Atoms and Chemical Bonding

Atomic Structure and Subatomic Particles

Atoms are the fundamental units of matter, composed of three main subatomic particles: protons, neutrons, and electrons.

• Proton: Positively charged particle found in the nucleus.

• Neutron: Neutral particle found in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

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

• Ion: Atom or molecule with a net electric charge due to loss or gain of electrons.

• Cation: Positively charged ion (loss of electrons).

• Anion: Negatively charged ion (gain of electrons).

• Valence electrons: Electrons in the outermost shell, important for chemical bonding.

Chemical Bonds:

• Covalent Bonds: Atoms share electrons; strong and common in biological molecules.

• Ionic Bonds: Atoms transfer electrons, creating charged ions that attract each other.

Stability: Atoms are most stable when their valence shell is full, often achieved through bonding.

Example: Sodium (Na) loses an electron to become Na+ (cation), while chlorine (Cl) gains an electron to become Cl- (anion), forming NaCl via ionic bonding.

Water: The Molecule of Life

Properties and Importance of Water

Water's unique properties are essential for life, largely due to its polarity and ability to form hydrogen bonds.

• Cohesion: Water molecules stick to each other due to hydrogen bonding.

• Adhesion: Water molecules stick to other substances.

• Surface tension: The surface of water resists external force due to cohesive forces.

• High specific heat: Water absorbs and retains heat, stabilizing temperatures.

• Excellent solvent: Water dissolves many ionic and polar substances.

• Polarity: Oxygen is more electronegative, giving water a partial negative charge near oxygen and partial positive near hydrogen.

Example: Water dissolves table salt (NaCl) by surrounding Na+ and Cl- ions, separating them.

Carbon and Organic Molecules

Chemical Versatility of Carbon

Carbon is the backbone of biological molecules due to its ability to form four covalent bonds, resulting in diverse structures.

• Forms chains, branches, and rings.

• Enables the creation of large, complex molecules.

Example: Glucose (C6H12O6) forms a ring structure, while fatty acids form long chains.

Functional Groups

Structure and Function of Key Functional Groups

Functional groups are specific groups of atoms within molecules that confer distinct chemical properties.

• Hydroxyl (-OH): Found in alcohols; makes molecules polar.

• Carbonyl (C=O): Found in sugars; increases reactivity.

• Carboxyl (-COOH): Acts as an acid; found in amino acids and fatty acids.

• Amino (-NH2): Acts as a base; found in amino acids.

• Sulfhydryl (-SH): Forms disulfide bridges; stabilizes protein structure.

• Phosphate (-PO4): Involved in energy transfer (e.g., ATP).

• Methyl (-CH3): Affects gene expression and molecular shape.

Special Note: Sulfhydryl groups are crucial for protein structure, forming disulfide bridges that stabilize tertiary and quaternary structures.

Isomers

Structural Isomers and Biological Function

Isomers are molecules with the same molecular formula but different structures, leading to different properties.

• Structural isomers: Differ in the arrangement of atoms.

Example: Glucose and fructose both have the formula C6H12O6 but different structures and functions.

Dehydration Reactions and Hydrolysis

Building and Breaking Macromolecules

Biological macromolecules are assembled and disassembled through dehydration and hydrolysis reactions.

• Dehydration reaction: Removes water to join monomers into polymers.

• Hydrolysis: Adds water to break polymers into monomers.

Example: During digestion, hydrolysis breaks down starch into glucose monomers.

Carbohydrates

Structure, Types, and Functions

Carbohydrates are organic molecules that provide energy and structural support.

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

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

• Glycosidic linkages: Covalent bonds connecting monosaccharides.

Examples:

• Starch: Energy storage in plants.

• Glycogen: Energy storage in animals.

• Cellulose: Structural support in plant cell walls.

• Chitin: Structural support in fungi and arthropods.

Lipids

Types, Structure, and Biological Roles

Lipids are hydrophobic molecules important for energy storage, insulation, hormones, and cell membranes.

• Fats and oils: Energy storage; fats are solid, oils are liquid at room temperature.

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

• Steroids: Hormones and membrane components (e.g., cholesterol).

Saturated fatty acids: No double bonds; straight chains; usually solid.

Unsaturated fatty acids: One or more double bonds; bent chains; usually liquid.

Example: Olive oil contains unsaturated fats, while butter contains saturated fats.

Proteins

Structure, Function, and Denaturation

Proteins are versatile macromolecules with diverse functions, built from amino acids joined by peptide bonds.

• Functions: Enzymes, structure, transport, signaling, movement, defense.

• Primary structure: Amino acid sequence.

• Secondary structure: Alpha helices and beta sheets (hydrogen bonding).

• Tertiary structure: Overall 3D shape (interactions among side chains).

• Quaternary structure: Multiple polypeptide chains together.

• Denaturation: Loss of structure and function due to temperature, pH, or chemicals.

Example: Hemoglobin (quaternary structure) transports oxygen in blood.

Nucleic Acids

Structure and Function

Nucleic acids store and transmit genetic information. DNA and RNA are polymers of nucleotides.

• Nucleotide components: Sugar, phosphate group, nitrogenous base.

• DNA: Stores genetic information; double helix structure.

• RNA: Involved in protein synthesis and gene regulation.

Example: DNA encodes instructions for building proteins essential for life.

Macromolecule Summary Table

Key Diagrams and Concepts to Review

• Water molecules and polarity

• Covalent vs. ionic bonding

• Functional groups

• Amino acid structure

• Fatty acids and phospholipids

• Glucose and fructose as isomers

• Dehydration and hydrolysis reactions

Final Study Checklist

• Why is carbon the backbone of life?

• Why is water considered the molecule of life?

• What is the difference between covalent and ionic bonds?

• How do dehydration reactions differ from hydrolysis?

• What are the major functions of carbohydrates, lipids, proteins, and nucleic acids?

• What functional groups are found in amino acids?

• Why do proteins lose function when denatured?

• Why doesn't the lipid category form true polymers?

Additional info: Students should be able to explain and apply these concepts, as well as identify key molecular structures and reactions relevant to biological macromolecules.