Chemistry and Biology: The Foundation of Life

Relationship Between Biology and Chemistry

Biology and chemistry are closely linked because all living things are composed of matter, which is governed by chemical principles. Understanding the chemical basis of life is essential for studying biological processes.

• Matter: Anything that has mass and occupies space. All living and non-living things are made of matter.

• Law of Conservation of Matter: Matter cannot be created or destroyed, only transformed.

States of Matter

Phases of Matter

Matter exists in three main phases relevant to biology: solid, liquid, and gas. Plasma is a fourth phase but is not found in living organisms.

• Solid: Particles are tightly packed and vibrate in place.

• Liquid: Particles are less tightly packed and can move past each other.

• Gas: Particles are far apart and move freely.

Atoms and Elements

Structure of the Atom

The atom is the smallest unit of an element that retains its chemical properties. The arrangement of subatomic particles determines the atom's behavior and the state of matter.

• Nucleus: Contains protons (positive charge) and neutrons (no charge).

• Electron Cloud: Region where electrons (negative charge) are likely to be found, orbiting the nucleus.

Elements

An element is a pure substance that cannot be broken down into other substances by chemical means. Each element is defined by its number of protons.

• Examples: Oxygen (O), Silver (Ag), Copper (Cu)

• Four elements make up 96% of living matter: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N)

• Other important elements: Phosphorus (P), Sulfur (S)

• Trace elements are required in small amounts (e.g., Iodine, Fluoride)

Classification of Elements

• Metals, Nonmetals, and Metalloids

Subatomic Particles

• Proton: Positively charged, found in the nucleus

• Neutron: No charge, found in the nucleus

• Electron: Negatively charged, orbits the nucleus

Atomic Number and Mass

• Atomic Number: Number of protons in an atom

• Atomic Mass: Number of protons plus neutrons

Electron Shells and Valence Electrons

Electrons occupy energy levels or shells around the nucleus. The outermost shell contains valence electrons, which determine chemical reactivity.

• 1st shell: up to 2 electrons

• 2nd shell: up to 8 electrons

• 3rd shell: up to 18 electrons

• Octet Rule: Atoms are most stable with 8 electrons in their outer shell (except H and He, which are stable with 2)

Isotopes and Ions

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons. Some isotopes are stable, while others are radioactive.

• Example: Carbon-12, Carbon-13, Carbon-14

• Radioactive isotopes can decay, emitting radiation (used in medicine, but can be dangerous in large amounts)

Ions

Ions are atoms that have gained or lost electrons, resulting in a net charge.

• Cation: Positive ion (lost electrons)

• Anion: Negative ion (gained electrons)

Chemical Bonds

Ionic Bonds

Ionic bonds form when electrons are transferred from one atom to another, creating oppositely charged ions that attract each other. Usually occurs between metals and nonmetals.

• Example: Sodium chloride (NaCl)

Covalent Bonds

Covalent bonds form when two atoms share electrons. These are strong bonds, typically between nonmetals.

• Polar Covalent Bond: Electrons are shared unequally, creating partial charges (e.g., water)

• Nonpolar Covalent Bond: Electrons are shared equally

Hydrogen Bonds

Hydrogen bonds are weak attractions between a hydrogen atom in one molecule and an electronegative atom (like oxygen or nitrogen) in another molecule. Many hydrogen bonds together can be strong.

Water: Structure and Properties

Structure of Water

Water (H2O) is a polar molecule, with oxygen having a partial negative charge and hydrogen having a partial positive charge. This polarity allows water molecules to form hydrogen bonds with each other.

