Molecules of Life

Introduction

All living organisms are composed of four major classes of biological macromolecules: carbohydrates, lipids, proteins, and nucleic acids. These molecules are essential for structure, function, and regulation of the body's tissues and organs.

Cellular Energy: ATP

Adenosine Triphosphate (ATP)

ATP is the primary energy carrier in cells. It consists of adenosine (a nitrogenous base attached to a ribose sugar) and three phosphate groups. Energy is released when ATP reacts with water (hydrolysis), forming ADP (adenosine diphosphate) and inorganic phosphate.

• ATP Structure: Adenosine + 3 phosphate groups

• Hydrolysis Reaction:

• Function: Provides energy for cellular processes

Polymers and Monomers

Definition and Diversity

Macromolecules are large molecules made up of smaller units called monomers. Polymers are chains of monomers linked by covalent bonds. The diversity of macromolecules arises from the variety and sequence of monomers.

• Polymer: A large molecule composed of repeating monomer units

• Monomer: A small molecule that can join with others to form a polymer

• Cellular Diversity: Each cell type has a unique set of macromolecules based on its function

• Variation: Polymers differ by monomer type, sequence, functional groups, and resulting polarity/charge

Properties of Water-Soluble Molecules

Bond Types and Solubility

Molecules that are soluble in water typically have polar covalent bonds. These bonds create regions of partial positive and negative charges, allowing interaction with water molecules.

• Polar Covalent Bond: Electrons are shared unequally, creating polarity

• Hydrogen Bonds: Form between polar molecules and water

• Hydrophobic Interaction: Nonpolar molecules do not dissolve in water

Macromolecule Synthesis

Dehydration Synthesis

Macromolecules are formed by dehydration synthesis, where monomers are joined and water is released. Observing synthesis, more of the product macromolecule appears.

• Dehydration Reaction:

• Example: Formation of proteins from amino acids

Carbohydrates

Structure and Types

Carbohydrates are organic molecules with carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio. They are classified as monosaccharides, disaccharides, and polysaccharides.

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

• Disaccharides: Two monosaccharides joined by a glycosidic bond (e.g., sucrose, lactose)

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

Monosaccharides

Monosaccharides are the building blocks of carbohydrates. They can exist in linear or ring forms and may be classified as aldoses or ketoses based on the position of the carbonyl group.

• Glucose: An aldose sugar, important for energy

• Ribose: A component of RNA

• Isomers: Molecules with the same formula but different structures

Disaccharides

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

• Sucrose: Glucose + Fructose

• Lactose: Glucose + Galactose

Polysaccharides

Polysaccharides serve as energy storage or structural components.

• Starch: Energy storage in plants

• Glycogen: Energy storage in animals

• Cellulose: Structural component in plant cell walls

• Chitin: Structural component in fungal cell walls and arthropod exoskeletons

Lipids

Structure and Types

Lipids are hydrophobic molecules, including fats, oils, waxes, and steroids. They are not true polymers and are composed mainly of hydrocarbons.

• Fats (Triglycerides): Glycerol + 3 fatty acids, joined by ester linkages

• Phospholipids: Glycerol + 2 fatty acids + phosphate group; major component of cell membranes

• Steroids: Four fused carbon rings (e.g., cholesterol, hormones)

Saturated vs. Unsaturated Fatty Acids

Fatty acids can be saturated (no double bonds) or unsaturated (one or more double bonds).

• Saturated: Straight chains, solid at room temperature, found in animal fats

• Unsaturated: Bent chains due to double bonds, liquid at room temperature, found in plant oils

• Trans Fats: Artificially hydrogenated unsaturated fats, associated with poor cardiovascular health

Phospholipids and Membranes

Phospholipids have both hydrophilic (phosphate head) and hydrophobic (fatty acid tails) regions, allowing them to form bilayers in water, which are the basis of cell membranes.

• Bilayer Formation: Hydrophilic heads face water, hydrophobic tails face inward

• Function: Structural component of cell membranes

Proteins

Structure and Function

Proteins are polymers of amino acids and perform a vast array of functions in cells, including catalysis, structure, transport, and signaling.

• Amino Acids: 20 different types, each with a unique side chain (R group)

• Peptide Bonds: Covalent bonds joining amino acids

• Functions: Enzymes, structural support, movement, transport, signaling

Levels of Protein Structure

• Primary Structure: Sequence of amino acids

• Secondary Structure: Local folding (alpha helix, beta sheet) stabilized by hydrogen bonds

• Tertiary Structure: Overall 3D shape due to interactions among side chains (hydrophobic interactions, disulfide bridges)

• Quaternary Structure: Association of multiple polypeptide chains

Protein Denaturation

Extreme conditions (high temperature, acidic or basic pH) can cause proteins to lose their shape and function, a process called denaturation.

Nucleic Acids

Structure and Function

Nucleic acids (DNA and RNA) store and transmit genetic information. They are polymers of nucleotides, each consisting of a phosphate group, a pentose sugar, and a nitrogenous base.

• DNA: Deoxyribonucleic acid, double-stranded, contains adenine (A), thymine (T), cytosine (C), guanine (G)

• RNA: Ribonucleic acid, single-stranded, contains adenine (A), uracil (U), cytosine (C), guanine (G)

• Nucleotide Structure: Phosphate + Sugar (ribose or deoxyribose) + Nitrogenous base

Base Pairing

• Adenine (A) pairs with Thymine (T) in DNA (2 hydrogen bonds)

• Cytosine (C) pairs with Guanine (G) (3 hydrogen bonds)

• RNA: Uracil (U) replaces Thymine (T)

Function

• DNA: Stores hereditary information

• RNA: Transfers genetic code from DNA to ribosomes for protein synthesis

Additional info: Some explanations and tables were expanded for clarity and completeness based on standard biology curriculum.