Elements

Definition and Biological Importance

Elements are fundamental substances that cannot be broken down into simpler substances by chemical means. They are the building blocks for all matter, including biological molecules essential for life.

• Element: A pure substance consisting of only one type of atom.

• Major biological elements: Oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).

• These elements form molecules such as carbohydrates, proteins, lipids, and nucleic acids, which are vital for cell structure and function.

• Trace elements: Elements required in very small quantities (e.g., iron (Fe), iodine (I), copper (Cu)).

• Other elements may be present in smaller quantities.

Subatomic Particles

Structure of Atoms

Atoms are the smallest units of matter and the building blocks of the physical world. They consist of subatomic particles that determine their properties and behavior.

• Protons: Positively charged particles (+)

• Neutrons: Uncharged particles

• Electrons: Negatively charged particles (-)

• Atoms of the same element may have different numbers of neutrons; these are called isotopes.

Compounds

Formation and Types of Chemical Bonds

Compounds are substances formed from two or more elements joined by chemical bonds. The properties of compounds depend on the types of atoms and bonds involved.

• Ionic bonds: Formed when electrons are transferred from one atom to another, resulting in charged ions held together by electrostatic forces.

• Covalent bonds: Formed when atoms share electrons. If electrons are shared equally, the bond is non-polar; if unequally, the bond is polar.

• Hydrogen bonds: Weak chemical bonds that form when a hydrogen atom covalently bonded to one atom is attracted to another electronegative atom.

Water: The Versatile Molecule

Properties and Biological Significance

Water is essential for life due to its unique chemical and physical properties, which arise from its molecular structure and hydrogen bonding.

• Cohesion: Water molecules stick together due to hydrogen bonding.

• Adhesion: Water molecules stick to other surfaces.

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

• Capillary action: The combination of cohesion and adhesion allows water to move up narrow tubes, such as plant roots and stems.

• Water has a high specific heat, high heat of vaporization, and expands upon freezing.

Acids and Bases

pH and Chemical Reactions

Acids and bases are substances that affect the hydrogen ion concentration in solutions, influencing chemical reactions and biological processes.

• Acid: A substance that increases the hydrogen ion () concentration in a solution.

• Base: A substance that decreases the hydrogen ion concentration, often by releasing hydroxide ions ().

• pH scale: Measures the acidity or basicity of a solution, ranging from 1 (most acidic) to 14 (most basic). Neutral pH is 7.

• pH formula:

• The pH scale is logarithmic; each unit represents a tenfold change in concentration.

Organic Molecules

Types and Functions

Organic molecules contain carbon and are essential for life. They include carbohydrates, proteins, lipids, and nucleic acids.

• Organic compounds: Molecules with carbon; those without carbon are inorganic.

• Carbon is versatile, forming four covalent bonds with other atoms, including hydrogen, oxygen, and nitrogen.

• Macromolecules: Large polymers made from smaller monomers.

• Polymerization: Monomers are joined by dehydration synthesis (condensation) reactions, releasing water.

• Hydrolysis: Polymers are broken down into monomers by adding water.

• Four major classes of organic compounds: carbohydrates, lipids, proteins, nucleic acids.

Carbohydrates

Classification and Functions

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as energy sources and structural components.

• Classified as monosaccharides, disaccharides, or polysaccharides based on the number of sugar units.

• The term "saccharide" means sugar; prefixes indicate the number of units.

Monosaccharides

Monosaccharides are the simplest carbohydrates and serve as energy sources.

• Glucose and fructose are common monosaccharides. Their chemical formula is .

• Glucose is vital for cellular respiration and photosynthesis.

• Monosaccharides can exist as straight chains or rings.

Disaccharides

Disaccharides are formed by joining two monosaccharides via a glycosidic linkage.

• Maltose: Formed from two glucose molecules.

• Sucrose: Formed from glucose and fructose.

• Disaccharides are broken down into monosaccharides by hydrolysis.

Polysaccharides

Polysaccharides are large carbohydrates made of many monosaccharide units.

• Starch: Storage polysaccharide in plants.

• Glycogen: Storage polysaccharide in animals.

• Cellulose: Structural polysaccharide in plant cell walls.

• Polysaccharides can be branched or unbranched.

Proteins

Structure and Function

Proteins are polymers made of amino acids and are essential for structure, function, and regulation of tissues and organs.

• Proteins contain carbon, hydrogen, oxygen, and nitrogen.

• There are 20 different amino acids, each with a central carbon atom, an amino group (), a carboxyl group (), a hydrogen atom, and an R group (side chain).

• Amino acids differ only in the R group, which determines their properties.

• Amino acids are joined by peptide bonds to form polypeptides.

• Proteins are classified based on the properties of their R groups: hydrophobic (non-polar), hydrophilic (polar), and charged.

Lipids

Types and Functions

Lipids are hydrophobic molecules important for energy storage, insulation, and cell membrane structure.

• Fats: Made of glycerol and fatty acids. Fatty acids can be saturated or unsaturated.

• Phospholipids: Major component of cell membranes; consist of a hydrophilic head and hydrophobic tails.

• Cholesterol: Steroid molecule important for membrane structure and as a precursor for hormones.

Nucleic Acids

Structure and Function

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

• Composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus.

• Monomers are nucleotides, each consisting of a sugar, phosphate group, and nitrogenous base.

• DNA stores genetic information; RNA is involved in protein synthesis.

Summary Table: Major Classes of Organic Compounds