General Biology: Introduction to Biological Organization, Chemistry of Life, and Macromolecules

Levels of Biological Organization

From Populations to the Biosphere

Biological systems are organized in a hierarchy, from the smallest units to the largest, encompassing all life on Earth.

• Population: A group of individuals of the same species living in a specific area.

• Community: All populations of different species living and interacting in an area.

• Ecosystem: The community plus the non-living (abiotic) environment.

• Biosphere: The sum of all ecosystems; all life on Earth.

Cell Structure and Diversity

Prokaryotic vs. Eukaryotic Cells

Cells are the basic unit of structure and function in living organisms. They are classified into two main types:

• Prokaryotic cells: Lack a nucleus and membrane-bound organelles (e.g., Bacteria and Archaea).

• Eukaryotic cells: Have a nucleus and membrane-bound organelles (e.g., Plants, Animals, Fungi, Protists).

All cells share certain characteristics, such as being enclosed by a membrane.

Emergent Properties and Reductionism

Complexity in Biological Systems

Emergent properties arise from the arrangement and interaction of parts within a system, leading to new characteristics at each level of organization. Reductionism is the approach of reducing complex systems to simpler components for study.

Energy and Life

Energy Transfer and Transformation

Life requires the transfer and transformation of energy and matter. Organisms use energy to perform biological work, and energy flows through ecosystems while nutrients cycle.

• Producers: Organisms (like plants) that convert solar energy into chemical energy via photosynthesis.

• Consumers: Organisms that obtain energy by eating other organisms.

Genetics and Information Flow

DNA and Genes

Genetic information is encoded in DNA, which is the universal genetic language common to all organisms. Genes are units of inheritance that transmit information from parents to offspring.

• Three domains of life: Bacteria, Archaea, Eukarya

• Inherited DNA directs the development of an organism.

Chemistry of Life

Elements, Atoms, and Compounds

Matter is made up of elements, which are substances that cannot be broken down by chemical means. Compounds are substances consisting of two or more elements in fixed ratios.

• Essential elements: About 25 elements are essential for life; the most abundant are carbon, hydrogen, nitrogen, and oxygen (the "Big 4").

• Atoms: The smallest unit of matter that retains the properties of an element.

• Subatomic particles: Protons (positive), neutrons (neutral), electrons (negative).

• Atomic number: Number of protons in an atom.

• Mass number: Number of protons plus neutrons.

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

Table: Properties of Subatomic Particles

Particle	Charge	Location
Proton	+1	Nucleus
Neutron	0	Nucleus
Electron	-1	Electron cloud

Chemical Bonds and Interactions

Types of Bonds

• Covalent bonds: Sharing of a pair of valence electrons between two atoms.

• Non-polar covalent bond: Electrons shared equally.

• Polar covalent bond: Electrons shared unequally, creating partial charges.

• Ionic bonds: Transfer of electrons from one atom to another, resulting in charged ions.

• Hydrogen bonds: Weak bonds between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

• Van der Waals interactions: Weak attractions due to transient local partial charges.

Valence and Bonding Capacity

• Valence electrons: Electrons in the outermost shell.

• Noble gases: Atoms with complete valence shells; generally unreactive.

• Bonding capacity (valence): Number of bonds an atom can form.

Element	Number of Covalent Bonds
H	1
O	2
N	3
C	4

Water and Its Properties

Hydrogen Bonding and Water's Unique Features

• Cohesion: Water molecules stick together via hydrogen bonds.

• Adhesion: Water molecules stick to other substances.

• Surface tension: Difficulty of breaking the surface of a liquid due to cohesive forces.

• High specific heat: Water resists temperature change.

• Expansion upon freezing: Ice is less dense than liquid water.

• Versatility as a solvent: Water dissolves many substances due to its polarity.

• Hydrophobic: Substances that do not interact with water (e.g., oils).

• Hydrophilic: Substances that interact with water.

Organic Chemistry and Macromolecules

Carbon-Based Life and Organic Compounds

Life on Earth is carbon-based. Organic compounds contain carbon and are the basis for macromolecules such as carbohydrates, proteins, nucleic acids, and lipids.

• Functional groups: Groups of atoms that affect molecular function by being directly involved in chemical reactions (e.g., carboxyl, hydroxyl, carbonyl, etc.).

• ATP (adenosine triphosphate): The cell's source of energy.

Macromolecules: Structure and Function

Dehydration and Hydrolysis Reactions

• Dehydration reaction: Two monomers bond together through the loss of a water molecule.

• Hydrolysis: Polymers are disassembled to monomers by the addition of water.

Enzymes

• Enzymes: Biological catalysts that speed up or facilitate chemical reactions.

Carbohydrates

Carbohydrates serve as fuel and building material. They include sugars and their polymers.

• Monosaccharides: Simple sugars (e.g., glucose, fructose); molecular formulas are multiples of CH2O.

• Disaccharides: Formed when a dehydration reaction joins two monosaccharides (e.g., sucrose, lactose).

• Polysaccharides: Polymers of sugars, with storage and structural roles.

Polysaccharide	Function	Location
Starch	Storage	Plants
Glycogen	Storage	Animals (muscle, liver)
Cellulose	Structural	Plant cell walls
Chitin	Structural	Fungi cell walls, arthropod exoskeletons

Lipids

Lipids are hydrophobic molecules, consisting mostly of hydrocarbons. They include fats, phospholipids, and steroids.

1. Triglycerides (fats): Formed by glycerol and three fatty acids.

   • Saturated fatty acids: No double bonds; solid at room temperature.

   • Unsaturated fatty acids: One or more double bonds; liquid at room temperature.

   • Hydrogenation: Converts unsaturated fats to saturated fats by adding hydrogen.

2. Phospholipids: Major constituents of cell membranes; have hydrophilic heads and hydrophobic tails. In water, they form bilayers.

3. Steroids: Characterized by a carbon skeleton with four fused rings.

   • Cholesterol: Important component of animal cell membranes.

   • Sex hormones: Estradiol and testosterone.

Additional info:

• Proteins and nucleic acids are also major classes of macromolecules, but detailed coverage is not included in these notes.