Chemistry and Biology: The Foundation of Life

Biology & Chemistry Connection

Biology and chemistry are deeply interconnected, as 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 nonliving things are made of matter, which cannot be created or destroyed.

• Matter exists in three main phases: solid, liquid, and gas.

There is a fourth phase called plasma, but it is not found in living things.

Atoms and Elements

Structure of the Atom

An atom is the smallest unit of an element that retains its chemical properties. The arrangement of atoms determines the state of matter (solid, liquid, or gas).

• Nucleus: Center of the atom, composed of protons and neutrons.

• Electron cloud: Region where electrons are likely to be found, orbiting the nucleus.

Subatomic Particles

• Proton: Positively charged particle found in the nucleus.

• Neutron: Neutral particle found in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

Elements and Trace Elements

An element is a pure substance that cannot be broken down into other substances. Four elements make up 96% of living matter: carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). Trace elements such as sulfur (S) and phosphorus (P) are vital to life but needed in smaller amounts.

• Mnemonic: CHONPS (Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur)

• Trace elements like iodine and fluoride are obtained from iodized salt, seafood, tap water, and toothpaste.

Classification of Elements

• Elements can be classified as metals, nonmetals, or metalloids.

Atomic Number and Mass

• Atomic number: Number of protons in an atom; defines the element.

• Atomic mass: Sum of protons and neutrons in the nucleus.

Electron Shells and Valence Electrons

Electrons occupy energy levels or "shells" around the nucleus. The outermost shell contains valence electrons, which determine an atom's reactivity.

• 1st shell: 2 electrons

• 2nd shell: 8 electrons

• 3rd shell: 18 electrons

• Octet Rule: Atoms are most stable when their outer shell has 8 electrons (except hydrogen and helium, which are stable with 2).

Ions and Isotopes

• Ion: Atom that has gained or lost electrons, resulting in a charge (gain = negative ion, lose = positive ion).

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

Radioactive Isotopes

Some isotopes are unstable and decay spontaneously, emitting radiation. These radioactive isotopes are used in medical procedures but can be dangerous in large quantities.

Chemical Bonds and Molecules

Chemical Formulas

A chemical formula shows the ratio of atoms in a molecule or compound (e.g., H2O means two hydrogens for every one oxygen).

Molecules vs. Compounds

• Molecule: Two or more atoms chemically bonded (can be the same element, e.g., O2).

• Compound: Molecule with atoms of two or more different elements (e.g., H2O, NaCl).

Types of Chemical Bonds

• Ionic Bonds: Electrons are transferred from one atom to another, forming positive and negative ions that attract each other. Usually between metals and nonmetals. Example: NaCl.

• Covalent Bonds: Electrons are shared between atoms. Usually between nonmetals. Can be polar (unequal sharing) or non-polar (equal sharing).

• Hydrogen Bonds: Weak attraction between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen). Important in water and biological molecules.

Water: Properties and Importance

Structure and Polarity of Water

Water (H2O) is a polar molecule, meaning it has slightly charged ends due to unequal sharing of electrons in its covalent bonds. This polarity allows water molecules to form hydrogen bonds with each other.

Unique Properties of Water

• Cohesion: Water molecules stick to each other, leading to surface tension.

• Adhesion: Water molecules stick to other substances, enabling capillary action (movement up plant stems).

• High Specific Heat: Water resists temperature changes, helping regulate climate and body temperature.

• High Heat of Vaporization: Requires a lot of energy to change from liquid to gas, important for cooling mechanisms like sweating.

• Density of Ice: Solid water (ice) is less dense than liquid water, so ice floats, insulating aquatic life in winter.

• Excellent Solvent: Water dissolves many ions and polar molecules, facilitating chemical reactions in cells.

Macromolecules: The Molecules of Life

Carbon Chemistry

Carbon is the backbone of organic molecules due to its ability to form four covalent bonds, resulting in diverse structures (chains, rings, branches).

The Four Major Biomolecules

• Carbohydrates: Sugars and starches; provide energy and structural support.

• Lipids: Fats, oils, and steroids; store energy, form membranes, and act as signaling molecules.

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

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

Monomers and Polymers

• Monomer: Small building block molecule (e.g., monosaccharide, amino acid, nucleotide, fatty acid).

• Polymer: Large molecule made of repeating monomers (e.g., polysaccharide, polypeptide, nucleic acid, triglyceride).

Building and Breaking Polymers

• Dehydration Synthesis: Joins monomers by removing water; requires energy.

• Hydrolysis: Breaks polymers into monomers by adding water; releases energy.

Carbohydrates

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

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

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

Lipids

• Monomer: Fatty acids and glycerol

• Polymers: Triglycerides, phospholipids, steroids

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

• Saturated fats: Solid at room temperature, all single bonds

• Unsaturated fats: Liquid at room temperature, contain double bonds

Proteins

• Monomer: Amino acid (20 types)

• Polymer: Polypeptide (protein)

• Functions: Catalysis (enzymes), structure, transport, signaling

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

Nucleic Acids

• Monomer: Nucleotide (phosphate, sugar, base)

• Polymers: 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. Some reactions release energy (exergonic), while others absorb energy (endergonic).

• Activation Energy: The energy required to start a reaction.

Enzymes

• Enzyme: A protein that acts as a catalyst, speeding up chemical reactions by lowering activation energy.

• Enzymes are specific to their substrates and are reusable.

• Factors such as temperature and pH can denature enzymes, altering their function.

Enzyme-Substrate Interaction

• Lock and Key Model: Substrate binds to the enzyme's active site, reaction occurs, and products are released.

Nutrition and Macromolecules in Food

Carbohydrates in Diet

• Monosaccharides (simple sugars): Quick energy, found in fruits and processed foods.

• Polysaccharides (complex carbs): Long-term energy, found in bread, pasta, potatoes.

• Cellulose (fiber): Indigestible by humans, important for digestive health.

Lipids in Diet

• Unsaturated fats: Healthier, found in fish, nuts, plant oils.

• Saturated fats and trans fats: Less healthy, found in meats, butter, processed foods.

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

• Cholesterol: LDL ("bad") can build up in blood vessels; HDL ("good") helps remove LDL.

Proteins in Diet

• Essential amino acids: Must be obtained from food; animal proteins are usually "complete" sources.

• Food allergies: Immune response to specific proteins.

Nucleic Acids in Diet

• Present in all living cells; broken down into nucleotides for use in the body.

Summary Table: Macromolecules