General Biology Study Notes: Water, Macromolecules, and Cell Structure

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Chapter 3: Properties of Water

Structure of Water Molecules

The water molecule (H2O) consists of one oxygen atom covalently bonded to two hydrogen atoms. Its unique structure leads to important chemical and physical properties essential for life.

Bonding: Water molecules are arranged in a bent (V) shape, with two partially negative hydrogen atoms bonded to a partially negative oxygen atom.
Polarity: The unequal sharing of electrons causes the oxygen atom to have a partial negative charge and the hydrogen atoms to have a partial positive charge.
Dipole Moment: Water is a polar molecule, meaning it has an unequal distribution of electrons, resulting in a bent shape.
Hydrogen Bonding: A hydrogen bond forms between water and other polar charged molecules.
Example: Water molecules interact with sodium ions (Na+) due to their polarity.

Properties of Water

Water exhibits several unique properties due to its molecular structure and hydrogen bonding.

Cohesion: Water molecules stick to each other due to hydrogen bonds.
Adhesion: Water molecules are attracted to other substances.
Surface Tension: Cohesive forces at the surface create a 'skin' on water.
Capillary Action: Water moves up narrow tubes against gravity due to cohesion and adhesion.
High Specific Heat: Water requires a large amount of energy to change temperature, helping regulate temperatures in living organisms.
High Heat of Vaporization: Water absorbs excess heat when evaporating, cooling organisms and environments.
Density: Liquid water is denser than solid water (ice), which floats due to hydrogen bonding creating an open lattice structure.
Solvent Properties: Water dissolves many substances due to its polarity, breaking ionic and polar bonds (hydration shell).
Example: Water dissolves table salt (NaCl) by surrounding ions with hydration shells.

Chapter 4: Macromolecules

Types of Macromolecules

Macromolecules are large biological molecules essential for cell structure and function. The four major classes are proteins, carbohydrates, lipids, and nucleic acids.

Monomer: A small molecule that can be bonded to other identical molecules to form a polymer.
Polymer: A large molecule made of many monomers joined together.
Condensation (Dehydration) Reaction: Joins two monomers, releasing water.
Hydrolysis Reaction: Breaks polymers into monomers by adding water.
Example: Glucose monomers join to form starch via condensation; starch breaks down to glucose via hydrolysis.

Macromolecule Comparison Table

Macromolecule	Monomer	Function	Example
Carbohydrates	Monosaccharide	Energy storage, structure	Glucose, starch, cellulose
Proteins	Amino acid	Enzymes, structure, movement	Hemoglobin, enzymes
Lipids	Fatty acid, glycerol	Energy storage, membranes	Fats, oils, steroids
Nucleic acids	Nucleotide	Genetic information	DNA, RNA

Chapter 6: Cell Structure and Function

Cell Types

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

Prokaryotic Cells: Lack a nucleus and membrane-bound organelles. DNA is found in the nucleoid region. Example: Bacteria.
Eukaryotic Cells: Have a nucleus and membrane-bound organelles. More complex. Examples: Animals, plants, fungi, protists.
Plant Cells: Eukaryotic cells with cell walls, chloroplasts, and large central vacuoles.
Animal Cells: Eukaryotic cells without cell walls or chloroplasts.
Example: Escherichia coli is a prokaryote; Arabidopsis thaliana is a eukaryote.

Cell Organelles and Their Functions

Organelles are specialized structures within cells that perform specific functions.

Nucleus: Contains DNA, controls cell activities.
Nucleolus: Produces ribosomes.
Chromosomes: DNA and associated proteins; carry genetic information.
Ribosomes: Synthesize proteins; found free in cytoplasm or attached to rough ER.
Endomembrane System: Includes ER, Golgi apparatus, vesicles; involved in transport and processing.
Rough ER (RER): Studded with ribosomes; synthesizes proteins for export.
Smooth ER (SER): Detoxifies chemicals, produces lipids.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for transport.
Lysosomes: Contain digestive enzymes; break down waste.
Vacuoles: Store substances; plant cells have large central vacuoles for water and nutrients.
Mitochondria: Produce ATP via cellular respiration.
Chloroplasts: Site of photosynthesis in plant cells.
Peroxisomes: Break down fatty acids, neutralize toxins.
Cytoskeleton: Provides structure, movement; includes microtubules and filaments.
Cell Wall: Provides support in plant cells.
Extracellular Matrix: Network of proteins supporting animal cells.
Cell Junctions: Connect cells, allow communication.
Example: Muscle cells have many mitochondria for energy; plant cells have chloroplasts for photosynthesis.

Cell Organelle Comparison Table

Organelle	Function	Present in
Nucleus	Stores genetic material	Eukaryotes
Ribosome	Protein synthesis	All cells
Chloroplast	Photosynthesis	Plant cells
Mitochondria	ATP production	Eukaryotes
Cell Wall	Support and protection	Plants, fungi, some prokaryotes

Key Equations and Concepts

Hydrogen Bonding: Weak attraction between a hydrogen atom and an electronegative atom (e.g., oxygen).
Dehydration Synthesis:
Hydrolysis:

Additional info: Some explanations and examples have been expanded for clarity and completeness.