Biology: The Study of Life

Defining Life and Its Characteristics

Biology is the scientific study of life, encompassing the diversity and unity of living organisms. All living things share fundamental traits that distinguish them from non-living matter.

• Cellular Organization: All organisms are composed of one or more membrane-bound cells.

• Reproduction: Organisms can replicate or reproduce.

• Genetic Information: Hereditary information is encoded in genes.

• Energy Utilization: Organisms acquire and use energy.

• Evolution: Populations of organisms evolve over time.

Cell Theory: All organisms are made of cells, and all cells arise from preexisting cells. This theory is supported by extensive evidence, including experiments by Pasteur that refuted spontaneous generation.

Chromosome Theory of Inheritance: Genetic information is carried on chromosomes, composed of DNA. The central dogma describes the flow of genetic information: DNA → RNA → Protein.

Evolution by Natural Selection: Evolution is the change in heritable characteristics of populations over time. Natural selection occurs when individuals with advantageous traits produce more offspring, leading to adaptation and speciation.

Tree of Life: The evolutionary relationships among species can be depicted as a phylogenetic tree, with three major domains: Bacteria, Archaea, and Eukarya.

Scientific Process: Biologists use hypothesis testing and experimental design to answer questions about the natural world, relying on control groups, repeatability, and careful observation.

Water and Carbon: The Chemical Basis of Life

Atomic Structure and Chemical Bonds

Atoms are the fundamental units of matter, composed of protons, neutrons, and electrons. The arrangement of electrons in shells and orbitals determines how atoms interact to form molecules.

• Covalent Bonds: Atoms share electrons; can be nonpolar (equal sharing) or polar (unequal sharing).

• Ionic Bonds: Electrons are transferred from one atom to another, creating charged ions (cations and anions).

• Molecular Shape: The geometry of molecules is determined by the arrangement of electron orbitals and the types of bonds present.

Properties of Water

• Polarity: Water is a polar molecule, allowing it to form hydrogen bonds.

• Cohesion and Adhesion: Water molecules stick to each other (cohesion) and to other substances (adhesion).

• Surface Tension: Water has a high surface tension due to hydrogen bonding.

• Density: Ice is less dense than liquid water, so it floats.

• High Specific Heat and Heat of Vaporization: Water absorbs and retains heat, moderating temperature changes.

• Solvent Properties: Water dissolves many polar and ionic substances (hydrophilic), but not nonpolar substances (hydrophobic).

Acids, Bases, and pH

• Acids: Donate protons (H+).

• Bases: Accept protons.

• pH Scale: Measures proton concentration:

• Buffers: Compounds that minimize changes in pH, maintaining homeostasis.

Chemical Reactions and Thermodynamics

• First Law of Thermodynamics: Energy is conserved; it can change forms but cannot be created or destroyed.

• Spontaneous Reactions: Occur without added energy if they increase entropy (disorder) or release energy (lower potential energy).

• Entropy: A measure of disorder; increases in spontaneous processes.

Organic Molecules and Functional Groups

• Carbon: Forms the backbone of organic molecules, allowing for structural diversity (chains, rings).

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

• Polymerization: Monomers are joined by condensation (dehydration) reactions and broken by hydrolysis.

Protein Structure and Function

Amino Acids and Peptide Bonds

Proteins are polymers of amino acids, each with a central carbon, amino group, carboxyl group, hydrogen atom, and a unique side chain (R-group).

• Side Chains: Determine the properties (polar, nonpolar, charged) and reactivity of amino acids.

• Peptide Bonds: Link amino acids via condensation reactions, forming polypeptides with directionality (N-terminus to C-terminus).

Levels of Protein Structure

• Primary Structure: The unique sequence of amino acids.

• Secondary Structure: Local folding into α-helices and β-pleated sheets, stabilized by hydrogen bonds.

• Tertiary Structure: Overall 3D shape due to interactions among R-groups (hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bridges, van der Waals forces).

• Quaternary Structure: Association of multiple polypeptide subunits.

Protein Folding and Function

• Folding: Proteins fold spontaneously or with the help of molecular chaperones; correct folding is essential for function.

• Denaturation: Loss of structure (unfolding) leads to loss of function.

• Prions: Misfolded proteins that can cause disease (e.g., mad cow disease).

