Introduction to Biology

The Study of Life

• Biology is the scientific study of life, aiming to understand the natural world through observation and experimentation.

• Life is organized in a hierarchy: atoms → molecules → macromolecules → organelles → cells → tissues → organs → populations → communities → ecosystems → biosphere.

• The cell is the smallest unit of structure and function in organisms.

• All cells are enclosed by a membrane and share basic characteristics.

• There are two main cell types: prokaryotic (smaller, simpler, no nucleus) and eukaryotic (larger, complex, with nucleus).

• Major differences between plant and animal cells include the presence of a cell wall, chloroplasts (for photosynthesis), and a large central vacuole in plant cells.

Scientific Approaches

• Reductionism: Understanding complex systems by breaking them down into simpler components.

• Emergent properties: New characteristics that arise from the arrangement and interaction of parts within a system.

• Structure defines function: The shape and arrangement of biological structures determine their roles (e.g., the beak of a hummingbird is adapted for feeding on nectar).

Energy and Evolution

• Energy is the capacity to do work; life requires the transfer and transformation of energy and matter (energy flows one way through ecosystems).

• Evolution is the process by which organisms accumulate differences from their ancestors, explaining both the unity and diversity of life.

• There are three domains of life: Bacteria, Archaea, and Eukarya.

Genetic Information

• Life processes involve the expression and transmission of genetic information.

• DNA is the universal genetic material, composed of genes that transmit information from parents to offspring and direct development.

Chemistry of Life

Elements and Atoms

• Matter is anything that takes up space and has mass; it is made up of elements.

• An element is a substance that cannot be broken down by chemical reactions.

• A compound consists of two or more elements in a fixed ratio and has emergent properties distinct from its elements.

• The four most abundant elements in living organisms are hydrogen, carbon, nitrogen, and oxygen (the "Big 4").

• There are 94 natural elements; about 25% are essential for life.

• An atom is the smallest unit of an element, composed of subatomic particles: protons, neutrons, and electrons.

• Atomic number = number of protons.

• Mass number = number of protons + number of neutrons.

• Atomic mass is approximately equal to the mass number.

• Isotopes are atoms of the same element with different numbers of neutrons.

Electron Configuration and Chemical Bonds

• The reactivity of an atom depends on unpaired electrons in the valence shell.

• Valence electrons occupy the outermost shell; atoms with full valence shells are inert (nonreactive).

• Bonding capacity (valence) is the number of bonds an atom can form.

Types of Chemical Bonds

• Covalent bonds: Sharing of electron pairs between atoms; strongest type of bond.

• Non-polar covalent bond: Electrons are shared equally.

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

• Ionic bonds: Attraction between oppositely charged ions (formed when electrons are transferred).

• Hydrogen bonds: Weak attractions between a hydrogen atom covalently bonded to one electronegative atom and another electronegative atom (often oxygen or nitrogen).

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

Water and Its Properties

Structure and Hydrogen Bonding

• Each water molecule can form up to four hydrogen bonds.

Properties of Water

• Cohesive behavior: Water molecules stick together, resulting in surface tension.

• Ability to moderate temperature: Water absorbs and releases heat slowly, stabilizing temperatures.

• Expansion upon freezing: Ice is less dense than liquid water because hydrogen bonds are stable in ice, causing it to float.

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

• Hydrophobic substances (e.g., oil) do not interact with water.

Biomolecules

Organic Molecules and Functional Groups

• Life on Earth is carbon-based; organic compounds contain carbon.

• Major elements and their valencies:

  • H = 1

  • O = 2

  • N = 3

  • C = 4

• Functional groups (e.g., carboxyl, hydroxyl, carbonyl) are chemical groups that affect molecular function by participating in chemical reactions.

• ATP is the cell's main energy currency.

Macromolecules

• Macromolecules include carbohydrates, proteins, and nucleic acids.

• Lipids are not true polymers but are important biological molecules.

• Polymers are long molecules made of repeating units called monomers.

• Dehydration reaction: Joins two monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

• Enzymes speed up chemical reactions.

Carbohydrates

• Serve as fuel and building material.

• Monosaccharides: Simple sugars (e.g., triose, pentose, hexose) with the formula (CH2O)n.

• Disaccharides: Two monosaccharides joined by a glycosidic linkage (dehydration reaction).

• Polysaccharides: Polymers of sugars with storage or structural roles.

• Starch: Storage polysaccharide in plants (glucose monomers).

• Glycogen: Storage polysaccharide in animals (liver and muscle cells).

• Cellulose: Structural polysaccharide in plant cell walls.

• Chitin: Structural polysaccharide in fungal cell walls and arthropod exoskeletons.

• Enzymes that digest starch (alpha linkages) cannot digest cellulose (beta linkages).

Lipids

• Hydrophobic molecules, mainly hydrocarbons.

• Triglycerides (fats): Composed of glycerol and three fatty acids.

• Saturated fats: No double bonds; maximum hydrogen atoms; solid at room temperature.

• Unsaturated fats: One or more double bonds (C=C); bent structure; liquid at room temperature.

• Hydrogenation: Converts some C=C bonds to trans configuration, producing trans fats.

• Phospholipids: Major component of cell membranes; hydrophilic head and hydrophobic tails; form bilayers in water.

• Steroids: Four fused carbon rings (e.g., cholesterol, sex hormones like estradiol and testosterone).

Proteins

• Composed of one or more polypeptides (chains of amino acids linked by peptide bonds).

• Functions: enzymatic, defensive, storage, transport, hormonal, receptor, contractile, and structural.

• Amino acids: Central carbon bonded to amino group, carboxyl group, hydrogen, and R group (side chain).

• Amino acids are classified by R group properties: hydrophobic (non-polar), hydrophilic (polar or charged).

• Protein structure has four levels:

  • Primary: Sequence of amino acids.

  • Secondary: Coils and folds (e.g., alpha helix, beta sheet).

  • Tertiary: Interactions among side chains (R groups).

  • Quaternary: Association of multiple polypeptide chains.

• Sickle-cell disease: Caused by a single amino acid substitution in hemoglobin.

• Protein structure can be altered by changes in pH, salt concentration, or temperature (denaturation).

Nucleic Acids

• Store, transmit, and express hereditary information.

• Gene: Unit of inheritance, made of DNA, that programs amino acid sequence of polypeptides.

• Nucleic acids are polymers (polynucleotides) made of nucleotide monomers.

• Nucleotide: Consists of a nitrogenous base, a pentose sugar, and one or more phosphate groups.

• Two types:

  • DNA (deoxyribonucleic acid): Double helix, two antiparallel strands (5' to 3' directions).

  • RNA (ribonucleic acid): Usually single-stranded.

Table: Comparison of Major Macromolecules

Key Equations and Concepts

• Atomic number:

• Mass number:

• Dehydration reaction (general):

• Hydrolysis (general):