Chapter 2: The Chemical Basis of Life – Study Notes

Chapter 2: The Chemical Basis of Life

Course Learning Objectives

This chapter introduces the chemical principles underlying biological molecules and their roles in the human body. Students will learn to distinguish between organic and inorganic molecules, understand the structure and function of major biomolecules, and interpret the pH scale and buffer systems.

• Describe the chemical basis of common organic and inorganic molecules in the human body.

• Differentiate between proteins, carbohydrates, lipids, and nucleic acids.

• Define organic and inorganic molecules.

• Explain how organic molecule building blocks form the human body.

• Interpret the pH scale and recall the pH of common fluids.

• Define acid, base, salt, pH, buffer, alkalosis, and acidosis.

• Describe buffer systems and their role in acid/base balance.

Energy in Biological Systems

Forms of Energy

Energy is the capacity to do work and is essential for all biological processes. It exists in various forms, including kinetic, potential, and chemical energy.

• Kinetic Energy: The energy of motion. For example, a moving cyclist has kinetic energy.

• Potential Energy: Stored energy due to position or structure. A cyclist at the top of a hill has potential energy.

• Chemical Energy: Energy stored in chemical bonds, such as those in food molecules.

Example: Glucose contains chemical energy that cells convert to ATP for cellular work.

Glucose and Glycogen

• Glucose: A simple sugar (monosaccharide) found in food; primary source for ATP production.

• Glycogen: A polysaccharide; storage form of glucose in the liver, skeletal muscle, and fat.

Adenosine Triphosphate (ATP)

ATP is the main energy currency of the cell, storing and releasing energy as needed for cellular processes.

• Full Name: Adenosine triphosphate

• Function: Stores energy in high-energy phosphate bonds.

• Energy Release: When ATP is hydrolyzed to ADP and inorganic phosphate ($ATP \rightarrow ADP + P_i$), energy is released for cellular work.

Structure of ATP: Consists of adenine (a nitrogenous base), ribose (a five-carbon sugar), and three phosphate groups.

Inorganic Chemistry

Definition and Examples

Inorganic chemistry deals with substances that generally do not contain both carbon and hydrogen atoms together.

• Examples: Oxygen ($O_2$), carbon dioxide ($CO_2$), and water ($H_2O$).

Note: Some exceptions exist, such as carbonates and cyanides, but the general rule applies in biological contexts.

Organic Chemistry

Major Classes of Biological Molecules

Organic molecules contain carbon and are the foundation of life. There are four major classes:

• Carbohydrates

• Proteins

• Lipids

• Nucleic acids

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically in a 2:1 ratio of hydrogen to oxygen.

• Monosaccharides: Simple sugars (e.g., glucose, fructose); building blocks of carbohydrates.

• Disaccharides: Two monosaccharides joined together (e.g., sucrose = glucose + fructose; lactose = glucose + galactose).

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

Functions:

• Short-term energy storage

• Converted quickly to glucose for ATP production

• Essential for cellular metabolism

Proteins

Proteins are complex molecules made of amino acids and are vital for structure and function in the body.

• Elements: Carbon, hydrogen, oxygen, nitrogen

• Building Blocks: Amino acids (each contains an amine group and a carboxyl group)

• Note: Amino acids are not stored in the body; a daily supply is required from the diet.

Functions:

• Structural components (skin, hair, nails, muscles)

• Transport (hemoglobin)

• Enzymes (catalyze biochemical reactions)

• Immune defense (antibodies)

• Muscle contraction (actin and myosin)

Lipids

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

• Elements: Carbon, hydrogen, oxygen (less oxygen than carbohydrates)

• Building Blocks: Glycerol and fatty acids

• Types: Fats, oils, cholesterol, triglycerides, phospholipids

Functions:

• Long-term energy storage

• Insulation against heat loss

• Protection of organs

• Component of cell membranes (cholesterol, phospholipids)

Types of Lipids

• Saturated: Only single covalent bonds between carbon atoms (e.g., animal fats like beef, pork, whole milk, cheese, eggs)

• Unsaturated: One or more double covalent bonds between carbon atoms (e.g., olive oil, fish oil, sunflower oil)

• Triglycerides: Most common lipid; composed of glycerol and three fatty acids

• Eicosanoids: Regulatory molecules derived from fatty acids (e.g., prostaglandins regulate hormones and blood clotting)

• Steroids: Four-ring structure; cholesterol is a key steroid, precursor to bile salts, estrogen, progesterone, testosterone

Nucleic Acids

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

• Elements: Carbon, hydrogen, oxygen, nitrogen, phosphorus

• Building Blocks: Nucleotides (each consists of a nitrogenous base, a phosphate group, and a five-carbon sugar—ribose or deoxyribose)

• Types: DNA (deoxyribonucleic acid), RNA (ribonucleic acid)

Acids, Bases, and the pH Scale

Definitions

• Acid: Substance that donates a hydrogen ion (H+); pH below 7 (e.g., hydrochloric acid, HCl)

• Base: Substance that accepts a hydrogen ion (H+); pH above 7 (e.g., sodium hydroxide, NaOH)

• Neutral: pH of 7 (e.g., pure water)

The pH Scale

The pH scale measures the concentration of hydrogen ions in a solution. It ranges from 0 (most acidic) to 14 (most basic).

• Each unit change represents a tenfold change in H+ concentration.

• pH is calculated as: $pH = -\log_{10}[H^+]$

Acid-Base Balance and Buffers

• Buffer: A substance that minimizes changes in pH by absorbing or releasing H+ ions.

• Physiological Buffers: Main buffer systems in the human body include the bicarbonate buffer system, phosphate buffer system, and protein buffer system.

• Acidosis: Condition where blood pH falls below normal (can be respiratory or metabolic in origin).

• Alkalosis: Condition where blood pH rises above normal (can be respiratory or metabolic in origin).

Example: The bicarbonate buffer system helps maintain blood pH by converting excess H+ to carbonic acid, which can then be converted to carbon dioxide and exhaled.

Summary Table: Major Classes of Biological Molecules

Class	Elements	Building Blocks	Main Functions	Examples
Carbohydrates	C, H, O	Monosaccharides	Short-term energy, structure	Glucose, starch, glycogen
Proteins	C, H, O, N	Amino acids	Structure, enzymes, transport, defense	Hemoglobin, enzymes, antibodies
Lipids	C, H, O	Glycerol, fatty acids	Long-term energy, insulation, membranes	Triglycerides, cholesterol, phospholipids
Nucleic Acids	C, H, O, N, P	Nucleotides	Genetic information, protein synthesis	DNA, RNA

Additional info: For further study, review textbook Chapter 2 (pages 30-39) and complete related Smartbook activities and quizzes.