Functions of ProteinskCatalysis: Enzymes speed up chemical reactions by lowering activation energy; have specific active sites for substrates.

• Structure: Provide support (e.g., collagen, keratin).

• Movement: Motor and contractile proteins enable movement.

• Signaling: Transmit signals within and between cells.

• Transport: Move substances across membranes and within organisms.

• Defense: Antibodies and other proteins protect against disease.

An Introduction to Carbohydrates

Monosaccharides: Structure and Variation

Carbohydrates are organic molecules with the general formula (CH2O)n. Monosaccharides (simple sugars) are the monomers of carbohydrates.

• Functional Groups: Contain a carbonyl group (C=O) and multiple hydroxyl groups (–OH).

• Classification: By number of carbons (triose: 3, pentose: 5, hexose: 6), and by position of carbonyl (aldose: end, ketose: middle).

• Isomerism: Spatial arrangement of –OH groups leads to structural isomers (e.g., glucose vs. galactose).

• Ring Formation: In aqueous solutions, monosaccharides with five or more carbons form rings; the new –OH at the anomeric carbon can be α (below plane) or β (above plane).

Polysaccharides: Structure and Function

• Oligosaccharides: Short chains of monosaccharides.

• Polysaccharides: Long chains; can be storage or structural.

• Glycosidic Linkages: Covalent bonds formed by condensation reactions between –OH groups; can vary in position (e.g., α-1,4 or β-1,4), leading to diversity in structure and function.

Roles of Carbohydrates in Cells

• Structural Support: Cellulose, chitin, and peptidoglycan form strong fibers resistant to degradation, providing rigidity to cell walls.

• Cellular Identity: Oligosaccharides on glycoproteins act as identification badges for cell-cell recognition and signaling.

• Energy Storage: Starch and glycogen store chemical energy; their α-glycosidic linkages are easily hydrolyzed by enzymes (e.g., amylase, phosphorylase) to release glucose for ATP production.

Photosynthesis Equation:

Lipids, Membranes, and the First Cells

Lipid Structure and Types

Lipids are hydrophobic molecules, primarily composed of hydrocarbons. They are not true polymers but are essential for cell structure and function.

• Fatty Acids: Hydrocarbon chains with a carboxyl group; can be saturated (no double bonds) or unsaturated (one or more double bonds, causing kinks).

• Fats (Triglycerides): Glycerol linked to three fatty acids via ester linkages; energy storage.

• Steroids: Four-ring structure with various side groups (e.g., cholesterol).

• Phospholipids: Glycerol, two fatty acids, and a phosphate group; amphipathic (hydrophilic head, hydrophobic tail).

Membrane Structure and Function

• Phospholipid Bilayer: In water, phospholipids spontaneously form bilayers with hydrophobic tails inward and hydrophilic heads outward.

• Selective Permeability: Small nonpolar molecules cross easily; large or charged molecules cross slowly or not at all.

• Membrane Fluidity: Influenced by fatty acid saturation, cholesterol content, and temperature.

Transport Across Membranes

• Diffusion: Movement of molecules from high to low concentration.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Facilitated Diffusion: Channel and carrier proteins allow passive movement of specific molecules.

• Active Transport: Protein pumps use ATP to move substances against their concentration gradient.

• Secondary Active Transport: Uses gradients established by primary active transport to move other substances.

Fluid-Mosaic Model

Biological membranes are composed of a fluid phospholipid bilayer with embedded proteins (integral and peripheral), allowing for dynamic structure and function.

Key Vocabulary

• Monomer, Polymer, Macromolecule

• Condensation (Dehydration) Reaction, Hydrolysis

• Glycosidic Linkage, Peptide Bond, Ester Linkage

• Hydrophilic, Hydrophobic, Amphipathic

• Enzyme, Substrate, Active Site

• Isomer, Anomer, Oligosaccharide, Polysaccharide

• Phospholipid, Steroid, Triglyceride

• Diffusion, Osmosis, Facilitated Diffusion, Active Transport

• Glycoprotein, Cell Wall, Plasma Membrane

Additional info: These notes synthesize and expand upon the provided lecture outlines, learning objectives, and vocabulary lists for foundational chapters in General Biology, focusing on the structure and function of biomolecules, cell theory, and the chemical basis of life. For further study, students should practice drawing molecular structures, predicting the effects of molecular changes, and applying these concepts to biological systems.