Properties of Water

• Cohesion: Water molecules stick to each other due to hydrogen bonding (e.g., water droplets)

• Adhesion: Water molecules stick to other substances (e.g., water climbing up plant vessels)

• Capillary Action: Combination of cohesion and adhesion allows water to move up thin tubes, essential for plant transport

• Surface Tension: Water has a strong surface tension, allowing small objects to float

• High Specific Heat: Water can absorb a lot of heat before changing temperature, helping regulate climate and body temperature

• High Heat of Vaporization: It takes a lot of energy to convert water from liquid to gas, important for cooling mechanisms like sweating

• Density of Ice: Ice is less dense than liquid water, so it floats, insulating aquatic life in winter

• Solvent Properties: Water dissolves many ionic and polar substances, making it an excellent medium for biological reactions

Macromolecules: The Molecules of Life

The Chemistry of Carbon

Carbon is the backbone of organic molecules due to its ability to form four covalent bonds, allowing for a variety of structures (chains, rings, branching).

• Organic Compounds: Contain carbon and are found in living things

• Inorganic Compounds: Do not contain carbon-hydrogen bonds

Types of Biological Macromolecules

• Carbohydrates: Sugars and starches, provide energy and structural support

• Lipids: Fats, oils, and waxes, store energy, make up membranes, and act as signaling molecules

• Proteins: Made of amino acids, perform most cellular functions

• Nucleic Acids: DNA and RNA, store and transmit genetic information

Monomers and Polymers

• Monomer: Small building block molecule

• Polymer: Large molecule made of repeating monomers

• Dehydration Synthesis: Joins monomers by removing water

• Hydrolysis: Breaks polymers into monomers by adding water

Carbohydrates

• Monomer: Monosaccharide (e.g., glucose, fructose)

• Polymer: Polysaccharide (e.g., starch, glycogen, cellulose)

• Functions: Quick energy, energy storage, structural support (cell walls in plants)

Lipids

• Monomer: Fatty acids and glycerol

• Polymer: Triglycerides, phospholipids, steroids

• Functions: Energy storage, cell membrane structure, insulation, signaling

• Saturated Fats: No double bonds, solid at room temperature

• Unsaturated Fats: One or more double bonds, liquid at room temperature

Proteins

• Monomer: Amino acid (20 types)

• Polymer: Polypeptide chain

• Functions: Enzymes, structural support, transport, signaling

• Shape Determines Function: Protein function depends on its three-dimensional shape

Nucleic Acids

• Monomer: Nucleotide (phosphate, sugar, base)

• Polymer: DNA (double helix), RNA (single strand)

• Functions: Store and transmit genetic information

Enzymes and Chemical Reactions

Chemical Reactions

Chemical reactions involve the transformation of reactants into products, often with changes in energy.

• Activation Energy: The energy required to start a reaction

• Enzymes: Proteins that act as catalysts, lowering activation energy and speeding up reactions

How Enzymes Work

• Substrate: The molecule acted upon by the enzyme

• Active Site: The region on the enzyme where the substrate binds

• Specificity: Each enzyme only works with specific substrates (lock and key model)

• Denaturation: Loss of enzyme shape (and function) due to heat, pH, or toxins

Nutrition and Macromolecules in Food

Carbohydrates in Nutrition

• Monosaccharides: Simple sugars, quick energy (e.g., glucose in fruits, candy)

• Polysaccharides: Complex sugars, long-term energy (e.g., starch in bread, pasta)

• Cellulose: Dietary fiber, not digestible by humans but important for digestive health

• Lactose Intolerance: Inability to digest lactose due to lack of lactase enzyme

Lipids in Nutrition

• Unsaturated Fats: Healthier, found in fish, nuts, plant oils

• Saturated Fats: Less healthy, found in meats, butter, dairy

• Trans Fats: Unhealthy, artificially produced

• Essential Fatty Acids: Must be obtained from diet (e.g., omega-3, omega-6)

• Cholesterol: LDL (bad), HDL (good)

Proteins in Nutrition

• Essential Amino Acids: Must be obtained from diet (animal proteins are complete, some plant combinations are complete)

• Protein Allergies: Immune response to specific proteins in food

Nucleic Acids in Nutrition

• Present in all foods of biological origin, but not a significant energy source

Summary Table: Macromolecules

Key Equations and Concepts

• Atomic Mass:

• Chemical Equation Example:

• Dehydration Synthesis:

• Hydrolysis: