates

Carbohydrates serve as fuel and building material. They include monosaccharides (simple sugars), disaccharides, and polysaccharides.

• Monosaccharides: Glucose, fructose, ribose, etc.

• Disaccharides: Sucrose, lactose, maltose.

• Polysaccharides: Starch, glycogen, cellulose, chitin.

Lipids

Lipids are hydrophobic molecules, including fats, phospholipids, and steroids. They are important for energy storage, membrane structure, and signaling.

• Fats (Triglycerides): Glycerol + 3 fatty acids, used for energy storage.

• Phospholipids: Major component of cell membranes, with hydrophilic heads and hydrophobic tails.

• Steroids: Lipids with a carbon skeleton of four fused rings (e.g., cholesterol).

Proteins

Proteins are polymers of amino acids and perform a vast array of functions, including catalysis, structure, transport, and signaling. Protein structure is organized into four levels: primary, secondary, tertiary, and quaternary.

• Amino Acid Structure: Central carbon, amino group, carboxyl group, side chain (R group).

• Levels of Structure:

  • Primary: Sequence of amino acids

  • Secondary: Alpha helices and beta sheets

  • Tertiary: 3D folding

  • Quaternary: Multiple polypeptides

Nucleic Acids

Nucleic acids store and transmit genetic information. DNA and RNA are polymers of nucleotides, each consisting of a sugar, phosphate group, and nitrogenous base.

• DNA: Double helix, stores genetic information.

• RNA: Single-stranded, involved in protein synthesis.

• Central Dogma: DNA → RNA → Protein

A Tour of the Cell

Cell Structure and Function

Cells are the fundamental units of life. Eukaryotic cells contain membrane-bound organelles, while prokaryotic cells do not. Key organelles include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and (in plants) chloroplasts and central vacuole.

• Nucleus: Contains genetic material (DNA).

• Mitochondria: Site of cellular respiration and ATP production.

• Chloroplasts: Site of photosynthesis in plants.

• Endoplasmic Reticulum (ER): Synthesis of proteins (rough ER) and lipids (smooth ER).

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Digestion and waste removal (animal cells).

• Cell Wall: Provides structure and support (plants, fungi, some protists).

Membrane Structure and Function

Plasma Membrane Structure

The plasma membrane is a selectively permeable barrier composed of a phospholipid bilayer with embedded proteins, carbohydrates, and cholesterol. It regulates the movement of substances into and out of the cell.

• Fluid Mosaic Model: Membrane is flexible, with proteins floating in or on the lipid bilayer.

• Membrane Proteins: Integral (span the membrane) and peripheral (attached to surface).

• Carbohydrates: Involved in cell recognition and signaling.

Transport Across Membranes

Cells transport substances across membranes via passive and active mechanisms.

• Passive Transport: Movement down a concentration gradient (diffusion, osmosis, facilitated diffusion).

• Active Transport: Movement against a concentration gradient, requiring energy (ATP).

• Osmosis: Diffusion of water across a selectively permeable membrane.

An Introduction to Metabolism

Energy and Enzymes

Metabolism encompasses all chemical reactions in a cell. Enzymes are biological catalysts that speed up reactions by lowering activation energy.

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

• Second Law of Thermodynamics: Energy transformations increase entropy (disorder).

• Enzyme Activity: Affected by temperature, pH, cofactors, and inhibitors.

Cellular Respiration and Fermentation

Overview of Cellular Respiration

Cellular respiration is the process by which cells extract energy from glucose to produce ATP. It includes glycolysis, the citric acid cycle, and oxidative phosphorylation.

• Glycolysis: Occurs in the cytosol; breaks glucose into pyruvate.

• Citric Acid Cycle: Completes the breakdown of glucose in the mitochondria.

• Oxidative Phosphorylation: Electron transport chain and chemiosmosis produce most ATP.

• Fermentation: Anaerobic process producing lactate or ethanol when oxygen is absent.

The Cell Cycle and Cell Division

Mitosis and Meiosis

Cell division is essential for growth, development, and reproduction. Mitosis produces genetically identical cells, while meiosis produces gametes with half the chromosome number.

• Mitosis: Division of somatic cells; stages include prophase, metaphase, anaphase, telophase, and cytokinesis.

• Meiosis: Division of germ cells; reduces chromosome number by half, generating genetic diversity.

• Binary Fission: Prokaryotic cell division.

The Molecular Basis of Inheritance

DNA Replication, Transcription, and Translation

Genetic information is stored in DNA and expressed through the processes of replication, transcription, and translation.

• DNA Replication: Semi-conservative process producing two identical DNA molecules.

• Transcription: Synthesis of RNA from a DNA template.

• Translation: Synthesis of proteins from mRNA by ribosomes.

Additional info: These notes cover foundational topics from the first several chapters of a college-level biology course, including cell structure, macromolecules, metabolism, and genetics. For further study, refer to the specific chapters in your textbook for more detail and examples.