Chapter 2: The Chemical Context of Life

Chemical Elements and Compounds

The study of biology begins with understanding the chemical elements and compounds that make up living organisms. Elements are pure substances, while compounds are combinations of elements in fixed ratios.

• Element: A pure substance made of one type of atom (e.g., Na, Au, Cl).

• Compound: A substance with two or more elements in a fixed ratio (e.g., H2O, CO2, NaCl).

• Example: Water (H2O) is a compound made of hydrogen and oxygen.

Exploring Life on Its Many Levels

Most living matter is composed of a few key elements. Understanding their prevalence is essential for studying biological systems.

• Major elements in living matter: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur.

• These elements make up about 96% of living matter.

Atoms and Molecules

Atoms are the basic units of matter, defined by their atomic number, mass number, and valence. Molecules are combinations of atoms bonded together.

• Atomic number: Number of protons in the nucleus.

• Mass number: Sum of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Radioactive isotopes: Unstable isotopes that decay, changing the element and emitting radiation.

• Applications: Used as tracers in metabolism and medical imaging.

Electron Shells and Chemical Bonds

Atoms interact through chemical bonds, which are determined by electron arrangements. The main types are covalent, ionic, and hydrogen bonds.

• Covalent bond: Atoms share electrons (e.g., H2, O2, N2).

• Ionic bond: Electrons are transferred, creating charged ions (e.g., NaCl).

• Polar covalent bond: Electrons are shared unequally due to differences in electronegativity (e.g., H2O).

• Hydrogen bond: Weak attraction between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Van der Waals Interactions

These are weak attractions due to temporary shifts in electron distribution, important for molecular flexibility and biological processes.

• Example: Geckos use van der Waals forces to climb surfaces.

Chapter 3: Carbon and the Molecular Diversity of Life

The Importance of Carbon

Carbon forms the backbone of organic molecules, allowing for a diversity of structures and functions in living organisms.

• Carbon skeletons: Vary in length, branching, arrangement, rings, and chemical reactivity.

• Functional groups: Specific groups of atoms that confer chemical properties (e.g., hydroxyl, carboxyl, amino, phosphate).

Macromolecules: Structure and Function

Biological macromolecules are polymers made from monomers. The four major classes are carbohydrates, proteins, lipids, and nucleic acids.

• Carbohydrates: Sugars and polymers of sugars; provide energy and structural support.

• Proteins: Polymers of amino acids; perform a wide range of functions including catalysis, transport, and defense.

• Lipids: Hydrophobic molecules; important for energy storage and membrane structure.

• Nucleic acids: DNA and RNA; store and transmit genetic information.

Polymer Formation and Breakdown

• Dehydration synthesis: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

• Equation for hydrolysis:

Carbohydrates: Fuel and Building Material

• Monosaccharides: Single sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides linked together (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose).

• Function: Energy storage (starch in plants, glycogen in animals) and structural support (cellulose in plants).

Lipids: Diverse Hydrophobic Molecules

• Fats: Glycerol + fatty acids; energy storage.

• Phospholipids: Major component of cell membranes; amphipathic (hydrophilic head, hydrophobic tails).

• Steroids: Four fused rings; hormones and cholesterol.

Proteins: Many Structures, Many Functions

• Amino acids: Building blocks of proteins; 20 different types.

• Peptide bond: Covalent bond between amino acids.

• Protein structure: Four levels—primary, secondary, tertiary, quaternary.

• Denaturation: Loss of protein structure due to heat, pH, or chemicals.

Nucleic Acids: DNA and RNA

• Nucleotides: Monomers of nucleic acids; consist of a sugar, phosphate group, and nitrogenous base.

• DNA: Double helix; stores genetic information.

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

Chapter 4: A Tour of the Cell

How We Study Cells

Cells are the basic units of life. Their size is limited by the surface area to volume ratio, which affects nutrient uptake and waste removal.

• Microscopy: Used to observe cell structure and function.

• Prokaryotic vs. Eukaryotic cells: Prokaryotes lack a nucleus; eukaryotes have a nucleus and organelles.

The Nucleus and Ribosomes

The nucleus contains genetic material and controls cell activities. Ribosomes are the site of protein synthesis.

• Nucleus: Contains DNA; surrounded by a nuclear envelope.

• Ribosomes: Made of rRNA and protein; synthesize proteins.

Endomembrane System

This system includes organelles that work together to modify, package, and transport lipids and proteins.

• Components: Endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles.

• Function: Synthesis, modification, and transport of biomolecules.

Other Membranous Organelles

• Mitochondria: Site of cellular respiration; produces ATP.

• Chloroplasts: Site of photosynthesis in plants; converts solar energy to chemical energy.

The Cytoskeleton

The cytoskeleton provides structural support, cell movement, and organization.

• Components: Microtubules, microfilaments, intermediate filaments.

• Function: Cell shape, movement, and division.

Cell Surfaces and Junctions

Cells interact with their environment and each other through specialized structures.

• Extracellular matrix: Provides structural support in animal cells.

• Cell junctions: Connect cells and facilitate communication.

• Types: Tight junctions (prevent leakage), gap junctions (communication), desmosomes (anchor cells).

Chapter 5: Membrane Structure and Function

Membrane Structure

Cell membranes are composed of a phospholipid bilayer with embedded proteins, providing selective permeability and fluidity.

• Phospholipids: Have hydrophilic heads and hydrophobic tails; form bilayers in water.

• Fluid mosaic model: Describes the dynamic arrangement of lipids and proteins.

• Selective permeability: Allows certain molecules to pass while blocking others.

Membrane Proteins

• Integral proteins: Span the membrane; involved in transport and signaling.

• Peripheral proteins: Attached to the surface; involved in cell recognition and support.

• Transport proteins: Facilitate movement of substances across the membrane.

Table: Types of Chemical Bonds

Table: Major Macromolecules

Additional info: Some explanations and examples have been expanded for clarity and completeness, including the addition of tables and equations for hydrolysis and membrane structure.