Atoms and Elements

Definition and Structure of an Atom

An atom is the smallest unit of matter that retains the properties of an element. Atoms are composed of three subatomic particles: protons (positively charged), neutrons (neutral), and electrons (negatively charged). Protons and neutrons are located in the nucleus, while electrons orbit the nucleus in electron shells.

• Subatomic particles: Protons (+), Neutrons (0), Electrons (–)

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

• Mass number: Sum of protons and neutrons.

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

Example: Carbon-12 and Carbon-14 are isotopes of carbon.

Elements in the Human Body

Elements are pure substances consisting of only one type of atom. The most common elements in the human body are oxygen, carbon, hydrogen, and nitrogen. These elements are essential for forming biomolecules and supporting life processes.

• Major elements: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N)

• Trace elements: Iron (Fe), Iodine (I), Zinc (Zn), etc.

Chemical Bonds and Compounds

Types of Chemical Bonds

Chemical bonds are forces that hold atoms together in compounds. The main types are ionic, covalent, and hydrogen bonds.

• Ionic bonds: Formed when electrons are transferred from one atom to another, creating ions (charged atoms).

• Covalent bonds: Formed when atoms share electrons. Can be non-polar (equal sharing) or polar (unequal sharing).

• Hydrogen bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

Example: Water molecules are held together by hydrogen bonds.

Reactivity and Electron Configuration

The reactivity of an atom depends on its electron configuration, especially the electrons in the outermost shell (valence electrons). Atoms tend to react to achieve a full valence shell, often resulting in the formation of chemical bonds.

Water and Its Importance

Properties and Functions of Water

Water is vital for life due to its unique properties, such as high heat capacity, solvent abilities, and participation in chemical reactions. It serves as a medium for biochemical reactions, helps regulate temperature, and transports substances in the body.

• Hydrophilic: Substances that dissolve in water (water-loving).

• Hydrophobic: Substances that do not dissolve in water (water-fearing).

Example: Cell membranes are composed of hydrophobic lipid bilayers.

Chemical Reactions and Enzymes

Types of Chemical Reactions

Chemical reactions involve the making or breaking of chemical bonds. In the body, common types include synthesis, decomposition, and exchange reactions.

• Synthesis reaction: Two or more substances combine to form a more complex product.

• Decomposition reaction: A complex molecule breaks down into simpler substances.

• Exchange reaction: Parts of molecules are exchanged.

Enzymes and Activation Energy

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required. They are specific to substrates and are not consumed in the reaction.

• Activation energy: The minimum energy required to start a chemical reaction.

• Catalyst: A substance that increases the rate of a reaction without being used up.

Example: Digestive enzymes break down food molecules in the gut.

Acids, Bases, and pH

Definition and Importance of pH

The pH scale measures the concentration of hydrogen ions (H+) in a solution. It ranges from 0 (very acidic) to 14 (very basic), with 7 being neutral.

• Acid: Substance that releases H+ ions in solution (pH < 7).

• Base: Substance that accepts H+ ions or releases OH– ions (pH > 7).

• Buffer: A system that resists changes in pH by neutralizing added acids or bases.

Example: Blood contains buffers to maintain a stable pH around 7.4.

Biological Macromolecules

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as a primary energy source for cells.

• Structure: Monosaccharides (simple sugars), disaccharides, polysaccharides.

• Examples: Glucose, starch, glycogen.

• Function: Energy storage and supply.

• Synthesis: Formed by dehydration synthesis; broken down by hydrolysis.

Lipids

Lipids are hydrophobic molecules including fats, oils, and steroids. They are important for energy storage, insulation, and cell membrane structure.

• Structure: Glycerol backbone with fatty acid chains.

• Examples: Triglycerides, phospholipids, cholesterol.

• Function: Long-term energy storage, membrane structure, signaling.

• Saturated vs. Unsaturated Fats: Saturated fats have no double bonds; unsaturated fats have one or more double bonds.

Proteins

Proteins are polymers of amino acids and perform a wide range of functions in the body, including catalysis, structure, and transport.

• Structure: Four levels – primary, secondary, tertiary, quaternary.

• Examples: Enzymes, antibodies, hemoglobin.

• Function: Catalysis, support, transport, defense.

• Denaturation: Loss of protein structure and function due to environmental changes.

Nucleic Acids

Nucleic acids store and transmit genetic information. The two main types are DNA and RNA.

• Structure: Chains of nucleotides (sugar, phosphate, nitrogenous base).

• DNA: Double helix, stores genetic code, base pairs: A-T, C-G.

• RNA: Single-stranded, involved in protein synthesis, base pairs: A-U, C-G.

High-Energy Compounds

ATP and Cellular Energy

High-energy compounds, such as adenosine triphosphate (ATP), store and provide energy for cellular processes. ATP releases energy when its phosphate bonds are broken.

• Function: Powers cellular work (muscle contraction, active transport, biosynthesis).

• Example: ATP is the primary energy currency of the cell.