General Biology Study Guide: Foundations, Chemistry, Biological Molecules, and the Origin of Life

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Biological Hierarchy: Biological Systems are Structured and Interrelated

Levels of Biological Organization

Biological systems are organized into a hierarchy of levels, each with emergent properties that arise from the interactions of their components. Understanding these levels helps explain the complexity and diversity of life.

Hierarchy of Complexity: Includes molecules, organelles, cells, tissues, organs, organ systems, organisms, populations, communities, ecosystems, and the biosphere.
Emergent Properties: New characteristics that arise at each level of organization due to interactions among components (e.g., consciousness in brains, life in cells).
Example: A single neuron cannot think, but a network of neurons (the brain) can produce thought.

Experimental Design and Scientific Method

Scientists use the principles of experimental design and hypothesis testing to investigate natural phenomena and expand our understanding of the world.

Scientific Method Steps: Observation, question, hypothesis, prediction, experiment, analysis, and conclusion.
Hypothesis: A testable explanation for an observation.
Theory: A well-substantiated explanation based on a body of evidence.
Variables: Independent variable is manipulated; dependent variable is measured.
Example: Testing the effect of light on plant growth (light is independent, growth is dependent).

Cell Structure and Genetics

Prokaryotic vs. Eukaryotic Cells

Cells are the basic units of life and can be classified as prokaryotic or eukaryotic based on their structure.

Prokaryotes: Lack a nucleus and membrane-bound organelles (e.g., Bacteria, Archaea).
Eukaryotes: Have a nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).
Key Differences: Size, complexity, presence of organelles, and DNA organization.

Genetic Material: DNA, Genes, Chromosomes, and Genome

DNA (Deoxyribonucleic Acid): The molecule that stores genetic information.
Gene: A segment of DNA that codes for a specific protein or function.
Chromosome: A structure composed of DNA and proteins that contains many genes.
Genome: The complete set of genetic material in an organism.

Gene Expression

Transcription: The process of copying a gene's DNA sequence into messenger RNA (mRNA).
Translation: The process where ribosomes use mRNA to synthesize proteins.
Central Dogma:

Principles of Evolution by Natural Selection

Evolution and Diversity of Life

Evolution explains the unity and diversity of life through the process of natural selection.

Natural Selection: The process by which organisms with advantageous traits survive and reproduce more successfully.
Adaptation: Traits that increase an organism's fitness in a particular environment.
Tree of Life: Illustrates the evolutionary relationships among all living organisms, divided into three domains: Bacteria, Archaea, and Eukarya.

Chemistry for Biology: Structure and Properties of Molecules

Atoms and Elements

All matter is composed of atoms, which combine to form molecules essential for life.

Major Elements in Biology: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Sulfur (S).
Atomic Structure: Atoms consist of protons, neutrons, and electrons.
Isotopes: Atoms of the same element with different numbers of neutrons.

Chemical Bonds

Covalent Bonds: Atoms share electrons (can be polar or nonpolar).
Ionic Bonds: Transfer of electrons from one atom to another, forming charged ions.
Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., O or N).
Van der Waals Interactions: Weak attractions due to transient charge differences.
Example: Water molecules form hydrogen bonds, giving water its unique properties.

Properties of Water

Cohesion and Adhesion: Water molecules stick to each other and to other surfaces.
High Specific Heat: Water resists temperature changes.
High Heat of Vaporization: Water requires a lot of energy to evaporate.
Density: Ice is less dense than liquid water, so it floats.
Solvent Properties: Water dissolves many substances due to its polarity.

Acids, Bases, and pH

pH Scale: Measures the concentration of hydrogen ions () in a solution.
Equation:
Acids: Donate hydrogen ions; Bases: Accept hydrogen ions.
Buffers: Substances that minimize changes in pH.

Biological Molecules: Structure and Function

Macromolecules and Monomers

Cells are made up of four major classes of biological macromolecules: carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates: Monomers are monosaccharides (e.g., glucose); function in energy storage and structure.
Lipids: Include fats, oils, phospholipids, and steroids; hydrophobic and function in energy storage, membranes, and signaling.
Proteins: Polymers of amino acids; function in catalysis, structure, transport, and regulation.
Nucleic Acids: DNA and RNA; store and transmit genetic information.

Polymerization and Hydrolysis

Dehydration Synthesis: Monomers are joined by removing water.
Hydrolysis: Polymers are broken down by adding water.

Protein Structure

Primary Structure: Sequence of amino acids.
Secondary Structure: Alpha helices and beta sheets formed by hydrogen bonding.
Tertiary Structure: 3D folding due to side chain interactions.
Quaternary Structure: Association of multiple polypeptide chains.
Denaturation: Loss of structure (and function) due to changes in temperature, pH, or environment.

Nucleic Acids: DNA and RNA

DNA: Double helix, stores genetic information, bases are A, T, C, G.
RNA: Single-stranded, involved in protein synthesis, bases are A, U, C, G.
Base Pairing: A-T (or A-U in RNA), C-G.
Directionality: 5' to 3' ends in nucleic acids.

Origin of Life: Chemical Evolution

Hypotheses for the Origin of Life

The first living cells are thought to have originated by chemical evolution in the pre-biotic Earth.

Abiotic Synthesis: Formation of organic molecules from inorganic precursors under early Earth conditions.
RNA World Hypothesis: Suggests RNA was the first hereditary molecule due to its ability to store information and catalyze reactions.
Endosymbiosis: Theory that mitochondria and chloroplasts originated from free-living prokaryotes engulfed by ancestral eukaryotic cells.
Evidence for Endosymbiosis: Mitochondria and chloroplasts have their own DNA, double membranes, and similarities to certain bacteria.

Table: Comparison of Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Size	Small (1-10 μm)	Larger (10-100 μm)
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Key Terms and Concepts

Genome, Proteomics, Deoxyribonucleic Acid (DNA), Gene, RNA, Inheritance, Zygote, Fertilization, Negative Feedback, Global Climate Change, Tree of Life, Darwin, Natural Selection
Isotope, Covalent Bond, Ionic Bond, Hydrogen Bond, Hydrophobic Interaction, Monomer, Polymer, Dehydration Synthesis, Hydrolysis, Amino Acid, Peptide Bond, Denaturation, Nucleotide, Phosphodiester Bond, Double Helix, Base Pairing

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard General Biology curriculum.