The Molecules of Cells

Introduction to Organic Compounds (3.1-3.3)
- Carbon-containing compounds are the chemical building blocks of life.
Carbohydrates (3.4-3.7)
- Carbohydrates serve as a cell's fuel and building material.
Lipids (3.8-3.11)
- Lipids are hydrophobic molecules with diverse functions.

Digestion of lactose depends on body chemistry. Individuals may digest milk well or experience discomfort/illness depending on lactose tolerance.
Lactose intolerance is common in adults due to the decline in the enzyme lactase after age 2.
Lactase enzyme breakdown: Lactose (sugar) is broken down by lactase (protein), which is controlled by a gene made of DNA (nucleic acid).
Molecular interactions drive biological processes, focusing on sugars, proteins, fats, and nucleic acids.

Processes of hydrolysis and dehydration are analogous to building and disassembling structures.
Starch and fiber comparison: glucose bonds in fiber are indigestible to humans, while starch bonds are digestible.
Dietary fats ranking: unsaturated > saturated > trans.

Carbon's Role: Carbon is essential for forming complex molecules that are the backbone of organic compounds, often combined with hydrogen.
Isomers: Compounds like C4H8 can have different structures (isomers) leading to different properties.
Importance of shape and structure in pharmaceuticals and biological effectiveness.
Hydrocarbons: Major components of petroleum, essential for energy.
Carbon skeleton diversity includes variations in length, branching, and ring structures.

Properties of organic compounds depend on carbon backbones and attached chemical groups.
Functional Groups:
1. Hydroxyl group (-OH): forms alcohols (e.g., ethanol).
2. Carbonyl group (C=O): present in sugars, affects structure and reactivity.
3. Carboxyl group (-COOH): acts as an acid, forms carboxylic acids.
4. Amino group (-NH2): basic, forms amines.
5. Phosphate group: essential for energy transfers (ATP).
6. Methyl group (-CH3): non-polar, affects molecular shape and gene expression.

Macromolecules: Key classes include carbohydrates, lipids, proteins, and nucleic acids, which are formed from simpler units (monomers).
Polymers: Comprised of repeated monomers joined by dehydration reactions, where water is removed. Example: linking glucose to form starch.
Hydrolysis: Process of breaking polymers into monomers by adding water, essential for digestion.
Enzymes: Required for both dehydration and hydrolysis reactions.
Molecular Diversity: Despite the complexity, a limited set of monomers (e.g., 20 amino acids) generates vast macromolecule diversity.

Definition: Simplest carbohydrates (e.g., glucose, fructose), generally depicted with the formula (CH2O)n.
Functions: Serve as energy fuels, with glucose as a primary energy source for cells.
Isomer examples: Glucose and fructose (C6H12O6) have different properties due to arrangement differences.

Formed from two monosaccharides: e.g., maltose from glucose units through dehydration.
Sucrose: Main disaccharide composed of glucose and fructose, vital for energy transport in plants.
Lactose: Made from glucose and galactose; relevant for understanding lactose intolerance.

Daily sugar intake statistics: Americans consume 22 teaspoons of sugar/day.
Health implications: WHO recommends ≤10% of calories from added sugars. Link between high sugar intake and health risks (e.g., obesity, heart disease).

Definition: Long chains of monosaccharide units; may function as storage (e.g., starch, glycogen) or structural compounds (e.g., cellulose).
Starch: Plant storage polysaccharide, digestible, hydrolyzed to release glucose.
Glycogen: Animal storage polysaccharide, highly branched, stored mainly in liver and muscles.
Cellulose: Major component of plant cell walls, undigestible for humans, contributes to dietary fiber.

Definition: Lipids mainly intended for energy storage.
Types: Fats (triglycerides) composed of glycerol and fatty acids (saturated vs. unsaturated).
Saturated fatty acids: No double bonds, solid at room temperature; common in animal fats.
Unsaturated fatty acids: One or more double bonds, liquid at room temperature (e.g., oils from plants).

Trans fats produced through hydrogenation of unsaturated fats raise health concerns, contributing to heart disease risk.
Regulatory measures include labeling trans fat content and bans in various jurisdictions.

Phospholipids form cell membrane structures with hydrophilic heads and hydrophobic tails.
Steroids: Four fused rings structure, encompassing cholesterol, vital for membrane integrity, and other hormonal functions.

Composition: Polymers of amino acids connected via peptide bonds, crucial for functions across biological systems.
Functions: Enzymes, transport, defensive (antibodies), and structural components of bodies.

Structure: Comprised of an amino group, carboxyl group, and an R group; 20 amino acids exist, determining protein diversity.
Formation of polypeptides through dehydration, resulting in dipeptides and larger chains.

Types: DNA and RNA, essential for genetic information storage and transfer.
Structure: Nucleotides consist of a sugar, phosphate group, and nitrogenous base.
Functional roles: DNA directs the synthesis of proteins through template-strand mechanisms.

Evolutionary insight: Lactase persistence in certain populations provides selective advantage in dairy farming cultures. Genetic mutations leading to lactose tolerance highlight human adaptation through dietary shifts.

Carbohydrates, lipids, proteins, and nucleic acids exemplify biological macromolecules; their unique properties arise from structural organization and chemical functionalities, directly tied to life processes. Understanding these molecules illuminates biochemical interactions crucial for cellular function and organismal health.

Consider the implications of sugar consumption on health and metabolism and reflect on the importance of healthy dietary choices.