Properties of Life and Atoms

Characteristics of Living Things

All living organisms share fundamental properties that distinguish them from non-living matter.

• Cellular Organization: All living things are composed of one or more cells.

• Metabolism: Living organisms carry out chemical reactions to obtain and use energy.

• Homeostasis: The ability to maintain stable internal conditions.

• Growth and Development: Organisms grow and develop according to specific instructions coded in their DNA.

• Reproduction: Living things reproduce, passing genetic information to offspring.

• Response to Stimuli: Organisms respond to environmental changes.

• Evolution: Populations of organisms evolve over time.

Atomic Structure

Atoms are the basic units of matter, consisting of protons, neutrons, and electrons.

• Nucleus: Contains protons (positive charge) and neutrons (neutral).

• Electron Cloud: Electrons (negative charge) orbit the nucleus in energy levels.

• Atomic Number: Number of protons in the nucleus.

• Mass Number: Sum of protons and neutrons.

Chemical Bonds and Water

Types of Chemical Bonds

Atoms interact to form molecules through different types of chemical bonds.

• Covalent Bonds: Atoms share electron pairs. Can be polar (unequal sharing) or nonpolar (equal sharing).

• Ionic Bonds: Electrons are transferred from one atom to another, creating charged ions that attract each other.

• Hydrogen Bonds: Weak attractions between a hydrogen atom in one molecule and an electronegative atom in another.

Example: Water molecules are held together by polar covalent bonds and interact via hydrogen bonds.

Properties of Water

Water is essential for life due to its unique chemical and physical properties.

• Cohesion and Adhesion: Water molecules stick to each other and to other surfaces.

• High Specific Heat: Water absorbs and retains heat, helping regulate temperature.

• Solvent Abilities: Water dissolves many substances, facilitating chemical reactions.

• Acid-Base Reactions: Water can participate in acid-base chemistry, acting as both an acid and a base.

Acids, Bases, and pH

Acids and bases are substances that alter the concentration of hydrogen ions in a solution.

• Acid: Substance that increases the concentration of ions.

• Base: Substance that decreases the concentration of ions (or increases ).

• pH Scale: Measures acidity or basicity; ranges from 0 (acidic) to 14 (basic), with 7 as neutral.

Organic Molecules and Macromolecules

Carbon and Its Versatility

Carbon atoms form the backbone of organic molecules due to their ability to form four covalent bonds.

• Diversity: Carbon can bond with many elements, creating a variety of structures (chains, rings).

• Functional Groups: Specific groups of atoms (e.g., hydroxyl, carboxyl) confer unique properties.

Macromolecules: Structure and Function

Biological macromolecules include carbohydrates, proteins, lipids, and nucleic acids.

• Carbohydrates: Provide energy and structural support. Monomers are monosaccharides.

• Proteins: Made of amino acids; perform diverse functions including catalysis, transport, and structure.

• Lipids: Include fats, oils, and phospholipids; important for energy storage and membrane structure.

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

Polymerization and Hydrolysis

Macromolecules are assembled and disassembled through specific chemical reactions.

• Dehydration Synthesis: Monomers are joined by removing water.

• Hydrolysis: Polymers are broken down by adding water.

Proteins and Amino Acids

Structure of Proteins

Proteins have complex structures that determine their function.

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Local folding (alpha helices, beta sheets) stabilized by hydrogen bonds.

• Tertiary Structure: Overall 3D shape formed by interactions among side chains.

• Quaternary Structure: Association of multiple polypeptide chains.

Amino Acids and Side Chains

Amino acids differ in their side chains, which affect protein structure and function.

• R Group: The variable side chain that determines the properties of each amino acid.

• Classification: Amino acids can be polar, nonpolar, acidic, or basic.

Protein Folding and Function

Protein folding is critical for biological activity; misfolding can lead to disease.

• Denaturation: Loss of structure due to changes in temperature, pH, or chemicals.

• Chaperones: Proteins that assist in proper folding.

Lipids and Membranes

Types of Lipids

Lipids are hydrophobic molecules with diverse functions.

• Fats: Energy storage; composed of glycerol and fatty acids.

• Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.

• Steroids: Include hormones and cholesterol.

Phospholipid Bilayer Structure

Cell membranes are primarily composed of a phospholipid bilayer.

• Hydrophilic Heads: Face outward toward water.

• Hydrophobic Tails: Face inward, away from water.

• Fluid Mosaic Model: Membranes are dynamic, with proteins and lipids moving within the layer.

Membrane Proteins and Selective Permeability

Membrane proteins facilitate transport and communication.

• Integral Proteins: Span the membrane; involved in transport.

• Peripheral Proteins: Attached to the surface; involved in signaling.

• Selectivity: Membranes allow certain substances to pass while blocking others.

Cellular Transport Mechanisms

Passive and Active Transport

Cells move substances across membranes using different mechanisms.

• Passive Transport: Movement down a concentration gradient; includes diffusion and osmosis.

• Facilitated Diffusion: Uses membrane proteins to help substances cross.

• Active Transport: Requires energy (ATP) to move substances against a gradient.

Example: Sodium-potassium pump uses ATP to transport ions across the membrane.

Endocytosis and Exocytosis

Cells transport large molecules via vesicles.

• Endocytosis: Cell engulfs material by forming a vesicle.

• Exocytosis: Vesicle fuses with membrane to release contents outside the cell.

Cell Structure: Prokaryotes vs. Eukaryotes

Prokaryotic and Eukaryotic Cells

Cells are classified based on the presence or absence of a nucleus and organelles.

Cell Organelles and Functions

Eukaryotic cells contain specialized organelles that perform distinct functions.

• Nucleus: Stores genetic material (DNA).

• Mitochondria: Site of cellular respiration and energy production.

• Endoplasmic Reticulum (ER): Synthesizes proteins and lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins.

• Lysosomes: Digest cellular waste.

• Chloroplasts: (Plants) Site of photosynthesis.

Integration: Organelles work together to maintain cellular activities and homeostasis.