Bio exam 1
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General Biology Knowt Study Guide
1. Chemistry of Life
Water Properties & Molecular Interactions
Water molecules are polar: oxygen is slightly negative, hydrogen slightly positive.
Hydrogen bonds form between water molecules.
Responsible for cohesion (water sticks to water) and adhesion (water sticks to other surfaces).
Explains surface tension.
Water moderates temperature due to high specific heat and heat of vaporization.
Key Water Properties:
Cohesion: Molecules sticking together → important for plant water transport.
Adhesion: Water molecules sticking to other surfaces.
Surface tension: Water resists external force due to hydrogen bonding.
Atomic Structure Basics
Atomic number: Number of protons in an atom.
Mass number: Protons + neutrons.
Electrons determine chemical reactivity.
Cations: Positively charged (lose electrons).
Anions: Negatively charged (gain electrons).
Bond Types:
Bond Type | Strength | Example |
Covalent (sharing electrons) | Strong | H₂O, CH₄ |
Ionic (transfer of electrons) | Moderate | NaCl |
Hydrogen bond | Weak individually but strong collectively | Between water molecules |
pH and Acids/Bases
pH scale: Measures concentration of hydrogen ions (H⁺).
Acidic: pH < 7 (more H⁺)
Basic: pH > 7 (more OH⁻)
Strong acids/bases dissociate completely.
Buffer systems help maintain stable pH in living organisms.
Energy Concepts
Potential energy: Stored energy (e.g., in chemical bonds).
Kinetic energy: Energy of motion.
Endergonic reactions: Require energy input (non-spontaneous).
Exergonic reactions: Release energy (spontaneous).
2. Macromolecules
Four Major Classes:
Class | Monomer | Function |
Proteins | Amino acids | Enzymes, structure, signaling |
Nucleic Acids | Nucleotides | Information storage and transfer |
Carbohydrates | Monosaccharides | Energy and structure |
Lipids | Fatty acids & glycerol | Membranes, hormones, energy storage |
Polymerization:
Dehydration reaction: Builds polymers by removing water.
Hydrolysis reaction: Breaks polymers by adding water.
3. Protein Structure
Amino Acid Basics
Central structure: Amino group, carboxyl group, hydrogen, and R group.
R group determines polarity:
Polar: Contains O or N, can form hydrogen bonds.
Nonpolar: Mostly C and H.
Charged: Acidic (-) or Basic (+).
Levels of Protein Structure
Level | Description | Key Bonds |
Primary | Linear sequence of amino acids | Peptide bonds |
Secondary | Local folding (α-helices, β-sheets) | Hydrogen bonds |
Tertiary | 3D shape formed by R group interactions | Ionic, hydrogen, hydrophobic, disulfide bridges |
Quaternary | Multiple polypeptide chains | Same as tertiary |
Protein Denaturation:
Heat, pH, or chemical changes disrupt weak bonds → protein unfolds and loses function.
4. Nucleic Acids
DNA vs RNA
Feature | DNA | RNA |
Sugar | Deoxyribose | Ribose |
Bases | A, T, C, G | A, U, C, G |
Structure | Double helix | Single-stranded |
Function | Genetic storage | Protein synthesis, catalysis |
Base Pairing Rules (Complementary):
A ↔ T (2 hydrogen bonds)
C ↔ G (3 hydrogen bonds)
DNA strands are antiparallel (5’ to 3’ opposite directions).
Chargaff’s Rule:
%A = %T and %C = %G in DNA.
If A = 20%, then T = 20%, C = 30%, G = 30%.
5. Membrane Structure & Function
Phospholipid Bilayer
Phospholipids:
Hydrophilic heads face outward (towards water).
Hydrophobic tails face inward (away from water).
Self-assemble spontaneously in water → selectively permeable membrane.
Membrane Fluidity Factors:
Unsaturated fatty acids: Increase fluidity (kinked tails).
Saturated fatty acids: Decrease fluidity.
Cholesterol:
Prevents solidification at low temperatures.
Prevents over-fluidity at high temperatures.
Types of Transport Across Membranes
Type | Energy Required? | Example |
Simple diffusion | No | O₂, CO₂ |
Osmosis | No | Water |
Facilitated diffusion | No | Glucose via transport protein |
Active transport | Yes (ATP) | Sodium-potassium pump |
Secondary active transport | Indirect energy | Sodium-glucose cotransporter |
Osmosis & Tonicity
Hypotonic: Water moves into cell → cell swells.
Isotonic: No net water movement → cell stays same size.
Hypertonic: Water moves out of cell → cell shrinks.
Trick: Water always moves toward the area with higher solute concentration.
6. Predicting Molecule Movement
If solute is permeable: It moves down its concentration gradient.
If solute is not permeable: Water moves instead to balance concentrations.
Example:
Inside cell: 1.5 M solute
Outside cell: 0.5 M solute
Water moves into the cell (hypotonic environment).
7. Lipids and Membrane Permeability
Permeability Ranking:
High: Small nonpolar molecules (O₂, CO₂)
Moderate: Small uncharged polar molecules (H₂O)
Low: Large uncharged polar molecules (glucose)
Very Low: Ions (Na⁺, Cl⁻)
8. Experimental Applications
Examples:
Increasing cholesterol → stabilizes membrane over temperature changes.
Cold environment → increase unsaturated fatty acids to keep fluidity.
Hot environment → increase saturated fatty acids to reduce excess fluidity.
9. Key Terms for Flashcards
Cohesion, adhesion, surface tension
Hydrogen bond, ionic bond, covalent bond
Isotonic, hypertonic, hypotonic
Endergonic, exergonic
Phospholipid bilayer
Primary vs secondary vs tertiary vs quaternary structure
Base pairing rules
Chargaff’s rule
Facilitated diffusion, active transport