General Biology Exam 1 Review: Foundations, Chemistry of Life, and Cell Structure

Chapter 1: Themes and Methods in Biology

Major Themes of Life

Biology is the study of living organisms and their interactions with the environment. Understanding the major themes of life helps organize biological knowledge.

• Five Categories of Life: Organization, Information, Energy and Matter, Interactions, Evolution.

• Levels of Biological Organization: Biosphere → Ecosystem → Community → Population → Organism → Organ System → Organ → Tissue → Cell → Organelle → Molecule.

Scientific Method

The scientific method is a systematic approach to understanding the natural world through observation, hypothesis formation, experimentation, and analysis.

• Observation: Gathering information about phenomena.

• Hypothesis: A testable explanation for an observation.

• Experiment: A controlled method to test hypotheses.

• Controlled Experiment: An experiment in which only one variable is changed at a time, while all others are kept constant.

Chapter 2: Chemistry of Life

Atoms and Elements

All matter is composed of atoms, which are the smallest units of elements. The properties of elements are determined by their atomic structure.

• Atomic Number: Number of protons in an atom; defines the element.

• Mass Number: Sum of protons and neutrons in the nucleus.

• Electron Configuration: Electrons fill shells in a specific order (2 in the first shell, 8 in the second, etc.).

• Valence Electrons: Electrons in the outermost shell; determine chemical reactivity.

• Unpaired Electrons: Atoms with unpaired electrons in their valence shell are more likely to form bonds.

Types of Chemical Bonds

Atoms interact to achieve stable electron configurations, forming different types of chemical bonds.

• Covalent Bonds: Atoms share electron pairs (e.g., H2, O2).

• Ionic Bonds: Atoms transfer electrons, resulting in charged ions that attract each other (e.g., NaCl).

• Hydrogen Bonds: Weak attractions between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom (e.g., between water molecules).

Properties of Water

Water's unique properties are essential for life and result from its polar covalent bonds and hydrogen bonding.

• Cohesion: Water molecules stick to each other.

• Adhesion: Water molecules stick to other substances.

• High Specific Heat: Water resists temperature changes.

• Evaporative Cooling: As water evaporates, it removes heat from surfaces.

Acids, Bases, and pH

The pH scale measures the concentration of hydrogen ions (H+) in a solution.

• Acid: Substance that increases H+ concentration in solution (pH < 7).

• Base: Substance that decreases H+ concentration (pH > 7).

• Neutral Solution: pH = 7.

$\text{pH} = -\log_{10}[\text{H}^+]$

• Buffers: Substances that minimize changes in pH by accepting or donating H+ ions.

Chapter 3: Biological Molecules

Isomers

Isomers are molecules with the same molecular formula but different structures and properties.

• Structural Isomers: Differ in covalent arrangement of atoms.

• Cis-Trans Isomers: Differ in spatial arrangement around double bonds.

• Enantiomers: Mirror images of each other; important in biological activity.

Macromolecules: Structure and Function

Living organisms are composed of four major classes of macromolecules: carbohydrates, proteins, nucleic acids, and lipids.

• Carbohydrates: Energy storage and structural support.

  • Monomer: Monosaccharides (simple sugars, e.g., glucose).

  • Polymer: Polysaccharides (e.g., starch, glycogen, cellulose).

• Proteins: Catalyze reactions, structural support, transport, signaling.

  • Monomer: Amino acids.

  • Polymer: Polypeptides.

• Nucleic Acids: Store and transmit genetic information.

  • Monomer: Nucleotides.

  • Polymer: DNA and RNA polynucleotides.

• Lipids: Energy storage, membrane structure, signaling (not true polymers).

Polymerization and Hydrolysis

Macromolecules are formed by dehydration synthesis (removal of water) and broken down by hydrolysis (addition of water).

• Dehydration Reaction: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

Protein Structure

Proteins have four levels of structure that determine their function.

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Local folding (alpha-helix, beta-sheet) stabilized by hydrogen bonds.

• Tertiary Structure: 3D folding due to interactions between R groups.

• Quaternary Structure: Association of multiple polypeptide chains.

ATP: The Energy Currency

ATP (adenosine triphosphate) stores and transfers energy within cells via its phosphate groups.

Chapter 4: Cell Structure and Function

Cell Membranes

Cell membranes are composed of a phospholipid bilayer with embedded proteins, providing a semi-permeable barrier.

• Phospholipids: Have hydrophilic heads and hydrophobic tails; self-assemble into bilayers.

• Membrane Proteins: Facilitate transport, signaling, and structural support.

Cell Organelles and Their Functions

Organelles compartmentalize cellular functions in eukaryotic cells.

• Ribosomes: Protein synthesis; can be free (cytosol) or bound (rough ER).

• Vacuoles: Storage and transport; plant cells have large central vacuoles.

• Lysosomes: Contain digestive enzymes to break down macromolecules and waste.

• Peroxisomes: Break down fatty acids and detoxify harmful substances.

• Mitochondria: Site of cellular respiration and ATP production.

• Chloroplasts: Site of photosynthesis in plant cells.

• Nucleus: Contains DNA; site of transcription.

• Endoplasmic Reticulum (ER):

  • Rough ER: Protein synthesis (with ribosomes).

  • Smooth ER: Lipid synthesis, detoxification, Ca2+ storage.

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

• Cytoskeleton: Provides structural support and facilitates movement.

Gene Expression and Protein Transport

Gene expression involves transcription (DNA to RNA) and translation (RNA to protein). Proteins are sorted and transported within the cell.

• Central Dogma: DNA → RNA → Protein.

• Protein Sorting: Proteins synthesized in the rough ER are transported to the Golgi apparatus, then to their final destinations (e.g., cell membrane, lysosome, secretion).

Endosymbiotic Theory

The endosymbiotic theory explains the origin of mitochondria and chloroplasts as formerly free-living prokaryotes that were engulfed by ancestral eukaryotic cells.

• Both organelles have their own DNA and ribosomes.

• They can grow and reproduce independently within the cell.